// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Driver for Broadcom BCM2835 auxiliary SPI Controllers
 *
 * the driver does not rely on the native chipselects at all
 * but only uses the gpio type chipselects
 *
 * Based on: spi-bcm2835.c
 *
 * Copyright (C) 2015 Martin Sperl
 */

#include <linux/clk.h>
#include <linux/completion.h>
#include <linux/debugfs.h>
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/regmap.h>
#include <linux/spi/spi.h>
#include <linux/spinlock.h>

/* define polling limits */
static unsigned int polling_limit_us = 30;
module_param(polling_limit_us, uint, 0664);
MODULE_PARM_DESC(polling_limit_us,
                 "time in us to run a transfer in polling mode - if zero no polling is used\n");

/*
 * spi register defines
 *
 * note there is garbage in the "official" documentation,
 * so some data is taken from the file:
 *   brcm_usrlib/dag/vmcsx/vcinclude/bcm2708_chip/aux_io.h
 * inside of:
 *   http://www.broadcom.com/docs/support/videocore/Brcm_Android_ICS_Graphics_Stack.tar.gz
 */

/* SPI register offsets */
#define BCM2835_AUX_SPI_CNTL0   0x00
#define BCM2835_AUX_SPI_CNTL1   0x04
#define BCM2835_AUX_SPI_STAT    0x08
#define BCM2835_AUX_SPI_PEEK    0x0C
#define BCM2835_AUX_SPI_IO      0x20
#define BCM2835_AUX_SPI_TXHOLD  0x30

/* Bitfields in CNTL0 */
#define BCM2835_AUX_SPI_CNTL0_SPEED     0xFFF00000
#define BCM2835_AUX_SPI_CNTL0_SPEED_MAX 0xFFF
#define BCM2835_AUX_SPI_CNTL0_SPEED_SHIFT       20
#define BCM2835_AUX_SPI_CNTL0_CS        0x000E0000
#define BCM2835_AUX_SPI_CNTL0_POSTINPUT 0x00010000
#define BCM2835_AUX_SPI_CNTL0_VAR_CS    0x00008000
#define BCM2835_AUX_SPI_CNTL0_VAR_WIDTH 0x00004000
#define BCM2835_AUX_SPI_CNTL0_DOUTHOLD  0x00003000
#define BCM2835_AUX_SPI_CNTL0_ENABLE    0x00000800
#define BCM2835_AUX_SPI_CNTL0_IN_RISING 0x00000400
#define BCM2835_AUX_SPI_CNTL0_CLEARFIFO 0x00000200
#define BCM2835_AUX_SPI_CNTL0_OUT_RISING        0x00000100
#define BCM2835_AUX_SPI_CNTL0_CPOL      0x00000080
#define BCM2835_AUX_SPI_CNTL0_MSBF_OUT  0x00000040
#define BCM2835_AUX_SPI_CNTL0_SHIFTLEN  0x0000003F

/* Bitfields in CNTL1 */
#define BCM2835_AUX_SPI_CNTL1_CSHIGH    0x00000700
#define BCM2835_AUX_SPI_CNTL1_TXEMPTY   0x00000080
#define BCM2835_AUX_SPI_CNTL1_IDLE      0x00000040
#define BCM2835_AUX_SPI_CNTL1_MSBF_IN   0x00000002
#define BCM2835_AUX_SPI_CNTL1_KEEP_IN   0x00000001

/* Bitfields in STAT */
#define BCM2835_AUX_SPI_STAT_TX_LVL     0xFF000000
#define BCM2835_AUX_SPI_STAT_RX_LVL     0x00FF0000
#define BCM2835_AUX_SPI_STAT_TX_FULL    0x00000400
#define BCM2835_AUX_SPI_STAT_TX_EMPTY   0x00000200
#define BCM2835_AUX_SPI_STAT_RX_FULL    0x00000100
#define BCM2835_AUX_SPI_STAT_RX_EMPTY   0x00000080
#define BCM2835_AUX_SPI_STAT_BUSY       0x00000040
#define BCM2835_AUX_SPI_STAT_BITCOUNT   0x0000003F

struct bcm2835aux_spi {
        void __iomem *regs;
        struct clk *clk;
        int irq;
        u32 cntl[2];
        const u8 *tx_buf;
        u8 *rx_buf;
        int tx_len;
        int rx_len;
        int pending;

        u64 count_transfer_polling;
        u64 count_transfer_irq;
        u64 count_transfer_irq_after_poll;

        struct dentry *debugfs_dir;
};

