root/drivers/net/wwan/qcom_bam_dmux.c
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Qualcomm BAM-DMUX WWAN network driver
 * Copyright (c) 2020, Stephan Gerhold <stephan@gerhold.net>
 */

#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/completion.h>
#include <linux/dma-mapping.h>
#include <linux/dmaengine.h>
#include <linux/if_arp.h>
#include <linux/interrupt.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
#include <linux/soc/qcom/smem_state.h>
#include <linux/spinlock.h>
#include <linux/wait.h>
#include <linux/workqueue.h>
#include <net/pkt_sched.h>

#define BAM_DMUX_BUFFER_SIZE            SZ_2K
#define BAM_DMUX_HDR_SIZE               sizeof(struct bam_dmux_hdr)
#define BAM_DMUX_MAX_DATA_SIZE          (BAM_DMUX_BUFFER_SIZE - BAM_DMUX_HDR_SIZE)
#define BAM_DMUX_NUM_SKB                32

#define BAM_DMUX_HDR_MAGIC              0x33fc

#define BAM_DMUX_AUTOSUSPEND_DELAY      1000
#define BAM_DMUX_REMOTE_TIMEOUT         msecs_to_jiffies(2000)

enum {
        BAM_DMUX_CMD_DATA,
        BAM_DMUX_CMD_OPEN,
        BAM_DMUX_CMD_CLOSE,
};

enum {
        BAM_DMUX_CH_DATA_0,
        BAM_DMUX_CH_DATA_1,
        BAM_DMUX_CH_DATA_2,
        BAM_DMUX_CH_DATA_3,
        BAM_DMUX_CH_DATA_4,
        BAM_DMUX_CH_DATA_5,
        BAM_DMUX_CH_DATA_6,
        BAM_DMUX_CH_DATA_7,
        BAM_DMUX_NUM_CH
};

struct bam_dmux_hdr {
        u16 magic;
        u8 signal;
        u8 cmd;
        u8 pad;
        u8 ch;
        u16 len;
};

struct bam_dmux_skb_dma {
        struct bam_dmux *dmux;
        struct sk_buff *skb;
        dma_addr_t addr;
};

struct bam_dmux {
        struct device *dev;

        int pc_irq;
        bool pc_state, pc_ack_state;
        struct qcom_smem_state *pc, *pc_ack;
        u32 pc_mask, pc_ack_mask;
        wait_queue_head_t pc_wait;
        struct completion pc_ack_completion;

        struct dma_chan *rx, *tx;
        struct bam_dmux_skb_dma rx_skbs[BAM_DMUX_NUM_SKB];
        struct bam_dmux_skb_dma tx_skbs[BAM_DMUX_NUM_SKB];
        spinlock_t tx_lock; /* Protect tx_skbs, tx_next_skb */
        unsigned int tx_next_skb;
        atomic_long_t tx_deferred_skb;
        struct work_struct tx_wakeup_work;

        DECLARE_BITMAP(remote_channels, BAM_DMUX_NUM_CH);
        struct work_struct register_netdev_work;
        struct net_device *netdevs[BAM_DMUX_NUM_CH];
};

struct bam_dmux_netdev {
        struct bam_dmux *dmux;
        u8 ch;
};

static void bam_dmux_pc_vote(struct bam_dmux *dmux, bool enable)
{
        reinit_completion(&dmux->pc_ack_completion);
        qcom_smem_state_update_bits(dmux->pc, dmux->pc_mask,
                                    enable ? dmux->pc_mask : 0);
}

static void bam_dmux_pc_ack(struct bam_dmux *dmux)
{
        qcom_smem_state_update_bits(dmux->pc_ack, dmux->pc_ack_mask,
                                    dmux->pc_ack_state ? 0 : dmux->pc_ack_mask);
        dmux->pc_ack_state = !dmux->pc_ack_state;
}

static bool bam_dmux_skb_dma_map(struct bam_dmux_skb_dma *skb_dma,
                                 enum dma_data_direction dir)
{
        struct device *dev = skb_dma->dmux->dev;

