// SPDX-License-Identifier: GPL-2.0-or-later
/*
 */

#include <linux/init.h>
#include <linux/slab.h>
#include <linux/bitrev.h>
#include <linux/ratelimit.h>
#include <linux/usb.h>
#include <linux/usb/audio.h>
#include <linux/usb/audio-v2.h>

#include <sound/core.h>
#include <sound/pcm.h>
#include <sound/pcm_params.h>

#include "usbaudio.h"
#include "card.h"
#include "quirks.h"
#include "endpoint.h"
#include "helper.h"
#include "pcm.h"
#include "clock.h"
#include "power.h"
#include "media.h"
#include "implicit.h"

#define SUBSTREAM_FLAG_DATA_EP_STARTED  0
#define SUBSTREAM_FLAG_SYNC_EP_STARTED  1

/* return the estimated delay based on USB frame counters */
static snd_pcm_uframes_t snd_usb_pcm_delay(struct snd_usb_substream *subs,
                                           struct snd_pcm_runtime *runtime)
{
        unsigned int current_frame_number;
        unsigned int frame_diff;
        int est_delay;
        int queued;

        if (subs->direction == SNDRV_PCM_STREAM_PLAYBACK) {
                queued = bytes_to_frames(runtime, subs->inflight_bytes);
                if (!queued)
                        return 0;
        } else if (!subs->running) {
                return 0;
        }

        current_frame_number = usb_get_current_frame_number(subs->dev);
        /*
         * HCD implementations use different widths, use lower 8 bits.
         * The delay will be managed up to 256ms, which is more than
         * enough
         */
        frame_diff = (current_frame_number - subs->last_frame_number) & 0xff;

        /* Approximation based on number of samples per USB frame (ms),
           some truncation for 44.1 but the estimate is good enough */
        est_delay = frame_diff * runtime->rate / 1000;

        if (subs->direction == SNDRV_PCM_STREAM_PLAYBACK) {
                est_delay = queued - est_delay;
                if (est_delay < 0)
                        est_delay = 0;
        }

        return est_delay;
}

/*
 * return the current pcm pointer.  just based on the hwptr_done value.
 */
static snd_pcm_uframes_t snd_usb_pcm_pointer(struct snd_pcm_substream *substream)
{
        struct snd_pcm_runtime *runtime = substream->runtime;
        struct snd_usb_substream *subs = runtime->private_data;
        unsigned int hwptr_done;

        if (atomic_read(&subs->stream->chip->shutdown))
                return SNDRV_PCM_POS_XRUN;
        scoped_guard(spinlock, &subs->lock) {
                hwptr_done = subs->hwptr_done;
                runtime->delay = snd_usb_pcm_delay(subs, runtime);
        }
        return bytes_to_frames(runtime, hwptr_done);
}

/*
 * find a matching audio format
 */
static const struct audioformat *
find_format(struct list_head *fmt_list_head, snd_pcm_format_t format,
            unsigned int rate, unsigned int channels, bool strict_match,
            struct snd_usb_substream *subs)
{
        const struct audioformat *fp;
        const struct audioformat *found = NULL;
        int cur_attr = 0, attr;

        list_for_each_entry(fp, fmt_list_head, list) {
                if (strict_match) {
                        if (!(fp->formats & pcm_format_to_bits(format)))
                                continue;
                        if (fp->channels != channels)
                                continue;
                }
                if (rate < fp->rate_min || rate > fp->rate_max)
                        continue;
                if (!(fp->rates & SNDRV_PCM_RATE_CONTINUOUS)) {
                        unsigned int i;
                        for (i = 0; i < fp->nr_rates; i++)
                                if (fp->rate_table[i] == rate)
                                        break;
                        if (i >= fp->nr_rates)
                                continue;
                }
                attr = fp->ep_attr & USB_ENDPOINT_SYNCTYPE;
                if (!found) {
                        found = fp;
                        cur_attr = attr;
                        continue;
                }
                /* avoid async out and adaptive in if the other method
                 * supports the same format.
                 * this is a workaround for the case like
                 * M-audio audiophile USB.
                 */
                if (subs && attr != cur_attr) {
                        if ((attr == USB_ENDPOINT_SYNC_ASYNC &&
                             subs->direction == SNDRV_PCM_STREAM_PLAYBACK) ||
                            (attr == USB_ENDPOINT_SYNC_ADAPTIVE &&
                             subs->direction == SNDRV_PCM_STREAM_CAPTURE))
                                continue;
                        if ((cur_attr == USB_ENDPOINT_SYNC_ASYNC &&
                             subs->direction == SNDRV_PCM_STREAM_PLAYBACK) ||
                            (cur_attr == USB_ENDPOINT_SYNC_ADAPTIVE &&
                             subs->direction == SNDRV_PCM_STREAM_CAPTURE)) {
                                found = fp;
                                cur_attr = attr;
                                continue;
                        }
                }
                /* find the format with the largest max. packet size */
                if (fp->maxpacksize > found->maxpacksize) {
                        found = fp;
                        cur_attr = attr;
                }
        }
        return found;
}

const struct audioformat *
snd_usb_find_format(struct list_head *fmt_list_head, snd_pcm_format_t format,
                    unsigned int rate, unsigned int channels, bool strict_match,
                    struct snd_usb_substream *subs)
{
        return find_format(fmt_list_head, format, rate, channels, strict_match,
                        subs);
}
EXPORT_SYMBOL_GPL(snd_usb_find_format);

static const struct audioformat *
find_substream_format(struct snd_usb_substream *subs,
                      const struct snd_pcm_hw_params *params)
{
        return find_format(&subs->fmt_list, params_format(params),
                           params_rate(params), params_channels(params),
                           true, subs);
}

const struct audioformat *
snd_usb_find_substream_format(struct snd_usb_substream *subs,
                              const struct snd_pcm_hw_params *params)
{
        return find_substream_format(subs, params);
}
EXPORT_SYMBOL_GPL(snd_usb_find_substream_format);

bool snd_usb_pcm_has_fixed_rate(struct snd_usb_substream *subs)
{
        const struct audioformat *fp;
        struct snd_usb_audio *chip;
        int rate = -1;

        if (!subs)
                return false;
        chip = subs->stream->chip;
        if (!(chip->quirk_flags & QUIRK_FLAG_FIXED_RATE))
                return false;
        list_for_each_entry(fp, &subs->fmt_list, list) {
                if (fp->rates & SNDRV_PCM_RATE_CONTINUOUS)
                        return false;
                if (fp->nr_rates < 1)
                        continue;
                if (fp->nr_rates > 1)
                        return false;
                if (rate < 0) {
                        rate = fp->rate_table[0];
                        continue;
                }
                if (rate != fp->rate_table[0])
                        return false;
        }
        return true;
}

static int init_pitch_v1(struct snd_usb_audio *chip, int ep)
{
        struct usb_device *dev = chip->dev;
        unsigned char data[1];
        int err;

        data[0] = 1;
        err = snd_usb_ctl_msg(dev, usb_sndctrlpipe(dev, 0), UAC_SET_CUR,
                              USB_TYPE_CLASS|USB_RECIP_ENDPOINT|USB_DIR_OUT,
                              UAC_EP_CS_ATTR_PITCH_CONTROL << 8, ep,
                              data, sizeof(data));
        return err;
}

static int init_pitch_v2(struct snd_usb_audio *chip, int ep)
{
        struct usb_device *dev = chip->dev;
        unsigned char data[1];
        int err;

        data[0] = 1;
        err = snd_usb_ctl_msg(dev, usb_sndctrlpipe(dev, 0), UAC2_CS_CUR,
                              USB_TYPE_CLASS | USB_RECIP_ENDPOINT | USB_DIR_OUT,
                              UAC2_EP_CS_PITCH << 8, 0,
                              data, sizeof(data));
        return err;
}

/*
 * initialize the pitch control and sample rate
 */
int snd_usb_init_pitch(struct snd_usb_audio *chip,
                       const struct audioformat *fmt)
{
        int err;