#if defined(CONFIG_DEBUG_FS)
static void bcm2835aux_debugfs_create(struct bcm2835aux_spi *bs,
                                      const char *dname)
{
        char name[64];
        struct dentry *dir;

        /* get full name */
        snprintf(name, sizeof(name), "spi-bcm2835aux-%s", dname);

        /* the base directory */
        dir = debugfs_create_dir(name, NULL);
        bs->debugfs_dir = dir;

        /* the counters */
        debugfs_create_u64("count_transfer_polling", 0444, dir,
                           &bs->count_transfer_polling);
        debugfs_create_u64("count_transfer_irq", 0444, dir,
                           &bs->count_transfer_irq);
        debugfs_create_u64("count_transfer_irq_after_poll", 0444, dir,
                           &bs->count_transfer_irq_after_poll);
}

static void bcm2835aux_debugfs_remove(struct bcm2835aux_spi *bs)
{
        debugfs_remove_recursive(bs->debugfs_dir);
        bs->debugfs_dir = NULL;
}
#else
static void bcm2835aux_debugfs_create(struct bcm2835aux_spi *bs,
                                      const char *dname)
{
}

static void bcm2835aux_debugfs_remove(struct bcm2835aux_spi *bs)
{
}
#endif /* CONFIG_DEBUG_FS */

static inline u32 bcm2835aux_rd(struct bcm2835aux_spi *bs, unsigned int reg)
{
        return readl(bs->regs + reg);
}

static inline void bcm2835aux_wr(struct bcm2835aux_spi *bs, unsigned int reg,
                                 u32 val)
{
        writel(val, bs->regs + reg);
}

static inline void bcm2835aux_rd_fifo(struct bcm2835aux_spi *bs)
{
        u32 data;
        int count = min(bs->rx_len, 3);

        data = bcm2835aux_rd(bs, BCM2835_AUX_SPI_IO);
        if (bs->rx_buf) {
                switch (count) {
                case 3:
                        *bs->rx_buf++ = (data >> 16) & 0xff;
                        fallthrough;
                case 2:
                        *bs->rx_buf++ = (data >> 8) & 0xff;
                        fallthrough;
                case 1:
                        *bs->rx_buf++ = (data >> 0) & 0xff;
                        /* fallthrough - no default */
                }
        }
        bs->rx_len -= count;
        bs->pending -= count;
}

static inline void bcm2835aux_wr_fifo(struct bcm2835aux_spi *bs)
{
        u32 data;
        u8 byte;
        int count;
        int i;

        /* gather up to 3 bytes to write to the FIFO */
        count = min(bs->tx_len, 3);
        data = 0;
        for (i = 0; i < count; i++) {
                byte = bs->tx_buf ? *bs->tx_buf++ : 0;
                data |= byte << (8 * (2 - i));
        }

        /* and set the variable bit-length */
        data |= (count * 8) << 24;

        /* and decrement length */
        bs->tx_len -= count;
        bs->pending += count;

        /* write to the correct TX-register */
        if (bs->tx_len)
                bcm2835aux_wr(bs, BCM2835_AUX_SPI_TXHOLD, data);
        else
                bcm2835aux_wr(bs, BCM2835_AUX_SPI_IO, data);
}

static void bcm2835aux_spi_reset_hw(struct bcm2835aux_spi *bs)
{
        /* disable spi clearing fifo and interrupts */
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, 0);
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL0,
                      BCM2835_AUX_SPI_CNTL0_CLEARFIFO);
}

static void bcm2835aux_spi_transfer_helper(struct bcm2835aux_spi *bs)
{
        u32 stat = bcm2835aux_rd(bs, BCM2835_AUX_SPI_STAT);

        /* check if we have data to read */
        for (; bs->rx_len && (stat & BCM2835_AUX_SPI_STAT_RX_LVL);
             stat = bcm2835aux_rd(bs, BCM2835_AUX_SPI_STAT))
                bcm2835aux_rd_fifo(bs);