        skb_dma->addr = dma_map_single(dev, skb_dma->skb->data, skb_dma->skb->len, dir);
        if (dma_mapping_error(dev, skb_dma->addr)) {
                dev_err(dev, "Failed to DMA map buffer\n");
                skb_dma->addr = 0;
                return false;
        }

        return true;
}

static void bam_dmux_skb_dma_unmap(struct bam_dmux_skb_dma *skb_dma,
                                   enum dma_data_direction dir)
{
        dma_unmap_single(skb_dma->dmux->dev, skb_dma->addr, skb_dma->skb->len, dir);
        skb_dma->addr = 0;
}

static void bam_dmux_tx_wake_queues(struct bam_dmux *dmux)
{
        int i;

        dev_dbg(dmux->dev, "wake queues\n");

        for (i = 0; i < BAM_DMUX_NUM_CH; ++i) {
                struct net_device *netdev = dmux->netdevs[i];

                if (netdev && netif_running(netdev))
                        netif_wake_queue(netdev);
        }
}

static void bam_dmux_tx_stop_queues(struct bam_dmux *dmux)
{
        int i;

        dev_dbg(dmux->dev, "stop queues\n");

        for (i = 0; i < BAM_DMUX_NUM_CH; ++i) {
                struct net_device *netdev = dmux->netdevs[i];

                if (netdev)
                        netif_stop_queue(netdev);
        }
}

static void bam_dmux_tx_done(struct bam_dmux_skb_dma *skb_dma)
{
        struct bam_dmux *dmux = skb_dma->dmux;
        unsigned long flags;

        pm_runtime_put_autosuspend(dmux->dev);

        if (skb_dma->addr)
                bam_dmux_skb_dma_unmap(skb_dma, DMA_TO_DEVICE);

        spin_lock_irqsave(&dmux->tx_lock, flags);
        skb_dma->skb = NULL;
        if (skb_dma == &dmux->tx_skbs[dmux->tx_next_skb % BAM_DMUX_NUM_SKB])
                bam_dmux_tx_wake_queues(dmux);
        spin_unlock_irqrestore(&dmux->tx_lock, flags);
}

static void bam_dmux_tx_callback(void *data)
{
        struct bam_dmux_skb_dma *skb_dma = data;
        struct sk_buff *skb = skb_dma->skb;

        bam_dmux_tx_done(skb_dma);
        dev_consume_skb_any(skb);
}

static bool bam_dmux_skb_dma_submit_tx(struct bam_dmux_skb_dma *skb_dma)
{
        struct bam_dmux *dmux = skb_dma->dmux;
        struct dma_async_tx_descriptor *desc;

        desc = dmaengine_prep_slave_single(dmux->tx, skb_dma->addr,
                                           skb_dma->skb->len, DMA_MEM_TO_DEV,
                                           DMA_PREP_INTERRUPT);
        if (!desc) {
                dev_err(dmux->dev, "Failed to prepare TX DMA buffer\n");
                return false;
        }

        desc->callback = bam_dmux_tx_callback;
        desc->callback_param = skb_dma;
        desc->cookie = dmaengine_submit(desc);
        return true;
}

static struct bam_dmux_skb_dma *
bam_dmux_tx_queue(struct bam_dmux *dmux, struct sk_buff *skb)
{
        struct bam_dmux_skb_dma *skb_dma;
        unsigned long flags;

        spin_lock_irqsave(&dmux->tx_lock, flags);

        skb_dma = &dmux->tx_skbs[dmux->tx_next_skb % BAM_DMUX_NUM_SKB];
        if (skb_dma->skb) {
                bam_dmux_tx_stop_queues(dmux);
                spin_unlock_irqrestore(&dmux->tx_lock, flags);
                return NULL;
        }
        skb_dma->skb = skb;

        dmux->tx_next_skb++;
        if (dmux->tx_skbs[dmux->tx_next_skb % BAM_DMUX_NUM_SKB].skb)
                bam_dmux_tx_stop_queues(dmux);