        /* if endpoint doesn't have pitch control, bail out */
        if (!(fmt->attributes & UAC_EP_CS_ATTR_PITCH_CONTROL))
                return 0;

        usb_audio_dbg(chip, "enable PITCH for EP 0x%x\n", fmt->endpoint);

        switch (fmt->protocol) {
        case UAC_VERSION_1:
                err = init_pitch_v1(chip, fmt->endpoint);
                break;
        case UAC_VERSION_2:
                err = init_pitch_v2(chip, fmt->endpoint);
                break;
        default:
                return 0;
        }

        if (err < 0) {
                usb_audio_err(chip, "failed to enable PITCH for EP 0x%x\n",
                              fmt->endpoint);
                return err;
        }

        return 0;
}

static bool stop_endpoints(struct snd_usb_substream *subs, bool keep_pending)
{
        bool stopped = 0;

        if (test_and_clear_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags)) {
                snd_usb_endpoint_stop(subs->sync_endpoint, keep_pending);
                stopped = true;
        }
        if (test_and_clear_bit(SUBSTREAM_FLAG_DATA_EP_STARTED, &subs->flags)) {
                snd_usb_endpoint_stop(subs->data_endpoint, keep_pending);
                stopped = true;
        }
        return stopped;
}

static int start_endpoints(struct snd_usb_substream *subs)
{
        int err;

        if (!subs->data_endpoint)
                return -EINVAL;

        if (!test_and_set_bit(SUBSTREAM_FLAG_DATA_EP_STARTED, &subs->flags)) {
                err = snd_usb_endpoint_start(subs->data_endpoint);
                if (err < 0) {
                        clear_bit(SUBSTREAM_FLAG_DATA_EP_STARTED, &subs->flags);
                        goto error;
                }
        }

        if (subs->sync_endpoint &&
            !test_and_set_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags)) {
                err = snd_usb_endpoint_start(subs->sync_endpoint);
                if (err < 0) {
                        clear_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags);
                        goto error;
                }
        }

        return 0;

 error:
        stop_endpoints(subs, false);
        return err;
}

static void sync_pending_stops(struct snd_usb_substream *subs)
{
        snd_usb_endpoint_sync_pending_stop(subs->sync_endpoint);
        snd_usb_endpoint_sync_pending_stop(subs->data_endpoint);
}

/* PCM sync_stop callback */
static int snd_usb_pcm_sync_stop(struct snd_pcm_substream *substream)
{
        struct snd_usb_substream *subs = substream->runtime->private_data;

        sync_pending_stops(subs);
        return 0;
}

/* Set up sync endpoint */
int snd_usb_audioformat_set_sync_ep(struct snd_usb_audio *chip,
                                    struct audioformat *fmt)
{
        struct usb_device *dev = chip->dev;
        struct usb_host_interface *alts;
        struct usb_interface_descriptor *altsd;
        unsigned int ep, attr, sync_attr;
        bool is_playback;
        int err;

        if (fmt->sync_ep)
                return 0; /* already set up */

        alts = snd_usb_get_host_interface(chip, fmt->iface, fmt->altsetting);
        if (!alts)
                return 0;
        altsd = get_iface_desc(alts);

        err = snd_usb_parse_implicit_fb_quirk(chip, fmt, alts);
        if (err > 0)
                return 0; /* matched */

        /*
         * Generic sync EP handling
         */

        if (fmt->ep_idx > 0 || altsd->bNumEndpoints < 2)
                return 0;

        is_playback = !(get_endpoint(alts, 0)->bEndpointAddress & USB_DIR_IN);
        attr = fmt->ep_attr & USB_ENDPOINT_SYNCTYPE;
        if ((is_playback && (attr == USB_ENDPOINT_SYNC_SYNC ||
                             attr == USB_ENDPOINT_SYNC_ADAPTIVE)) ||
            (!is_playback && attr != USB_ENDPOINT_SYNC_ADAPTIVE))
                return 0;

        sync_attr = get_endpoint(alts, 1)->bmAttributes;

        /*
         * In case of illegal SYNC_NONE for OUT endpoint, we keep going to see
         * if we don't find a sync endpoint, as on M-Audio Transit. In case of
         * error fall back to SYNC mode and don't create sync endpoint
         */

        /* check sync-pipe endpoint */
        /* ... and check descriptor size before accessing bSynchAddress
           because there is a version of the SB Audigy 2 NX firmware lacking
           the audio fields in the endpoint descriptors */
        if ((sync_attr & USB_ENDPOINT_XFERTYPE_MASK) != USB_ENDPOINT_XFER_ISOC ||
            (get_endpoint(alts, 1)->bLength >= USB_DT_ENDPOINT_AUDIO_SIZE &&
             get_endpoint(alts, 1)->bSynchAddress != 0)) {
                dev_err(&dev->dev,
                        "%d:%d : invalid sync pipe. bmAttributes %02x, bLength %d, bSynchAddress %02x\n",
                           fmt->iface, fmt->altsetting,
                           get_endpoint(alts, 1)->bmAttributes,
                           get_endpoint(alts, 1)->bLength,
                           get_endpoint(alts, 1)->bSynchAddress);
                if (is_playback && attr == USB_ENDPOINT_SYNC_NONE)
                        return 0;
                return -EINVAL;
        }
        ep = get_endpoint(alts, 1)->bEndpointAddress;
        if (get_endpoint(alts, 0)->bLength >= USB_DT_ENDPOINT_AUDIO_SIZE &&
            get_endpoint(alts, 0)->bSynchAddress != 0 &&
            ((is_playback && ep != (unsigned int)(get_endpoint(alts, 0)->bSynchAddress | USB_DIR_IN)) ||
             (!is_playback && ep != (unsigned int)(get_endpoint(alts, 0)->bSynchAddress & ~USB_DIR_IN)))) {
                dev_err(&dev->dev,
                        "%d:%d : invalid sync pipe. is_playback %d, ep %02x, bSynchAddress %02x\n",
                           fmt->iface, fmt->altsetting,
                           is_playback, ep, get_endpoint(alts, 0)->bSynchAddress);
                if (is_playback && attr == USB_ENDPOINT_SYNC_NONE)
                        return 0;
                return -EINVAL;
        }

        fmt->sync_ep = ep;
        fmt->sync_iface = altsd->bInterfaceNumber;
        fmt->sync_altsetting = altsd->bAlternateSetting;
        fmt->sync_ep_idx = 1;
        if ((sync_attr & USB_ENDPOINT_USAGE_MASK) == USB_ENDPOINT_USAGE_IMPLICIT_FB)
                fmt->implicit_fb = 1;

        dev_dbg(&dev->dev, "%d:%d: found sync_ep=0x%x, iface=%d, alt=%d, implicit_fb=%d\n",
                fmt->iface, fmt->altsetting, fmt->sync_ep, fmt->sync_iface,
                fmt->sync_altsetting, fmt->implicit_fb);

        return 0;
}

static int snd_usb_pcm_change_state(struct snd_usb_substream *subs, int state)
{
        int ret;

        if (!subs->str_pd)
                return 0;

        ret = snd_usb_power_domain_set(subs->stream->chip, subs->str_pd, state);
        if (ret < 0) {
                dev_err(&subs->dev->dev,
                        "Cannot change Power Domain ID: %d to state: %d. Err: %d\n",
                        subs->str_pd->pd_id, state, ret);
                return ret;
        }

        return 0;
}

int snd_usb_pcm_suspend(struct snd_usb_stream *as)
{
        int ret;

        ret = snd_usb_pcm_change_state(&as->substream[0], UAC3_PD_STATE_D2);
        if (ret < 0)
                return ret;

        ret = snd_usb_pcm_change_state(&as->substream[1], UAC3_PD_STATE_D2);
        if (ret < 0)
                return ret;

        return 0;
}

int snd_usb_pcm_resume(struct snd_usb_stream *as)
{
        int ret;

        ret = snd_usb_pcm_change_state(&as->substream[0], UAC3_PD_STATE_D1);
        if (ret < 0)
                return ret;

        ret = snd_usb_pcm_change_state(&as->substream[1], UAC3_PD_STATE_D1);
        if (ret < 0)
                return ret;