        /* check if we have data to write */
        while (bs->tx_len &&
               (bs->pending < 12) &&
               (!(bcm2835aux_rd(bs, BCM2835_AUX_SPI_STAT) &
                  BCM2835_AUX_SPI_STAT_TX_FULL))) {
                bcm2835aux_wr_fifo(bs);
        }
}

static irqreturn_t bcm2835aux_spi_interrupt(int irq, void *dev_id)
{
        struct spi_controller *host = dev_id;
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);

        /* IRQ may be shared, so return if our interrupts are disabled */
        if (!(bcm2835aux_rd(bs, BCM2835_AUX_SPI_CNTL1) &
              (BCM2835_AUX_SPI_CNTL1_TXEMPTY | BCM2835_AUX_SPI_CNTL1_IDLE)))
                return IRQ_NONE;

        /* do common fifo handling */
        bcm2835aux_spi_transfer_helper(bs);

        if (!bs->tx_len) {
                /* disable tx fifo empty interrupt */
                bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, bs->cntl[1] |
                        BCM2835_AUX_SPI_CNTL1_IDLE);
        }

        /* and if rx_len is 0 then disable interrupts and wake up completion */
        if (!bs->rx_len) {
                bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, bs->cntl[1]);
                spi_finalize_current_transfer(host);
        }

        return IRQ_HANDLED;
}

static int __bcm2835aux_spi_transfer_one_irq(struct spi_controller *host,
                                             struct spi_device *spi,
                                             struct spi_transfer *tfr)
{
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);

        /* enable interrupts */
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, bs->cntl[1] |
                BCM2835_AUX_SPI_CNTL1_TXEMPTY |
                BCM2835_AUX_SPI_CNTL1_IDLE);

        /* and wait for finish... */
        return 1;
}

static int bcm2835aux_spi_transfer_one_irq(struct spi_controller *host,
                                           struct spi_device *spi,
                                           struct spi_transfer *tfr)
{
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);

        /* update statistics */
        bs->count_transfer_irq++;

        /* fill in registers and fifos before enabling interrupts */
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, bs->cntl[1]);
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL0, bs->cntl[0]);

        /* fill in tx fifo with data before enabling interrupts */
        while ((bs->tx_len) &&
               (bs->pending < 12) &&
               (!(bcm2835aux_rd(bs, BCM2835_AUX_SPI_STAT) &
                  BCM2835_AUX_SPI_STAT_TX_FULL))) {
                bcm2835aux_wr_fifo(bs);
        }

        /* now run the interrupt mode */
        return __bcm2835aux_spi_transfer_one_irq(host, spi, tfr);
}

static int bcm2835aux_spi_transfer_one_poll(struct spi_controller *host,
                                            struct spi_device *spi,
                                        struct spi_transfer *tfr)
{
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);
        unsigned long timeout;

        /* update statistics */
        bs->count_transfer_polling++;

        /* configure spi */
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, bs->cntl[1]);
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL0, bs->cntl[0]);

        /* set the timeout to at least 2 jiffies */
        timeout = jiffies + 2 + HZ * polling_limit_us / 1000000;

        /* loop until finished the transfer */
        while (bs->rx_len) {

                /* do common fifo handling */
                bcm2835aux_spi_transfer_helper(bs);

                /* there is still data pending to read check the timeout */
                if (bs->rx_len && time_after(jiffies, timeout)) {
                        dev_dbg_ratelimited(&spi->dev,
                                            "timeout period reached: jiffies: %lu remaining tx/rx: %d/%d - falling back to interrupt mode\n",
                                            jiffies - timeout,
                                            bs->tx_len, bs->rx_len);
                        /* forward to interrupt handler */
                        bs->count_transfer_irq_after_poll++;
                        return __bcm2835aux_spi_transfer_one_irq(host,
                                                               spi, tfr);
                }
        }

        /* and return without waiting for completion */
        return 0;
}

static int bcm2835aux_spi_transfer_one(struct spi_controller *host,
                                       struct spi_device *spi,
                                       struct spi_transfer *tfr)
{
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);
        unsigned long spi_hz, clk_hz, speed;
        unsigned long hz_per_byte, byte_limit;

        /* calculate the registers to handle
         *
         * note that we use the variable data mode, which
         * is not optimal for longer transfers as we waste registers
         * resulting (potentially) in more interrupts when transferring
         * more than 12 bytes
         */