        spin_unlock_irqrestore(&dmux->tx_lock, flags);
        return skb_dma;
}

static int bam_dmux_send_cmd(struct bam_dmux_netdev *bndev, u8 cmd)
{
        struct bam_dmux *dmux = bndev->dmux;
        struct bam_dmux_skb_dma *skb_dma;
        struct bam_dmux_hdr *hdr;
        struct sk_buff *skb;
        int ret;

        skb = alloc_skb(sizeof(*hdr), GFP_KERNEL);
        if (!skb)
                return -ENOMEM;

        hdr = skb_put_zero(skb, sizeof(*hdr));
        hdr->magic = BAM_DMUX_HDR_MAGIC;
        hdr->cmd = cmd;
        hdr->ch = bndev->ch;

        skb_dma = bam_dmux_tx_queue(dmux, skb);
        if (!skb_dma) {
                ret = -EAGAIN;
                goto free_skb;
        }

        ret = pm_runtime_get_sync(dmux->dev);
        if (ret < 0)
                goto tx_fail;

        if (!bam_dmux_skb_dma_map(skb_dma, DMA_TO_DEVICE)) {
                ret = -ENOMEM;
                goto tx_fail;
        }

        if (!bam_dmux_skb_dma_submit_tx(skb_dma)) {
                ret = -EIO;
                goto tx_fail;
        }

        dma_async_issue_pending(dmux->tx);
        return 0;

tx_fail:
        bam_dmux_tx_done(skb_dma);
free_skb:
        dev_kfree_skb(skb);
        return ret;
}

static int bam_dmux_netdev_open(struct net_device *netdev)
{
        struct bam_dmux_netdev *bndev = netdev_priv(netdev);
        int ret;

        ret = bam_dmux_send_cmd(bndev, BAM_DMUX_CMD_OPEN);
        if (ret)
                return ret;

        netif_start_queue(netdev);
        return 0;
}

static int bam_dmux_netdev_stop(struct net_device *netdev)
{
        struct bam_dmux_netdev *bndev = netdev_priv(netdev);

        netif_stop_queue(netdev);
        bam_dmux_send_cmd(bndev, BAM_DMUX_CMD_CLOSE);
        return 0;
}

static unsigned int needed_room(unsigned int avail, unsigned int needed)
{
        if (avail >= needed)
                return 0;
        return needed - avail;
}

static int bam_dmux_tx_prepare_skb(struct bam_dmux_netdev *bndev,
                                   struct sk_buff *skb)
{
        unsigned int head = needed_room(skb_headroom(skb), BAM_DMUX_HDR_SIZE);
        unsigned int pad = sizeof(u32) - skb->len % sizeof(u32);
        unsigned int tail = needed_room(skb_tailroom(skb), pad);
        struct bam_dmux_hdr *hdr;
        int ret;

        if (head || tail || skb_cloned(skb)) {
                ret = pskb_expand_head(skb, head, tail, GFP_ATOMIC);
                if (ret)
                        return ret;
        }

        hdr = skb_push(skb, sizeof(*hdr));
        hdr->magic = BAM_DMUX_HDR_MAGIC;
        hdr->signal = 0;
        hdr->cmd = BAM_DMUX_CMD_DATA;
        hdr->pad = pad;
        hdr->ch = bndev->ch;
        hdr->len = skb->len - sizeof(*hdr);
        if (pad)
                skb_put_zero(skb, pad);

        return 0;
}

static netdev_tx_t bam_dmux_netdev_start_xmit(struct sk_buff *skb,
                                              struct net_device *netdev)
{
        struct bam_dmux_netdev *bndev = netdev_priv(netdev);
        struct bam_dmux *dmux = bndev->dmux;
        struct bam_dmux_skb_dma *skb_dma;
        int active, ret;

        skb_dma = bam_dmux_tx_queue(dmux, skb);
        if (!skb_dma)
                return NETDEV_TX_BUSY;

        active = pm_runtime_get(dmux->dev);
        if (active < 0 && active != -EINPROGRESS)
                goto drop;