        return 0;
}

static void close_endpoints(struct snd_usb_audio *chip,
                            struct snd_usb_substream *subs)
{
        if (subs->data_endpoint) {
                snd_usb_endpoint_set_sync(chip, subs->data_endpoint, NULL);
                snd_usb_endpoint_close(chip, subs->data_endpoint);
                subs->data_endpoint = NULL;
        }

        if (subs->sync_endpoint) {
                snd_usb_endpoint_close(chip, subs->sync_endpoint);
                subs->sync_endpoint = NULL;
        }
}

int snd_usb_hw_params(struct snd_usb_substream *subs,
                      struct snd_pcm_hw_params *hw_params)
{
        struct snd_usb_audio *chip = subs->stream->chip;
        const struct audioformat *fmt;
        const struct audioformat *sync_fmt;
        bool fixed_rate, sync_fixed_rate;
        int ret;

        ret = snd_media_start_pipeline(subs);
        if (ret)
                return ret;

        fixed_rate = snd_usb_pcm_has_fixed_rate(subs);
        fmt = find_substream_format(subs, hw_params);
        if (!fmt) {
                usb_audio_dbg(chip,
                              "cannot find format: format=%s, rate=%d, channels=%d\n",
                              snd_pcm_format_name(params_format(hw_params)),
                              params_rate(hw_params), params_channels(hw_params));
                ret = -EINVAL;
                goto stop_pipeline;
        }

        if (fmt->implicit_fb) {
                sync_fmt = snd_usb_find_implicit_fb_sync_format(chip, fmt,
                                                                hw_params,
                                                                !subs->direction,
                                                                &sync_fixed_rate);
                if (!sync_fmt) {
                        usb_audio_dbg(chip,
                                      "cannot find sync format: ep=0x%x, iface=%d:%d, format=%s, rate=%d, channels=%d\n",
                                      fmt->sync_ep, fmt->sync_iface,
                                      fmt->sync_altsetting,
                                      snd_pcm_format_name(params_format(hw_params)),
                                      params_rate(hw_params), params_channels(hw_params));
                        ret = -EINVAL;
                        goto stop_pipeline;
                }
        } else {
                sync_fmt = fmt;
                sync_fixed_rate = fixed_rate;
        }

        ret = snd_usb_lock_shutdown(chip);
        if (ret < 0)
                goto stop_pipeline;

        ret = snd_usb_pcm_change_state(subs, UAC3_PD_STATE_D0);
        if (ret < 0)
                goto unlock;

        if (subs->data_endpoint) {
                if (snd_usb_endpoint_compatible(chip, subs->data_endpoint,
                                                fmt, hw_params))
                        goto unlock;
                if (stop_endpoints(subs, false))
                        sync_pending_stops(subs);
                close_endpoints(chip, subs);
        }

        subs->data_endpoint = snd_usb_endpoint_open(chip, fmt, hw_params, false, fixed_rate);
        if (!subs->data_endpoint) {
                ret = -EINVAL;
                goto unlock;
        }

        if (fmt->sync_ep) {
                subs->sync_endpoint = snd_usb_endpoint_open(chip, sync_fmt,
                                                            hw_params,
                                                            fmt == sync_fmt,
                                                            sync_fixed_rate);
                if (!subs->sync_endpoint) {
                        ret = -EINVAL;
                        goto unlock;
                }

                snd_usb_endpoint_set_sync(chip, subs->data_endpoint,
                                          subs->sync_endpoint);
        }

        scoped_guard(mutex, &chip->mutex) {
                subs->cur_audiofmt = fmt;
        }

        if (!subs->data_endpoint->need_setup)
                goto unlock;

        if (subs->sync_endpoint) {
                ret = snd_usb_endpoint_set_params(chip, subs->sync_endpoint);
                if (ret < 0)
                        goto unlock;
        }

        ret = snd_usb_endpoint_set_params(chip, subs->data_endpoint);

 unlock:
        if (ret < 0)
                close_endpoints(chip, subs);

        snd_usb_unlock_shutdown(chip);
 stop_pipeline:
        if (ret < 0)
                snd_media_stop_pipeline(subs);

        return ret;
}
EXPORT_SYMBOL_GPL(snd_usb_hw_params);

/*
 * hw_params callback
 *
 * allocate a buffer and set the given audio format.
 *
 * so far we use a physically linear buffer although packetize transfer
 * doesn't need a continuous area.
 * if sg buffer is supported on the later version of alsa, we'll follow
 * that.
 */
static int snd_usb_pcm_hw_params(struct snd_pcm_substream *substream,
                                 struct snd_pcm_hw_params *hw_params)
{
        struct snd_usb_substream *subs = substream->runtime->private_data;

        return snd_usb_hw_params(subs, hw_params);
}

int snd_usb_hw_free(struct snd_usb_substream *subs)
{
        struct snd_usb_audio *chip = subs->stream->chip;

        snd_media_stop_pipeline(subs);
        scoped_guard(mutex, &chip->mutex) {
                subs->cur_audiofmt = NULL;
        }
        CLASS(snd_usb_lock, pm)(chip);
        if (!pm.err) {
                if (stop_endpoints(subs, false))
                        sync_pending_stops(subs);
                close_endpoints(chip, subs);
        }

        return 0;
}
EXPORT_SYMBOL_GPL(snd_usb_hw_free);

/*
 * hw_free callback
 *
 * reset the audio format and release the buffer
 */
static int snd_usb_pcm_hw_free(struct snd_pcm_substream *substream)
{
        struct snd_usb_substream *subs = substream->runtime->private_data;

        return snd_usb_hw_free(subs);
}

/* free-wheeling mode? (e.g. dmix) */
static int in_free_wheeling_mode(struct snd_pcm_runtime *runtime)
{
        return runtime->stop_threshold > runtime->buffer_size;
}

/* check whether early start is needed for playback stream */
static int lowlatency_playback_available(struct snd_pcm_runtime *runtime,
                                         struct snd_usb_substream *subs)
{
        struct snd_usb_audio *chip = subs->stream->chip;

        if (subs->direction == SNDRV_PCM_STREAM_CAPTURE)
                return false;
        /* disabled via module option? */
        if (!chip->lowlatency)
                return false;
        if (in_free_wheeling_mode(runtime))
                return false;
        /* implicit feedback mode has own operation mode */
        if (snd_usb_endpoint_implicit_feedback_sink(subs->data_endpoint))
                return false;
        return true;
}

/*
 * prepare callback
 *
 * only a few subtle things...
 */
static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
{
        struct snd_pcm_runtime *runtime = substream->runtime;
        struct snd_usb_substream *subs = runtime->private_data;
        struct snd_usb_audio *chip = subs->stream->chip;
        int retry = 0;
        int ret;

        CLASS(snd_usb_lock, pm)(chip);
        if (pm.err < 0)
                return pm.err;
        if (snd_BUG_ON(!subs->data_endpoint))
                return -EIO;

        ret = snd_usb_pcm_change_state(subs, UAC3_PD_STATE_D0);
        if (ret < 0)
                return ret;

 again:
        if (subs->sync_endpoint) {
                ret = snd_usb_endpoint_prepare(chip, subs->sync_endpoint);
                if (ret < 0)
                        return ret;
        }

        ret = snd_usb_endpoint_prepare(chip, subs->data_endpoint);
        if (ret < 0)
                return ret;
        else if (ret > 0)
                snd_usb_set_format_quirk(subs, subs->cur_audiofmt);
        ret = 0;