        /* set clock */
        spi_hz = tfr->speed_hz;
        clk_hz = clk_get_rate(bs->clk);

        if (spi_hz >= clk_hz / 2) {
                speed = 0;
        } else if (spi_hz) {
                speed = DIV_ROUND_UP(clk_hz, 2 * spi_hz) - 1;
                if (speed >  BCM2835_AUX_SPI_CNTL0_SPEED_MAX)
                        speed = BCM2835_AUX_SPI_CNTL0_SPEED_MAX;
        } else { /* the slowest we can go */
                speed = BCM2835_AUX_SPI_CNTL0_SPEED_MAX;
        }
        /* mask out old speed from previous spi_transfer */
        bs->cntl[0] &= ~(BCM2835_AUX_SPI_CNTL0_SPEED);
        /* set the new speed */
        bs->cntl[0] |= speed << BCM2835_AUX_SPI_CNTL0_SPEED_SHIFT;

        tfr->effective_speed_hz = clk_hz / (2 * (speed + 1));

        /* set transmit buffers and length */
        bs->tx_buf = tfr->tx_buf;
        bs->rx_buf = tfr->rx_buf;
        bs->tx_len = tfr->len;
        bs->rx_len = tfr->len;
        bs->pending = 0;

        /* Calculate the estimated time in us the transfer runs.  Note that
         * there are 2 idle clocks cycles after each chunk getting
         * transferred - in our case the chunk size is 3 bytes, so we
         * approximate this by 9 cycles/byte.  This is used to find the number
         * of Hz per byte per polling limit.  E.g., we can transfer 1 byte in
         * 30 µs per 300,000 Hz of bus clock.
         */
        hz_per_byte = polling_limit_us ? (9 * 1000000) / polling_limit_us : 0;
        byte_limit = hz_per_byte ? tfr->effective_speed_hz / hz_per_byte : 1;

        /* run in polling mode for short transfers */
        if (tfr->len < byte_limit)
                return bcm2835aux_spi_transfer_one_poll(host, spi, tfr);

        /* run in interrupt mode for all others */
        return bcm2835aux_spi_transfer_one_irq(host, spi, tfr);
}

static int bcm2835aux_spi_prepare_message(struct spi_controller *host,
                                          struct spi_message *msg)
{
        struct spi_device *spi = msg->spi;
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);

        bs->cntl[0] = BCM2835_AUX_SPI_CNTL0_ENABLE |
                      BCM2835_AUX_SPI_CNTL0_VAR_WIDTH |
                      BCM2835_AUX_SPI_CNTL0_MSBF_OUT;
        bs->cntl[1] = BCM2835_AUX_SPI_CNTL1_MSBF_IN;

        /* handle all the modes */
        if (spi->mode & SPI_CPOL) {
                bs->cntl[0] |= BCM2835_AUX_SPI_CNTL0_CPOL;
                bs->cntl[0] |= BCM2835_AUX_SPI_CNTL0_OUT_RISING;
        } else {
                bs->cntl[0] |= BCM2835_AUX_SPI_CNTL0_IN_RISING;
        }
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, bs->cntl[1]);
        bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL0, bs->cntl[0]);

        return 0;
}

static int bcm2835aux_spi_unprepare_message(struct spi_controller *host,
                                            struct spi_message *msg)
{
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);

        bcm2835aux_spi_reset_hw(bs);

        return 0;
}

static void bcm2835aux_spi_handle_err(struct spi_controller *host,
                                      struct spi_message *msg)
{
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);

        bcm2835aux_spi_reset_hw(bs);
}

static int bcm2835aux_spi_setup(struct spi_device *spi)
{
        /* sanity check for native cs */
        if (spi->mode & SPI_NO_CS)
                return 0;

        if (spi_get_csgpiod(spi, 0))
                return 0;