        ret = bam_dmux_tx_prepare_skb(bndev, skb);
        if (ret)
                goto drop;

        if (!bam_dmux_skb_dma_map(skb_dma, DMA_TO_DEVICE))
                goto drop;

        if (active <= 0) {
                /* Cannot sleep here so mark skb for wakeup handler and return */
                if (!atomic_long_fetch_or(BIT(skb_dma - dmux->tx_skbs),
                                          &dmux->tx_deferred_skb))
                        queue_pm_work(&dmux->tx_wakeup_work);
                return NETDEV_TX_OK;
        }

        if (!bam_dmux_skb_dma_submit_tx(skb_dma))
                goto drop;

        dma_async_issue_pending(dmux->tx);
        return NETDEV_TX_OK;

drop:
        bam_dmux_tx_done(skb_dma);
        dev_kfree_skb_any(skb);
        return NETDEV_TX_OK;
}

static void bam_dmux_tx_wakeup_work(struct work_struct *work)
{
        struct bam_dmux *dmux = container_of(work, struct bam_dmux, tx_wakeup_work);
        unsigned long pending;
        int ret, i;

        ret = pm_runtime_resume_and_get(dmux->dev);
        if (ret < 0) {
                dev_err(dmux->dev, "Failed to resume: %d\n", ret);
                return;
        }

        pending = atomic_long_xchg(&dmux->tx_deferred_skb, 0);
        if (!pending)
                goto out;

        dev_dbg(dmux->dev, "pending skbs after wakeup: %#lx\n", pending);
        for_each_set_bit(i, &pending, BAM_DMUX_NUM_SKB) {
                bam_dmux_skb_dma_submit_tx(&dmux->tx_skbs[i]);
        }
        dma_async_issue_pending(dmux->tx);

out:
        pm_runtime_put_autosuspend(dmux->dev);
}

static const struct net_device_ops bam_dmux_ops = {
        .ndo_open       = bam_dmux_netdev_open,
        .ndo_stop       = bam_dmux_netdev_stop,
        .ndo_start_xmit = bam_dmux_netdev_start_xmit,
};

static const struct device_type wwan_type = {
        .name = "wwan",
};

static void bam_dmux_netdev_setup(struct net_device *dev)
{
        dev->netdev_ops = &bam_dmux_ops;

        dev->type = ARPHRD_RAWIP;
        SET_NETDEV_DEVTYPE(dev, &wwan_type);
        dev->flags = IFF_POINTOPOINT | IFF_NOARP;

        dev->mtu = ETH_DATA_LEN;
        dev->max_mtu = BAM_DMUX_MAX_DATA_SIZE;
        dev->needed_headroom = sizeof(struct bam_dmux_hdr);
        dev->needed_tailroom = sizeof(u32); /* word-aligned */
        dev->tx_queue_len = DEFAULT_TX_QUEUE_LEN;

        /* This perm addr will be used as interface identifier by IPv6 */
        dev->addr_assign_type = NET_ADDR_RANDOM;
        eth_random_addr(dev->perm_addr);
}

static void bam_dmux_register_netdev_work(struct work_struct *work)
{
        struct bam_dmux *dmux = container_of(work, struct bam_dmux, register_netdev_work);
        struct bam_dmux_netdev *bndev;
        struct net_device *netdev;
        int ch, ret;

        for_each_set_bit(ch, dmux->remote_channels, BAM_DMUX_NUM_CH) {
                if (dmux->netdevs[ch])
                        continue;

                netdev = alloc_netdev(sizeof(*bndev), "wwan%d", NET_NAME_ENUM,
                                      bam_dmux_netdev_setup);
                if (!netdev)
                        return;