        /* reset the pointer */
        subs->buffer_bytes = frames_to_bytes(runtime, runtime->buffer_size);
        subs->inflight_bytes = 0;
        subs->hwptr_done = 0;
        subs->transfer_done = 0;
        subs->last_frame_number = 0;
        subs->period_elapsed_pending = 0;
        runtime->delay = 0;

        subs->lowlatency_playback = lowlatency_playback_available(runtime, subs);
        if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
            !subs->lowlatency_playback) {
                ret = start_endpoints(subs);
                /* if XRUN happens at starting streams (possibly with implicit
                 * fb case), restart again, but only try once.
                 */
                if (ret == -EPIPE && !retry++) {
                        sync_pending_stops(subs);
                        goto again;
                }
        }

        return ret;
}

/*
 * h/w constraints
 */

#ifdef HW_CONST_DEBUG
#define hwc_debug(fmt, args...) pr_debug(fmt, ##args)
#else
#define hwc_debug(fmt, args...) do { } while(0)
#endif

static const struct snd_pcm_hardware snd_usb_hardware =
{
        .info =                 SNDRV_PCM_INFO_MMAP |
                                SNDRV_PCM_INFO_MMAP_VALID |
                                SNDRV_PCM_INFO_BATCH |
                                SNDRV_PCM_INFO_INTERLEAVED |
                                SNDRV_PCM_INFO_BLOCK_TRANSFER |
                                SNDRV_PCM_INFO_PAUSE,
        .channels_min =         1,
        .channels_max =         256,
        .buffer_bytes_max =     INT_MAX, /* limited by BUFFER_TIME later */
        .period_bytes_min =     64,
        .period_bytes_max =     INT_MAX, /* limited by PERIOD_TIME later */
        .periods_min =          2,
        .periods_max =          1024,
};

static int hw_check_valid_format(struct snd_usb_substream *subs,
                                 struct snd_pcm_hw_params *params,
                                 const struct audioformat *fp)
{
        struct snd_interval *it = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
        struct snd_interval *ct = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
        struct snd_mask *fmts = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
        struct snd_interval *pt = hw_param_interval(params, SNDRV_PCM_HW_PARAM_PERIOD_TIME);
        struct snd_mask check_fmts;
        unsigned int ptime;

        /* check the format */
        snd_mask_none(&check_fmts);
        check_fmts.bits[0] = (u32)fp->formats;
        check_fmts.bits[1] = (u32)(fp->formats >> 32);
        snd_mask_intersect(&check_fmts, fmts);
        if (snd_mask_empty(&check_fmts)) {
                hwc_debug("   > check: no supported format 0x%llx\n", fp->formats);
                return 0;
        }
        /* check the channels */
        if (fp->channels < ct->min || fp->channels > ct->max) {
                hwc_debug("   > check: no valid channels %d (%d/%d)\n", fp->channels, ct->min, ct->max);
                return 0;
        }
        /* check the rate is within the range */
        if (fp->rate_min > it->max || (fp->rate_min == it->max && it->openmax)) {
                hwc_debug("   > check: rate_min %d > max %d\n", fp->rate_min, it->max);
                return 0;
        }
        if (fp->rate_max < it->min || (fp->rate_max == it->min && it->openmin)) {
                hwc_debug("   > check: rate_max %d < min %d\n", fp->rate_max, it->min);
                return 0;
        }
        /* check whether the period time is >= the data packet interval */
        if (subs->speed != USB_SPEED_FULL) {
                ptime = 125 * (1 << fp->datainterval);
                if (ptime > pt->max || (ptime == pt->max && pt->openmax)) {
                        hwc_debug("   > check: ptime %u > max %u\n", ptime, pt->max);
                        return 0;
                }
        }
        return 1;
}

static int apply_hw_params_minmax(struct snd_interval *it, unsigned int rmin,
                                  unsigned int rmax)
{
        int changed;

        if (rmin > rmax) {
                hwc_debug("  --> get empty\n");
                it->empty = 1;
                return -EINVAL;
        }

        changed = 0;
        if (it->min < rmin) {
                it->min = rmin;
                it->openmin = 0;
                changed = 1;
        }
        if (it->max > rmax) {
                it->max = rmax;
                it->openmax = 0;
                changed = 1;
        }
        if (snd_interval_checkempty(it)) {
                it->empty = 1;
                return -EINVAL;
        }
        hwc_debug("  --> (%d, %d) (changed = %d)\n", it->min, it->max, changed);
        return changed;
}

/* get the specified endpoint object that is being used by other streams
 * (i.e. the parameter is locked)
 */
static const struct snd_usb_endpoint *
get_endpoint_in_use(struct snd_usb_audio *chip, int endpoint,
                    const struct snd_usb_endpoint *ref_ep)
{
        const struct snd_usb_endpoint *ep;

        ep = snd_usb_get_endpoint(chip, endpoint);
        if (ep && ep->cur_audiofmt && (ep != ref_ep || ep->opened > 1))
                return ep;
        return NULL;
}

static int hw_rule_rate(struct snd_pcm_hw_params *params,
                        struct snd_pcm_hw_rule *rule)
{
        struct snd_usb_substream *subs = rule->private;
        struct snd_usb_audio *chip = subs->stream->chip;
        const struct snd_usb_endpoint *ep;
        const struct audioformat *fp;
        struct snd_interval *it = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
        unsigned int rmin, rmax, r;
        int i;

        hwc_debug("hw_rule_rate: (%d,%d)\n", it->min, it->max);
        rmin = UINT_MAX;
        rmax = 0;
        list_for_each_entry(fp, &subs->fmt_list, list) {
                if (!hw_check_valid_format(subs, params, fp))
                        continue;

                ep = get_endpoint_in_use(chip, fp->endpoint,
                                         subs->data_endpoint);
                if (ep) {
                        hwc_debug("rate limit %d for ep#%x\n",
                                  ep->cur_rate, fp->endpoint);
                        rmin = min(rmin, ep->cur_rate);
                        rmax = max(rmax, ep->cur_rate);
                        continue;
                }

                if (fp->implicit_fb) {
                        ep = get_endpoint_in_use(chip, fp->sync_ep,
                                                 subs->sync_endpoint);
                        if (ep) {
                                hwc_debug("rate limit %d for sync_ep#%x\n",
                                          ep->cur_rate, fp->sync_ep);
                                rmin = min(rmin, ep->cur_rate);
                                rmax = max(rmax, ep->cur_rate);
                                continue;
                        }
                }

                r = snd_usb_endpoint_get_clock_rate(chip, fp->clock);
                if (r > 0) {
                        if (!snd_interval_test(it, r))
                                continue;
                        rmin = min(rmin, r);
                        rmax = max(rmax, r);
                        continue;
                }
                if (fp->rate_table && fp->nr_rates) {
                        for (i = 0; i < fp->nr_rates; i++) {
                                r = fp->rate_table[i];
                                if (!snd_interval_test(it, r))
                                        continue;
                                rmin = min(rmin, r);
                                rmax = max(rmax, r);
                        }
                } else {
                        rmin = min(rmin, fp->rate_min);
                        rmax = max(rmax, fp->rate_max);
                }
        }

        return apply_hw_params_minmax(it, rmin, rmax);
}


static int hw_rule_channels(struct snd_pcm_hw_params *params,
                            struct snd_pcm_hw_rule *rule)
{
        struct snd_usb_substream *subs = rule->private;
        const struct audioformat *fp;
        struct snd_interval *it = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
        unsigned int rmin, rmax;

        hwc_debug("hw_rule_channels: (%d,%d)\n", it->min, it->max);
        rmin = UINT_MAX;
        rmax = 0;
        list_for_each_entry(fp, &subs->fmt_list, list) {
                if (!hw_check_valid_format(subs, params, fp))
                        continue;
                rmin = min(rmin, fp->channels);
                rmax = max(rmax, fp->channels);
        }

        return apply_hw_params_minmax(it, rmin, rmax);
}

static int apply_hw_params_format_bits(struct snd_mask *fmt, u64 fbits)
{
        u32 oldbits[2];
        int changed;

        oldbits[0] = fmt->bits[0];
        oldbits[1] = fmt->bits[1];
        fmt->bits[0] &= (u32)fbits;
        fmt->bits[1] &= (u32)(fbits >> 32);
        if (!fmt->bits[0] && !fmt->bits[1]) {
                hwc_debug("  --> get empty\n");
                return -EINVAL;
        }
        changed = (oldbits[0] != fmt->bits[0] || oldbits[1] != fmt->bits[1]);
        hwc_debug("  --> %x:%x (changed = %d)\n", fmt->bits[0], fmt->bits[1], changed);
        return changed;
}

static int hw_rule_format(struct snd_pcm_hw_params *params,
                          struct snd_pcm_hw_rule *rule)
{
        struct snd_usb_substream *subs = rule->private;
        struct snd_usb_audio *chip = subs->stream->chip;
        const struct snd_usb_endpoint *ep;
        const struct audioformat *fp;
        struct snd_mask *fmt = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
        u64 fbits;