        /* for dt-backwards compatibility: only support native on CS0
         * known things not supported with broken native CS:
         * * multiple chip-selects: cs0-cs2 are all
         *     simultaniously asserted whenever there is a transfer
         *     this even includes SPI_NO_CS
         * * SPI_CS_HIGH: cs are always asserted low
         * * cs_change: cs is deasserted after each spi_transfer
         * * cs_delay_usec: cs is always deasserted one SCK cycle
         *     after the last transfer
         * probably more...
         */
        dev_warn(&spi->dev,
                 "Native CS is not supported - please configure cs-gpio in device-tree\n");

        if (spi_get_chipselect(spi, 0) == 0)
                return 0;

        dev_warn(&spi->dev, "Native CS is not working for cs > 0\n");

        return -EINVAL;
}

static int bcm2835aux_spi_probe(struct platform_device *pdev)
{
        struct spi_controller *host;
        struct bcm2835aux_spi *bs;
        unsigned long clk_hz;
        int err;

        host = devm_spi_alloc_host(&pdev->dev, sizeof(*bs));
        if (!host)
                return -ENOMEM;

        platform_set_drvdata(pdev, host);
        host->mode_bits = (SPI_CPOL | SPI_CS_HIGH | SPI_NO_CS);
        host->bits_per_word_mask = SPI_BPW_MASK(8);
        /* even though the driver never officially supported native CS
         * allow a single native CS for legacy DT support purposes when
         * no cs-gpio is configured.
         * Known limitations for native cs are:
         * * multiple chip-selects: cs0-cs2 are all simultaniously asserted
         *     whenever there is a transfer -  this even includes SPI_NO_CS
         * * SPI_CS_HIGH: is ignores - cs are always asserted low
         * * cs_change: cs is deasserted after each spi_transfer
         * * cs_delay_usec: cs is always deasserted one SCK cycle after
         *     a spi_transfer
         */
        host->num_chipselect = 1;
        host->setup = bcm2835aux_spi_setup;
        host->transfer_one = bcm2835aux_spi_transfer_one;
        host->handle_err = bcm2835aux_spi_handle_err;
        host->prepare_message = bcm2835aux_spi_prepare_message;
        host->unprepare_message = bcm2835aux_spi_unprepare_message;
        host->use_gpio_descriptors = true;

        bs = spi_controller_get_devdata(host);

        /* the main area */
        bs->regs = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(bs->regs))
                return PTR_ERR(bs->regs);

        bs->clk = devm_clk_get_enabled(&pdev->dev, NULL);
        if (IS_ERR(bs->clk)) {
                err = PTR_ERR(bs->clk);
                dev_err(&pdev->dev, "could not get clk: %d\n", err);
                return err;
        }

        bs->irq = platform_get_irq(pdev, 0);
        if (bs->irq < 0)
                return bs->irq;

        /* just checking if the clock returns a sane value */
        clk_hz = clk_get_rate(bs->clk);
        if (!clk_hz) {
                dev_err(&pdev->dev, "clock returns 0 Hz\n");
                return -ENODEV;
        }

        /* reset SPI-HW block */
        bcm2835aux_spi_reset_hw(bs);

        err = devm_request_irq(&pdev->dev, bs->irq,
                               bcm2835aux_spi_interrupt,
                               IRQF_SHARED,
                               dev_name(&pdev->dev), host);
        if (err) {
                dev_err(&pdev->dev, "could not request IRQ: %d\n", err);
                return err;
        }

        err = spi_register_controller(host);
        if (err) {
                dev_err(&pdev->dev, "could not register SPI host: %d\n", err);
                return err;
        }

        bcm2835aux_debugfs_create(bs, dev_name(&pdev->dev));

        return 0;
}

static void bcm2835aux_spi_remove(struct platform_device *pdev)
{
        struct spi_controller *host = platform_get_drvdata(pdev);
        struct bcm2835aux_spi *bs = spi_controller_get_devdata(host);

        bcm2835aux_debugfs_remove(bs);

        spi_unregister_controller(host);

        bcm2835aux_spi_reset_hw(bs);
}

static const struct of_device_id bcm2835aux_spi_match[] = {
        { .compatible = "brcm,bcm2835-aux-spi", },
        {}
};
MODULE_DEVICE_TABLE(of, bcm2835aux_spi_match);

static struct platform_driver bcm2835aux_spi_driver = {
        .driver         = {
                .name           = "spi-bcm2835aux",
                .of_match_table = bcm2835aux_spi_match,
        },
        .probe          = bcm2835aux_spi_probe,
        .remove         = bcm2835aux_spi_remove,
};
module_platform_driver(bcm2835aux_spi_driver);

MODULE_DESCRIPTION("SPI controller driver for Broadcom BCM2835 aux");
MODULE_AUTHOR("Martin Sperl <kernel@martin.sperl.org>");
MODULE_LICENSE("GPL");