                SET_NETDEV_DEV(netdev, dmux->dev);
                netdev->dev_port = ch;

                bndev = netdev_priv(netdev);
                bndev->dmux = dmux;
                bndev->ch = ch;

                ret = register_netdev(netdev);
                if (ret) {
                        dev_err(dmux->dev, "Failed to register netdev for channel %u: %d\n",
                                ch, ret);
                        free_netdev(netdev);
                        return;
                }

                dmux->netdevs[ch] = netdev;
        }
}

static void bam_dmux_rx_callback(void *data);

static bool bam_dmux_skb_dma_submit_rx(struct bam_dmux_skb_dma *skb_dma)
{
        struct bam_dmux *dmux = skb_dma->dmux;
        struct dma_async_tx_descriptor *desc;

        desc = dmaengine_prep_slave_single(dmux->rx, skb_dma->addr,
                                           skb_dma->skb->len, DMA_DEV_TO_MEM,
                                           DMA_PREP_INTERRUPT);
        if (!desc) {
                dev_err(dmux->dev, "Failed to prepare RX DMA buffer\n");
                return false;
        }

        desc->callback = bam_dmux_rx_callback;
        desc->callback_param = skb_dma;
        desc->cookie = dmaengine_submit(desc);
        return true;
}

static bool bam_dmux_skb_dma_queue_rx(struct bam_dmux_skb_dma *skb_dma, gfp_t gfp)
{
        if (!skb_dma->skb) {
                skb_dma->skb = __netdev_alloc_skb(NULL, BAM_DMUX_BUFFER_SIZE, gfp);
                if (!skb_dma->skb)
                        return false;
                skb_put(skb_dma->skb, BAM_DMUX_BUFFER_SIZE);
        }

        return bam_dmux_skb_dma_map(skb_dma, DMA_FROM_DEVICE) &&
               bam_dmux_skb_dma_submit_rx(skb_dma);
}

static void bam_dmux_cmd_data(struct bam_dmux_skb_dma *skb_dma)
{
        struct bam_dmux *dmux = skb_dma->dmux;
        struct sk_buff *skb = skb_dma->skb;
        struct bam_dmux_hdr *hdr = (struct bam_dmux_hdr *)skb->data;
        struct net_device *netdev = dmux->netdevs[hdr->ch];

        if (!netdev || !netif_running(netdev)) {
                dev_warn(dmux->dev, "Data for inactive channel %u\n", hdr->ch);
                return;
        }

        if (hdr->len > BAM_DMUX_MAX_DATA_SIZE) {
                dev_err(dmux->dev, "Data larger than buffer? (%u > %u)\n",
                        hdr->len, (u16)BAM_DMUX_MAX_DATA_SIZE);
                return;
        }

        skb_dma->skb = NULL; /* Hand over to network stack */

        skb_pull(skb, sizeof(*hdr));
        skb_trim(skb, hdr->len);
        skb->dev = netdev;

        /* Only Raw-IP/QMAP is supported by this driver */
        switch (skb->data[0] & 0xf0) {
        case 0x40:
                skb->protocol = htons(ETH_P_IP);
                break;
        case 0x60:
                skb->protocol = htons(ETH_P_IPV6);
                break;
        default:
                skb->protocol = htons(ETH_P_MAP);
                break;
        }

        netif_receive_skb(skb);
}

static void bam_dmux_cmd_open(struct bam_dmux *dmux, struct bam_dmux_hdr *hdr)
{
        struct net_device *netdev = dmux->netdevs[hdr->ch];

        dev_dbg(dmux->dev, "open channel: %u\n", hdr->ch);

        if (__test_and_set_bit(hdr->ch, dmux->remote_channels)) {
                dev_warn(dmux->dev, "Channel already open: %u\n", hdr->ch);
                return;
        }

        if (netdev) {
                netif_device_attach(netdev);
        } else {
                /* Cannot sleep here, schedule work to register the netdev */
                schedule_work(&dmux->register_netdev_work);
        }
}

static void bam_dmux_cmd_close(struct bam_dmux *dmux, struct bam_dmux_hdr *hdr)
{
        struct net_device *netdev = dmux->netdevs[hdr->ch];

        dev_dbg(dmux->dev, "close channel: %u\n", hdr->ch);

        if (!__test_and_clear_bit(hdr->ch, dmux->remote_channels)) {
                dev_err(dmux->dev, "Channel not open: %u\n", hdr->ch);
                return;
        }