        hwc_debug("hw_rule_format: %x:%x\n", fmt->bits[0], fmt->bits[1]);
        fbits = 0;
        list_for_each_entry(fp, &subs->fmt_list, list) {
                if (!hw_check_valid_format(subs, params, fp))
                        continue;

                ep = get_endpoint_in_use(chip, fp->endpoint,
                                         subs->data_endpoint);
                if (ep) {
                        hwc_debug("format limit %d for ep#%x\n",
                                  ep->cur_format, fp->endpoint);
                        fbits |= pcm_format_to_bits(ep->cur_format);
                        continue;
                }

                if (fp->implicit_fb) {
                        ep = get_endpoint_in_use(chip, fp->sync_ep,
                                                 subs->sync_endpoint);
                        if (ep) {
                                hwc_debug("format limit %d for sync_ep#%x\n",
                                          ep->cur_format, fp->sync_ep);
                                fbits |= pcm_format_to_bits(ep->cur_format);
                                continue;
                        }
                }

                fbits |= fp->formats;
        }
        return apply_hw_params_format_bits(fmt, fbits);
}

static int hw_rule_period_time(struct snd_pcm_hw_params *params,
                               struct snd_pcm_hw_rule *rule)
{
        struct snd_usb_substream *subs = rule->private;
        const struct audioformat *fp;
        struct snd_interval *it;
        unsigned char min_datainterval;
        unsigned int pmin;

        it = hw_param_interval(params, SNDRV_PCM_HW_PARAM_PERIOD_TIME);
        hwc_debug("hw_rule_period_time: (%u,%u)\n", it->min, it->max);
        min_datainterval = 0xff;
        list_for_each_entry(fp, &subs->fmt_list, list) {
                if (!hw_check_valid_format(subs, params, fp))
                        continue;
                min_datainterval = min(min_datainterval, fp->datainterval);
        }
        if (min_datainterval == 0xff) {
                hwc_debug("  --> get empty\n");
                it->empty = 1;
                return -EINVAL;
        }
        pmin = 125 * (1 << min_datainterval);

        return apply_hw_params_minmax(it, pmin, UINT_MAX);
}

/* additional hw constraints for implicit feedback mode */
static int hw_rule_period_size_implicit_fb(struct snd_pcm_hw_params *params,
                                           struct snd_pcm_hw_rule *rule)
{
        struct snd_usb_substream *subs = rule->private;
        struct snd_usb_audio *chip = subs->stream->chip;
        const struct audioformat *fp;
        const struct snd_usb_endpoint *ep;
        struct snd_interval *it;
        unsigned int rmin, rmax;

        it = hw_param_interval(params, SNDRV_PCM_HW_PARAM_PERIOD_SIZE);
        hwc_debug("hw_rule_period_size: (%u,%u)\n", it->min, it->max);
        rmin = UINT_MAX;
        rmax = 0;
        list_for_each_entry(fp, &subs->fmt_list, list) {
                if (!hw_check_valid_format(subs, params, fp))
                        continue;
                ep = get_endpoint_in_use(chip, fp->endpoint,
                                         subs->data_endpoint);
                if (ep) {
                        hwc_debug("period size limit %d for ep#%x\n",
                                  ep->cur_period_frames, fp->endpoint);
                        rmin = min(rmin, ep->cur_period_frames);
                        rmax = max(rmax, ep->cur_period_frames);
                        continue;
                }

                if (fp->implicit_fb) {
                        ep = get_endpoint_in_use(chip, fp->sync_ep,
                                                 subs->sync_endpoint);
                        if (ep) {
                                hwc_debug("period size limit %d for sync_ep#%x\n",
                                          ep->cur_period_frames, fp->sync_ep);
                                rmin = min(rmin, ep->cur_period_frames);
                                rmax = max(rmax, ep->cur_period_frames);
                                continue;
                        }
                }
        }

        if (!rmax)
                return 0; /* no limit by implicit fb */
        return apply_hw_params_minmax(it, rmin, rmax);
}

static int hw_rule_periods_implicit_fb(struct snd_pcm_hw_params *params,
                                       struct snd_pcm_hw_rule *rule)
{
        struct snd_usb_substream *subs = rule->private;
        struct snd_usb_audio *chip = subs->stream->chip;
        const struct audioformat *fp;
        const struct snd_usb_endpoint *ep;
        struct snd_interval *it;
        unsigned int rmin, rmax;

        it = hw_param_interval(params, SNDRV_PCM_HW_PARAM_PERIODS);
        hwc_debug("hw_rule_periods: (%u,%u)\n", it->min, it->max);
        rmin = UINT_MAX;
        rmax = 0;
        list_for_each_entry(fp, &subs->fmt_list, list) {
                if (!hw_check_valid_format(subs, params, fp))
                        continue;
                ep = get_endpoint_in_use(chip, fp->endpoint,
                                         subs->data_endpoint);
                if (ep) {
                        hwc_debug("periods limit %d for ep#%x\n",
                                  ep->cur_buffer_periods, fp->endpoint);
                        rmin = min(rmin, ep->cur_buffer_periods);
                        rmax = max(rmax, ep->cur_buffer_periods);
                        continue;
                }

                if (fp->implicit_fb) {
                        ep = get_endpoint_in_use(chip, fp->sync_ep,
                                                 subs->sync_endpoint);
                        if (ep) {
                                hwc_debug("periods limit %d for sync_ep#%x\n",
                                          ep->cur_buffer_periods, fp->sync_ep);
                                rmin = min(rmin, ep->cur_buffer_periods);
                                rmax = max(rmax, ep->cur_buffer_periods);
                                continue;
                        }
                }
        }

        if (!rmax)
                return 0; /* no limit by implicit fb */
        return apply_hw_params_minmax(it, rmin, rmax);
}

/*
 * set up the runtime hardware information.
 */

static int setup_hw_info(struct snd_pcm_runtime *runtime, struct snd_usb_substream *subs)
{
        const struct audioformat *fp;
        unsigned int pt, ptmin;
        int param_period_time_if_needed = -1;
        int err;

        runtime->hw.formats = subs->formats;

        runtime->hw.rate_min = 0x7fffffff;
        runtime->hw.rate_max = 0;
        runtime->hw.channels_min = 256;
        runtime->hw.channels_max = 0;
        runtime->hw.rates = 0;
        ptmin = UINT_MAX;
        /* check min/max rates and channels */
        list_for_each_entry(fp, &subs->fmt_list, list) {
                runtime->hw.rates |= fp->rates;
                if (runtime->hw.rate_min > fp->rate_min)
                        runtime->hw.rate_min = fp->rate_min;
                if (runtime->hw.rate_max < fp->rate_max)
                        runtime->hw.rate_max = fp->rate_max;
                if (runtime->hw.channels_min > fp->channels)
                        runtime->hw.channels_min = fp->channels;
                if (runtime->hw.channels_max < fp->channels)
                        runtime->hw.channels_max = fp->channels;
                if (fp->fmt_type == UAC_FORMAT_TYPE_II && fp->frame_size > 0) {
                        /* FIXME: there might be more than one audio formats... */
                        runtime->hw.period_bytes_min = runtime->hw.period_bytes_max =
                                fp->frame_size;
                }
                pt = 125 * (1 << fp->datainterval);
                ptmin = min(ptmin, pt);
        }

        param_period_time_if_needed = SNDRV_PCM_HW_PARAM_PERIOD_TIME;
        if (subs->speed == USB_SPEED_FULL)
                /* full speed devices have fixed data packet interval */
                ptmin = 1000;
        if (ptmin == 1000)
                /* if period time doesn't go below 1 ms, no rules needed */
                param_period_time_if_needed = -1;

        err = snd_pcm_hw_constraint_minmax(runtime,
                                           SNDRV_PCM_HW_PARAM_PERIOD_TIME,
                                           ptmin, UINT_MAX);
        if (err < 0)
                return err;

        err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
                                  hw_rule_rate, subs,
                                  SNDRV_PCM_HW_PARAM_RATE,
                                  SNDRV_PCM_HW_PARAM_FORMAT,
                                  SNDRV_PCM_HW_PARAM_CHANNELS,
                                  param_period_time_if_needed,
                                  -1);
        if (err < 0)
                return err;