        if (netdev)
                netif_device_detach(netdev);
}

static void bam_dmux_rx_callback(void *data)
{
        struct bam_dmux_skb_dma *skb_dma = data;
        struct bam_dmux *dmux = skb_dma->dmux;
        struct sk_buff *skb = skb_dma->skb;
        struct bam_dmux_hdr *hdr = (struct bam_dmux_hdr *)skb->data;

        bam_dmux_skb_dma_unmap(skb_dma, DMA_FROM_DEVICE);

        if (hdr->magic != BAM_DMUX_HDR_MAGIC) {
                dev_err(dmux->dev, "Invalid magic in header: %#x\n", hdr->magic);
                goto out;
        }

        if (hdr->ch >= BAM_DMUX_NUM_CH) {
                dev_dbg(dmux->dev, "Unsupported channel: %u\n", hdr->ch);
                goto out;
        }

        switch (hdr->cmd) {
        case BAM_DMUX_CMD_DATA:
                bam_dmux_cmd_data(skb_dma);
                break;
        case BAM_DMUX_CMD_OPEN:
                bam_dmux_cmd_open(dmux, hdr);
                break;
        case BAM_DMUX_CMD_CLOSE:
                bam_dmux_cmd_close(dmux, hdr);
                break;
        default:
                dev_err(dmux->dev, "Unsupported command %u on channel %u\n",
                        hdr->cmd, hdr->ch);
                break;
        }

out:
        if (bam_dmux_skb_dma_queue_rx(skb_dma, GFP_ATOMIC))
                dma_async_issue_pending(dmux->rx);
}

static bool bam_dmux_power_on(struct bam_dmux *dmux)
{
        struct device *dev = dmux->dev;
        struct dma_slave_config dma_rx_conf = {
                .direction = DMA_DEV_TO_MEM,
                .src_maxburst = BAM_DMUX_BUFFER_SIZE,
        };
        int i;

        dmux->rx = dma_request_chan(dev, "rx");
        if (IS_ERR(dmux->rx)) {
                dev_err(dev, "Failed to request RX DMA channel: %pe\n", dmux->rx);
                dmux->rx = NULL;
                return false;
        }
        dmaengine_slave_config(dmux->rx, &dma_rx_conf);

        for (i = 0; i < BAM_DMUX_NUM_SKB; i++) {
                if (!bam_dmux_skb_dma_queue_rx(&dmux->rx_skbs[i], GFP_KERNEL))
                        return false;
        }
        dma_async_issue_pending(dmux->rx);

        return true;
}

static void bam_dmux_free_skbs(struct bam_dmux_skb_dma skbs[],
                               enum dma_data_direction dir)
{
        int i;

        for (i = 0; i < BAM_DMUX_NUM_SKB; i++) {
                struct bam_dmux_skb_dma *skb_dma = &skbs[i];

                if (skb_dma->addr)
                        bam_dmux_skb_dma_unmap(skb_dma, dir);
                if (skb_dma->skb) {
                        dev_kfree_skb(skb_dma->skb);
                        skb_dma->skb = NULL;
                }
        }
}

static void bam_dmux_power_off(struct bam_dmux *dmux)
{
        if (dmux->tx) {
                dmaengine_terminate_sync(dmux->tx);
                dma_release_channel(dmux->tx);
                dmux->tx = NULL;
        }

        if (dmux->rx) {
                dmaengine_terminate_sync(dmux->rx);
                dma_release_channel(dmux->rx);
                dmux->rx = NULL;
        }

        bam_dmux_free_skbs(dmux->rx_skbs, DMA_FROM_DEVICE);
}

static irqreturn_t bam_dmux_pc_irq(int irq, void *data)
{
        struct bam_dmux *dmux = data;
        bool new_state = !dmux->pc_state;

        dev_dbg(dmux->dev, "pc: %u\n", new_state);