        err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
                                  hw_rule_channels, subs,
                                  SNDRV_PCM_HW_PARAM_CHANNELS,
                                  SNDRV_PCM_HW_PARAM_FORMAT,
                                  SNDRV_PCM_HW_PARAM_RATE,
                                  param_period_time_if_needed,
                                  -1);
        if (err < 0)
                return err;
        err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
                                  hw_rule_format, subs,
                                  SNDRV_PCM_HW_PARAM_FORMAT,
                                  SNDRV_PCM_HW_PARAM_RATE,
                                  SNDRV_PCM_HW_PARAM_CHANNELS,
                                  param_period_time_if_needed,
                                  -1);
        if (err < 0)
                return err;
        if (param_period_time_if_needed >= 0) {
                err = snd_pcm_hw_rule_add(runtime, 0,
                                          SNDRV_PCM_HW_PARAM_PERIOD_TIME,
                                          hw_rule_period_time, subs,
                                          SNDRV_PCM_HW_PARAM_FORMAT,
                                          SNDRV_PCM_HW_PARAM_CHANNELS,
                                          SNDRV_PCM_HW_PARAM_RATE,
                                          -1);
                if (err < 0)
                        return err;
        }

        /* set max period and buffer sizes for 1 and 2 seconds, respectively */
        err = snd_pcm_hw_constraint_minmax(runtime,
                                           SNDRV_PCM_HW_PARAM_PERIOD_TIME,
                                           0, 1000000);
        if (err < 0)
                return err;
        err = snd_pcm_hw_constraint_minmax(runtime,
                                           SNDRV_PCM_HW_PARAM_BUFFER_TIME,
                                           0, 2000000);
        if (err < 0)
                return err;

        /* additional hw constraints for implicit fb */
        err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_SIZE,
                                  hw_rule_period_size_implicit_fb, subs,
                                  SNDRV_PCM_HW_PARAM_PERIOD_SIZE, -1);
        if (err < 0)
                return err;
        err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_PERIODS,
                                  hw_rule_periods_implicit_fb, subs,
                                  SNDRV_PCM_HW_PARAM_PERIODS, -1);
        if (err < 0)
                return err;

        list_for_each_entry(fp, &subs->fmt_list, list) {
                if (fp->implicit_fb) {
                        runtime->hw.info |= SNDRV_PCM_INFO_JOINT_DUPLEX;
                        break;
                }
        }

        return 0;
}

static int snd_usb_pcm_open(struct snd_pcm_substream *substream)
{
        int direction = substream->stream;
        struct snd_usb_stream *as = snd_pcm_substream_chip(substream);
        struct snd_pcm_runtime *runtime = substream->runtime;
        struct snd_usb_substream *subs = &as->substream[direction];
        struct snd_usb_audio *chip = subs->stream->chip;
        int ret;

        scoped_guard(mutex, &chip->mutex) {
                if (subs->opened)
                        return -EBUSY;
                subs->opened = 1;
        }

        runtime->hw = snd_usb_hardware;
        /* need an explicit sync to catch applptr update in low-latency mode */
        if (direction == SNDRV_PCM_STREAM_PLAYBACK &&
            as->chip->lowlatency)
                runtime->hw.info |= SNDRV_PCM_INFO_SYNC_APPLPTR;
        runtime->private_data = subs;
        subs->pcm_substream = substream;
        /* runtime PM is also done there */

        /* initialize DSD/DOP context */
        subs->dsd_dop.byte_idx = 0;
        subs->dsd_dop.channel = 0;
        subs->dsd_dop.marker = 1;

        ret = setup_hw_info(runtime, subs);
        if (ret < 0)
                goto err_open;
        ret = snd_usb_autoresume(subs->stream->chip);
        if (ret < 0)
                goto err_open;
        ret = snd_media_stream_init(subs, as->pcm, direction);
        if (ret < 0)
                goto err_resume;

        return 0;

err_resume:
        snd_usb_autosuspend(subs->stream->chip);
err_open:
        scoped_guard(mutex, &chip->mutex) {
                subs->opened = 0;
        }

        return ret;
}

static int snd_usb_pcm_close(struct snd_pcm_substream *substream)
{
        int direction = substream->stream;
        struct snd_usb_stream *as = snd_pcm_substream_chip(substream);
        struct snd_usb_substream *subs = &as->substream[direction];
        struct snd_usb_audio *chip = subs->stream->chip;
        int ret;

        snd_media_stop_pipeline(subs);

        {
                CLASS(snd_usb_lock, pm)(subs->stream->chip);
                if (pm.err)
                        return pm.err;
                ret = snd_usb_pcm_change_state(subs, UAC3_PD_STATE_D1);
                if (ret < 0)
                        return ret;
        }

        subs->pcm_substream = NULL;
        snd_usb_autosuspend(subs->stream->chip);
        scoped_guard(mutex, &chip->mutex) {
                subs->opened = 0;
        }

        return 0;
}

/* Since a URB can handle only a single linear buffer, we must use double
 * buffering when the data to be transferred overflows the buffer boundary.
 * To avoid inconsistencies when updating hwptr_done, we use double buffering
 * for all URBs.
 */
static void retire_capture_urb(struct snd_usb_substream *subs,
                               struct urb *urb)
{
        struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
        unsigned int stride, frames, bytes, oldptr;
        int i, period_elapsed = 0;
        unsigned char *cp;
        int current_frame_number;

        /* read frame number here, update pointer in critical section */
        current_frame_number = usb_get_current_frame_number(subs->dev);

        stride = runtime->frame_bits >> 3;

        for (i = 0; i < urb->number_of_packets; i++) {
                cp = (unsigned char *)urb->transfer_buffer + urb->iso_frame_desc[i].offset + subs->pkt_offset_adj;
                if (urb->iso_frame_desc[i].status)
                        dev_dbg_ratelimited(&subs->dev->dev,
                                            "frame %d active: %d\n", i,
                                            urb->iso_frame_desc[i].status);
                bytes = urb->iso_frame_desc[i].actual_length;
                if (subs->stream_offset_adj > 0) {
                        unsigned int adj = min(subs->stream_offset_adj, bytes);
                        cp += adj;
                        bytes -= adj;
                        subs->stream_offset_adj -= adj;
                }
                frames = bytes / stride;
                if (!subs->txfr_quirk)
                        bytes = frames * stride;
                if (bytes % (runtime->sample_bits >> 3) != 0) {
                        int oldbytes = bytes;
                        bytes = frames * stride;
                        dev_warn_ratelimited(&subs->dev->dev,
                                 "Corrected urb data len. %d->%d\n",
                                                        oldbytes, bytes);
                }
                /* update the current pointer */
                scoped_guard(spinlock_irqsave, &subs->lock) {
                        oldptr = subs->hwptr_done;
                        subs->hwptr_done += bytes;
                        if (subs->hwptr_done >= subs->buffer_bytes)
                                subs->hwptr_done -= subs->buffer_bytes;
                        frames = (bytes + (oldptr % stride)) / stride;
                        subs->transfer_done += frames;
                        if (subs->transfer_done >= runtime->period_size) {
                                subs->transfer_done -= runtime->period_size;
                                period_elapsed = 1;
                        }

                        /* realign last_frame_number */
                        subs->last_frame_number = current_frame_number;
                }
                /* copy a data chunk */
                if (oldptr + bytes > subs->buffer_bytes) {
                        unsigned int bytes1 = subs->buffer_bytes - oldptr;

                        memcpy(runtime->dma_area + oldptr, cp, bytes1);
                        memcpy(runtime->dma_area, cp + bytes1, bytes - bytes1);
                } else {
                        memcpy(runtime->dma_area + oldptr, cp, bytes);
                }
        }

        if (period_elapsed)
                snd_pcm_period_elapsed(subs->pcm_substream);
}

static void urb_ctx_queue_advance(struct snd_usb_substream *subs,
                                  struct urb *urb, unsigned int bytes)
{
        struct snd_urb_ctx *ctx = urb->context;

        ctx->queued += bytes;
        subs->inflight_bytes += bytes;
        subs->hwptr_done += bytes;
        if (subs->hwptr_done >= subs->buffer_bytes)
                subs->hwptr_done -= subs->buffer_bytes;
}

static inline void fill_playback_urb_dsd_dop(struct snd_usb_substream *subs,
                                             struct urb *urb, unsigned int bytes)
{
        struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
        unsigned int dst_idx = 0;
        unsigned int src_idx = subs->hwptr_done;
        unsigned int wrap = subs->buffer_bytes;
        u8 *dst = urb->transfer_buffer;
        u8 *src = runtime->dma_area;
        static const u8 marker[] = { 0x05, 0xfa };
        unsigned int queued = 0;

        /*
         * The DSP DOP format defines a way to transport DSD samples over
         * normal PCM data endpoints. It requires stuffing of marker bytes
         * (0x05 and 0xfa, alternating per sample frame), and then expects
         * 2 additional bytes of actual payload. The whole frame is stored
         * LSB.
         *
         * Hence, for a stereo transport, the buffer layout looks like this,
         * where L refers to left channel samples and R to right.
         *
         *   L1 L2 0x05   R1 R2 0x05   L3 L4 0xfa  R3 R4 0xfa
         *   L5 L6 0x05   R5 R6 0x05   L7 L8 0xfa  R7 R8 0xfa
         *   .....
         *
         */

        while (bytes--) {
                if (++subs->dsd_dop.byte_idx == 3) {
                        /* frame boundary? */
                        dst[dst_idx++] = marker[subs->dsd_dop.marker];
                        src_idx += 2;
                        subs->dsd_dop.byte_idx = 0;

                        if (++subs->dsd_dop.channel % runtime->channels == 0) {
                                /* alternate the marker */
                                subs->dsd_dop.marker++;
                                subs->dsd_dop.marker %= ARRAY_SIZE(marker);
                                subs->dsd_dop.channel = 0;
                        }
                } else {
                        /* stuff the DSD payload */
                        int idx = (src_idx + subs->dsd_dop.byte_idx - 1) % wrap;

                        if (subs->cur_audiofmt->dsd_bitrev)
                                dst[dst_idx++] = bitrev8(src[idx]);
                        else
                                dst[dst_idx++] = src[idx];
                        queued++;
                }
        }

        urb_ctx_queue_advance(subs, urb, queued);
}

/* copy bit-reversed bytes onto transfer buffer */
static void fill_playback_urb_dsd_bitrev(struct snd_usb_substream *subs,
                                         struct urb *urb, unsigned int bytes)
{
        struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
        const u8 *src = runtime->dma_area;
        u8 *buf = urb->transfer_buffer;
        int i, ofs = subs->hwptr_done;

        for (i = 0; i < bytes; i++) {
                *buf++ = bitrev8(src[ofs]);
                if (++ofs >= subs->buffer_bytes)
                        ofs = 0;
        }

        urb_ctx_queue_advance(subs, urb, bytes);
}

static void copy_to_urb(struct snd_usb_substream *subs, struct urb *urb,
                        int offset, int stride, unsigned int bytes)
{
        struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;

        if (subs->hwptr_done + bytes > subs->buffer_bytes) {
                /* err, the transferred area goes over buffer boundary. */
                unsigned int bytes1 = subs->buffer_bytes - subs->hwptr_done;

                memcpy(urb->transfer_buffer + offset,
                       runtime->dma_area + subs->hwptr_done, bytes1);
                memcpy(urb->transfer_buffer + offset + bytes1,
                       runtime->dma_area, bytes - bytes1);
        } else {
                memcpy(urb->transfer_buffer + offset,
                       runtime->dma_area + subs->hwptr_done, bytes);
        }

        urb_ctx_queue_advance(subs, urb, bytes);
}

static unsigned int copy_to_urb_quirk(struct snd_usb_substream *subs,
                                      struct urb *urb, int stride,
                                      unsigned int bytes)
{
        __le32 packet_length;
        int i;

        /* Put __le32 length descriptor at start of each packet. */
        for (i = 0; i < urb->number_of_packets; i++) {
                unsigned int length = urb->iso_frame_desc[i].length;
                unsigned int offset = urb->iso_frame_desc[i].offset;

                packet_length = cpu_to_le32(length);
                offset += i * sizeof(packet_length);
                urb->iso_frame_desc[i].offset = offset;
                urb->iso_frame_desc[i].length += sizeof(packet_length);
                memcpy(urb->transfer_buffer + offset,
                       &packet_length, sizeof(packet_length));
                copy_to_urb(subs, urb, offset + sizeof(packet_length),
                            stride, length);
        }
        /* Adjust transfer size accordingly. */
        bytes += urb->number_of_packets * sizeof(packet_length);
        return bytes;
}

static int prepare_playback_urb(struct snd_usb_substream *subs,
                                struct urb *urb,
                                bool in_stream_lock)
{
        struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
        struct snd_usb_endpoint *ep = subs->data_endpoint;
        struct snd_urb_ctx *ctx = urb->context;
        unsigned int frames, bytes;
        int counts;
        unsigned int transfer_done, frame_limit, avail = 0;
        int i, stride, period_elapsed = 0;

        stride = ep->stride;

        frames = 0;
        ctx->queued = 0;
        urb->number_of_packets = 0;

        scoped_guard(spinlock_irqsave, &subs->lock) {
                frame_limit = subs->frame_limit + ep->max_urb_frames;
                transfer_done = subs->transfer_done;

                if (subs->lowlatency_playback &&
                    runtime->state != SNDRV_PCM_STATE_DRAINING) {
                        unsigned int hwptr = subs->hwptr_done / stride;

                        /* calculate the byte offset-in-buffer of the appl_ptr */
                        avail = (runtime->control->appl_ptr - runtime->hw_ptr_base)
                                % runtime->buffer_size;
                        if (avail <= hwptr)
                                avail += runtime->buffer_size;
                        avail -= hwptr;
                }

                for (i = 0; i < ctx->packets; i++) {
                        counts = snd_usb_endpoint_next_packet_size(ep, ctx, i, avail);
                        if (counts < 0 ||
                            (frames + counts) * stride > ctx->buffer_size)
                                break;
                        /* set up descriptor */
                        urb->iso_frame_desc[i].offset = frames * stride;
                        urb->iso_frame_desc[i].length = counts * stride;
                        frames += counts;
                        avail -= counts;
                        urb->number_of_packets++;
                        transfer_done += counts;
                        if (transfer_done >= runtime->period_size) {
                                transfer_done -= runtime->period_size;
                                frame_limit = 0;
                                period_elapsed = 1;
                                if (subs->fmt_type == UAC_FORMAT_TYPE_II) {
                                        if (transfer_done > 0) {
                                                /* FIXME: fill-max mode is not
                                                 * supported yet */
                                                frames -= transfer_done;
                                                counts -= transfer_done;
                                                urb->iso_frame_desc[i].length =
                                                        counts * stride;
                                                transfer_done = 0;
                                        }
                                        i++;
                                        if (i < ctx->packets) {
                                                /* add a transfer delimiter */
                                                urb->iso_frame_desc[i].offset =
                                                        frames * stride;
                                                urb->iso_frame_desc[i].length = 0;
                                                urb->number_of_packets++;
                                        }
                                        break;
                                }
                        }
                        /* finish at the period boundary or after enough frames */
                        if ((period_elapsed || transfer_done >= frame_limit) &&
                            !snd_usb_endpoint_implicit_feedback_sink(ep))
                                break;
                }

                if (!frames)
                        return -EAGAIN;

                bytes = frames * stride;
                subs->transfer_done = transfer_done;
                subs->frame_limit = frame_limit;
                if (unlikely(ep->cur_format == SNDRV_PCM_FORMAT_DSD_U16_LE &&
                             subs->cur_audiofmt->dsd_dop)) {
                        fill_playback_urb_dsd_dop(subs, urb, bytes);
                } else if (unlikely(ep->cur_format == SNDRV_PCM_FORMAT_DSD_U8 &&
                                    subs->cur_audiofmt->dsd_bitrev)) {
                        fill_playback_urb_dsd_bitrev(subs, urb, bytes);
                } else {
                        /* usual PCM */
                        if (!subs->tx_length_quirk)
                                copy_to_urb(subs, urb, 0, stride, bytes);
                        else
                                bytes = copy_to_urb_quirk(subs, urb, stride, bytes);
                        /* bytes is now amount of outgoing data */
                }

                subs->last_frame_number = usb_get_current_frame_number(subs->dev);

                if (subs->trigger_tstamp_pending_update) {
                        /* this is the first actual URB submitted,
                         * update trigger timestamp to reflect actual start time
                         */
                        snd_pcm_gettime(runtime, &runtime->trigger_tstamp);
                        subs->trigger_tstamp_pending_update = false;
                }

                if (period_elapsed && !subs->running && subs->lowlatency_playback) {
                        subs->period_elapsed_pending = 1;
                        period_elapsed = 0;
                }
        }

        urb->transfer_buffer_length = bytes;
        if (period_elapsed) {
                if (in_stream_lock)
                        snd_pcm_period_elapsed_under_stream_lock(subs->pcm_substream);
                else
                        snd_pcm_period_elapsed(subs->pcm_substream);
        }
        return 0;
}