        if (new_state) {
                if (bam_dmux_power_on(dmux))
                        bam_dmux_pc_ack(dmux);
                else
                        bam_dmux_power_off(dmux);
        } else {
                bam_dmux_power_off(dmux);
                bam_dmux_pc_ack(dmux);
        }

        dmux->pc_state = new_state;
        wake_up_all(&dmux->pc_wait);

        return IRQ_HANDLED;
}

static irqreturn_t bam_dmux_pc_ack_irq(int irq, void *data)
{
        struct bam_dmux *dmux = data;

        dev_dbg(dmux->dev, "pc ack\n");
        complete_all(&dmux->pc_ack_completion);

        return IRQ_HANDLED;
}

static int bam_dmux_runtime_suspend(struct device *dev)
{
        struct bam_dmux *dmux = dev_get_drvdata(dev);

        dev_dbg(dev, "runtime suspend\n");
        bam_dmux_pc_vote(dmux, false);

        return 0;
}

static int __maybe_unused bam_dmux_runtime_resume(struct device *dev)
{
        struct bam_dmux *dmux = dev_get_drvdata(dev);

        dev_dbg(dev, "runtime resume\n");

        /* Wait until previous power down was acked */
        if (!wait_for_completion_timeout(&dmux->pc_ack_completion,
                                         BAM_DMUX_REMOTE_TIMEOUT))
                return -ETIMEDOUT;

        /* Vote for power state */
        bam_dmux_pc_vote(dmux, true);

        /* Wait for ack */
        if (!wait_for_completion_timeout(&dmux->pc_ack_completion,
                                         BAM_DMUX_REMOTE_TIMEOUT)) {
                bam_dmux_pc_vote(dmux, false);
                return -ETIMEDOUT;
        }

        /* Wait until we're up */
        if (!wait_event_timeout(dmux->pc_wait, dmux->pc_state,
                                BAM_DMUX_REMOTE_TIMEOUT)) {
                bam_dmux_pc_vote(dmux, false);
                return -ETIMEDOUT;
        }

        /* Ensure that we actually initialized successfully */
        if (!dmux->rx) {
                bam_dmux_pc_vote(dmux, false);
                return -ENXIO;
        }

        /* Request TX channel if necessary */
        if (dmux->tx)
                return 0;

        dmux->tx = dma_request_chan(dev, "tx");
        if (IS_ERR(dmux->tx)) {
                dev_err(dev, "Failed to request TX DMA channel: %pe\n", dmux->tx);
                dmux->tx = NULL;
                bam_dmux_runtime_suspend(dev);
                return -ENXIO;
        }

        return 0;
}

static int bam_dmux_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct bam_dmux *dmux;
        int ret, pc_ack_irq, i;
        unsigned int bit;

        dmux = devm_kzalloc(dev, sizeof(*dmux), GFP_KERNEL);
        if (!dmux)
                return -ENOMEM;

        dmux->dev = dev;
        platform_set_drvdata(pdev, dmux);

        dmux->pc_irq = platform_get_irq_byname(pdev, "pc");
        if (dmux->pc_irq < 0)
                return dmux->pc_irq;

        pc_ack_irq = platform_get_irq_byname(pdev, "pc-ack");
        if (pc_ack_irq < 0)
                return pc_ack_irq;

        dmux->pc = devm_qcom_smem_state_get(dev, "pc", &bit);
        if (IS_ERR(dmux->pc))
                return dev_err_probe(dev, PTR_ERR(dmux->pc),
                                     "Failed to get pc state\n");
        dmux->pc_mask = BIT(bit);

        dmux->pc_ack = devm_qcom_smem_state_get(dev, "pc-ack", &bit);
        if (IS_ERR(dmux->pc_ack))
                return dev_err_probe(dev, PTR_ERR(dmux->pc_ack),
                                     "Failed to get pc-ack state\n");
        dmux->pc_ack_mask = BIT(bit);

        init_waitqueue_head(&dmux->pc_wait);
        init_completion(&dmux->pc_ack_completion);
        complete_all(&dmux->pc_ack_completion);

        spin_lock_init(&dmux->tx_lock);
        INIT_WORK(&dmux->tx_wakeup_work, bam_dmux_tx_wakeup_work);
        INIT_WORK(&dmux->register_netdev_work, bam_dmux_register_netdev_work);

        for (i = 0; i < BAM_DMUX_NUM_SKB; i++) {
                dmux->rx_skbs[i].dmux = dmux;
                dmux->tx_skbs[i].dmux = dmux;
        }