/*
 * process after playback data complete
 * - decrease the delay count again
 */
static void retire_playback_urb(struct snd_usb_substream *subs,
                               struct urb *urb)
{
        struct snd_urb_ctx *ctx = urb->context;
        bool period_elapsed = false;

        scoped_guard(spinlock_irqsave, &subs->lock) {
                if (ctx->queued) {
                        if (subs->inflight_bytes >= ctx->queued)
                                subs->inflight_bytes -= ctx->queued;
                        else
                                subs->inflight_bytes = 0;
                }

                subs->last_frame_number = usb_get_current_frame_number(subs->dev);
                if (subs->running) {
                        period_elapsed = subs->period_elapsed_pending;
                        subs->period_elapsed_pending = 0;
                }
        }
        if (period_elapsed)
                snd_pcm_period_elapsed(subs->pcm_substream);
}

/* PCM ack callback for the playback stream;
 * this plays a role only when the stream is running in low-latency mode.
 */
static int snd_usb_pcm_playback_ack(struct snd_pcm_substream *substream)
{
        struct snd_usb_substream *subs = substream->runtime->private_data;
        struct snd_usb_endpoint *ep;

        if (!subs->lowlatency_playback || !subs->running)
                return 0;
        ep = subs->data_endpoint;
        if (!ep)
                return 0;
        /* When no more in-flight URBs available, try to process the pending
         * outputs here
         */
        if (!ep->active_mask)
                return snd_usb_queue_pending_output_urbs(ep, true);
        return 0;
}

static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substream,
                                              int cmd)
{
        struct snd_usb_substream *subs = substream->runtime->private_data;
        int err;

        switch (cmd) {
        case SNDRV_PCM_TRIGGER_START:
                subs->trigger_tstamp_pending_update = true;
                fallthrough;
        case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
                snd_usb_endpoint_set_callback(subs->data_endpoint,
                                              prepare_playback_urb,
                                              retire_playback_urb,
                                              subs);
                if (subs->lowlatency_playback &&
                    cmd == SNDRV_PCM_TRIGGER_START) {
                        if (in_free_wheeling_mode(substream->runtime))
                                subs->lowlatency_playback = false;
                        err = start_endpoints(subs);
                        if (err < 0) {
                                snd_usb_endpoint_set_callback(subs->data_endpoint,
                                                              NULL, NULL, NULL);
                                return err;
                        }
                }
                subs->running = 1;
                dev_dbg(&subs->dev->dev, "%d:%d Start Playback PCM\n",
                        subs->cur_audiofmt->iface,
                        subs->cur_audiofmt->altsetting);
                return 0;
        case SNDRV_PCM_TRIGGER_SUSPEND:
        case SNDRV_PCM_TRIGGER_STOP:
                stop_endpoints(subs, substream->runtime->state == SNDRV_PCM_STATE_DRAINING);
                snd_usb_endpoint_set_callback(subs->data_endpoint,
                                              NULL, NULL, NULL);
                subs->running = 0;
                dev_dbg(&subs->dev->dev, "%d:%d Stop Playback PCM\n",
                        subs->cur_audiofmt->iface,
                        subs->cur_audiofmt->altsetting);
                return 0;
        case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
                /* keep retire_data_urb for delay calculation */
                snd_usb_endpoint_set_callback(subs->data_endpoint,
                                              NULL,
                                              retire_playback_urb,
                                              subs);
                subs->running = 0;
                dev_dbg(&subs->dev->dev, "%d:%d Pause Playback PCM\n",
                        subs->cur_audiofmt->iface,
                        subs->cur_audiofmt->altsetting);
                return 0;
        }

        return -EINVAL;
}

static int snd_usb_substream_capture_trigger(struct snd_pcm_substream *substream,
                                             int cmd)
{
        int err;
        struct snd_usb_substream *subs = substream->runtime->private_data;

        switch (cmd) {
        case SNDRV_PCM_TRIGGER_START:
                err = start_endpoints(subs);
                if (err < 0)
                        return err;
                fallthrough;
        case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
                snd_usb_endpoint_set_callback(subs->data_endpoint,
                                              NULL, retire_capture_urb,
                                              subs);
                subs->last_frame_number = usb_get_current_frame_number(subs->dev);
                subs->running = 1;
                dev_dbg(&subs->dev->dev, "%d:%d Start Capture PCM\n",
                        subs->cur_audiofmt->iface,
                        subs->cur_audiofmt->altsetting);
                return 0;
        case SNDRV_PCM_TRIGGER_SUSPEND:
        case SNDRV_PCM_TRIGGER_STOP:
                stop_endpoints(subs, false);
                fallthrough;
        case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
                snd_usb_endpoint_set_callback(subs->data_endpoint,
                                              NULL, NULL, NULL);
                subs->running = 0;
                dev_dbg(&subs->dev->dev, "%d:%d Stop Capture PCM\n",
                        subs->cur_audiofmt->iface,
                        subs->cur_audiofmt->altsetting);
                return 0;
        }

        return -EINVAL;
}

static const struct snd_pcm_ops snd_usb_playback_ops = {
        .open =         snd_usb_pcm_open,
        .close =        snd_usb_pcm_close,
        .hw_params =    snd_usb_pcm_hw_params,
        .hw_free =      snd_usb_pcm_hw_free,
        .prepare =      snd_usb_pcm_prepare,
        .trigger =      snd_usb_substream_playback_trigger,
        .sync_stop =    snd_usb_pcm_sync_stop,
        .pointer =      snd_usb_pcm_pointer,
        .ack =          snd_usb_pcm_playback_ack,
};

static const struct snd_pcm_ops snd_usb_capture_ops = {
        .open =         snd_usb_pcm_open,
        .close =        snd_usb_pcm_close,
        .hw_params =    snd_usb_pcm_hw_params,
        .hw_free =      snd_usb_pcm_hw_free,
        .prepare =      snd_usb_pcm_prepare,
        .trigger =      snd_usb_substream_capture_trigger,
        .sync_stop =    snd_usb_pcm_sync_stop,
        .pointer =      snd_usb_pcm_pointer,
};

void snd_usb_set_pcm_ops(struct snd_pcm *pcm, int stream)
{
        const struct snd_pcm_ops *ops;

        ops = stream == SNDRV_PCM_STREAM_PLAYBACK ?
                        &snd_usb_playback_ops : &snd_usb_capture_ops;
        snd_pcm_set_ops(pcm, stream, ops);
}

void snd_usb_preallocate_buffer(struct snd_usb_substream *subs)
{
        struct snd_pcm *pcm = subs->stream->pcm;
        struct snd_pcm_substream *s = pcm->streams[subs->direction].substream;
        struct device *dev = subs->dev->bus->sysdev;

        if (snd_usb_use_vmalloc)
                snd_pcm_set_managed_buffer(s, SNDRV_DMA_TYPE_VMALLOC,
                                           NULL, 0, 0);
        else
                snd_pcm_set_managed_buffer(s, SNDRV_DMA_TYPE_DEV_SG,
                                           dev, 64*1024, 512*1024);
}