        /* Runtime PM manages our own power vote.
         * Note that the RX path may be active even if we are runtime suspended,
         * since it is controlled by the remote side.
         */
        pm_runtime_set_autosuspend_delay(dev, BAM_DMUX_AUTOSUSPEND_DELAY);
        pm_runtime_use_autosuspend(dev);
        pm_runtime_enable(dev);

        ret = devm_request_threaded_irq(dev, pc_ack_irq, NULL, bam_dmux_pc_ack_irq,
                                        IRQF_ONESHOT, NULL, dmux);
        if (ret)
                goto err_disable_pm;

        ret = devm_request_threaded_irq(dev, dmux->pc_irq, NULL, bam_dmux_pc_irq,
                                        IRQF_ONESHOT, NULL, dmux);
        if (ret)
                goto err_disable_pm;

        ret = irq_get_irqchip_state(dmux->pc_irq, IRQCHIP_STATE_LINE_LEVEL,
                                    &dmux->pc_state);
        if (ret)
                goto err_disable_pm;

        /* Check if remote finished initialization before us */
        if (dmux->pc_state) {
                if (bam_dmux_power_on(dmux))
                        bam_dmux_pc_ack(dmux);
                else
                        bam_dmux_power_off(dmux);
        }

        return 0;

err_disable_pm:
        pm_runtime_disable(dev);
        pm_runtime_dont_use_autosuspend(dev);
        return ret;
}

static void bam_dmux_remove(struct platform_device *pdev)
{
        struct bam_dmux *dmux = platform_get_drvdata(pdev);
        struct device *dev = dmux->dev;
        LIST_HEAD(list);
        int i;

        /* Unregister network interfaces */
        cancel_work_sync(&dmux->register_netdev_work);
        rtnl_lock();
        for (i = 0; i < BAM_DMUX_NUM_CH; ++i)
                if (dmux->netdevs[i])
                        unregister_netdevice_queue(dmux->netdevs[i], &list);
        unregister_netdevice_many(&list);
        rtnl_unlock();
        cancel_work_sync(&dmux->tx_wakeup_work);

        /* Drop our own power vote */
        pm_runtime_disable(dev);
        pm_runtime_dont_use_autosuspend(dev);
        bam_dmux_runtime_suspend(dev);
        pm_runtime_set_suspended(dev);

        /* Try to wait for remote side to drop power vote */
        if (!wait_event_timeout(dmux->pc_wait, !dmux->rx, BAM_DMUX_REMOTE_TIMEOUT))
                dev_err(dev, "Timed out waiting for remote side to suspend\n");

        /* Make sure everything is cleaned up before we return */
        disable_irq(dmux->pc_irq);
        bam_dmux_power_off(dmux);
        bam_dmux_free_skbs(dmux->tx_skbs, DMA_TO_DEVICE);
}

static const struct dev_pm_ops bam_dmux_pm_ops = {
        SET_RUNTIME_PM_OPS(bam_dmux_runtime_suspend, bam_dmux_runtime_resume, NULL)
};

static const struct of_device_id bam_dmux_of_match[] = {
        { .compatible = "qcom,bam-dmux" },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, bam_dmux_of_match);

static struct platform_driver bam_dmux_driver = {
        .probe = bam_dmux_probe,
        .remove = bam_dmux_remove,
        .driver = {
                .name = "bam-dmux",
                .pm = &bam_dmux_pm_ops,
                .of_match_table = bam_dmux_of_match,
        },
};
module_platform_driver(bam_dmux_driver);

MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Qualcomm BAM-DMUX WWAN Network Driver");
MODULE_AUTHOR("Stephan Gerhold <stephan@gerhold.net>");