Re: [PATCH v2 10/14] spi: bcm63xx-hsspi: Add prepend mode support

From: Jonas Gorski
Date: Thu Jan 26 2023 - 10:15:19 EST

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In reply to: William Zhang: "[PATCH v2 10/14] spi: bcm63xx-hsspi: Add prepend mode support"
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On Tue, 24 Jan 2023 at 23:33, William Zhang <william.zhang@xxxxxxxxxxxx> wrote:
>
> Due to the controller limitation to keep the chip select low during the
> bus idle time between the transfer, a dummy cs workaround was used when
> this driver was first upstreamed to the kernel. It basically picks the
> dummy cs as !actual_cs so typically dummy cs is 1 when most of the case
> only cs 0 is used in the board design. Then invert the polarity of both
> cs and tell the controller to start the transfers using dummy cs.
> Assuming both cs are active low before the inversion, effectively this
> keeps dummy cs high and actual cs low during the transfer and workaround
> the issue.
>
> This workaround implies that dummy cs 1 pin has to be set to chip
> selection function in the pinmux when the transfer clock is above
> 25MHz. The old chips likely have default pinmux set to chip select on
> the dummy cs pin so it works but this is not case for the new Broadband
> BCA chips and this workaround stop working. This is specifically an
> issue to support SPI NAND and SPI NOR flash because these flash devices
> can typically run at or above 100MHz.
>
> This patch utilizes the prepend feature of the controller to combine the
> multiple transfers in the same message to a single transfer when
> possible. This way there is no need to keep clock low between transfers
> and solve the issue without any hardware requirement.
>
> Multiple transfers within a SPI message may be combined into one
> transfer if the following are all true:
> * One or more half duplex write transfer in single bit mode
> * Optional full duplex read/write at the end
> * No delay and cs_change between transfers
>
> Most of the SPI device meets this requirements such as SPI NOR,
> SPI NAND flash, Broadcom SPI voice card and etc. For any SPI message
> that does not meet the above requirement to combine the transfers, we
> switch to original dummy cs mode but limit the clock rate to the safe
> 25MHz. This is the default auto transfer mode and it makes sure all the
> SPI message can be supported automatically under the hood.
>
> This patch also adds the driver sysfs node xfer_mode to provide
> the option for overriding the default auto mode and force it to dummy cs
> or prepend mode.
>
> Signed-off-by: William Zhang <william.zhang@xxxxxxxxxxxx>
>
> ---
>
> Changes in v2:
> - Fix build error for Alpha platform
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> - Remove use_cs_workaround option from device tree
> - Change the transfer logic to use try prepend first and if not
> prependable, switch to dummy cs mode with clock limit at the 25MHz
> - Add driver sysfs node xfer_mode for the option to override the
> transfer mode to dummy cs or prepend mode.
> - Add number of bits check in the tranfer for prepend mode eligibility
> check
> - Update commit message
>
> drivers/spi/spi-bcm63xx-hsspi.c | 332 +++++++++++++++++++++++++++++---
> 1 file changed, 300 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/spi/spi-bcm63xx-hsspi.c b/drivers/spi/spi-bcm63xx-hsspi.c
> index 8f0d31764f98..2a0bef943967 100644
> --- a/drivers/spi/spi-bcm63xx-hsspi.c
> +++ b/drivers/spi/spi-bcm63xx-hsspi.c
> @@ -93,7 +93,11 @@
>
> #define HSSPI_MAX_PREPEND_LEN 15
>
> -#define HSSPI_MAX_SYNC_CLOCK 30000000
> +/*
> + * Some chip require 30MHz but other require 25MHz. Use smaller value to cover
> + * both cases.
> + */
> +#define HSSPI_MAX_SYNC_CLOCK 25000000
>
> #define HSSPI_SPI_MAX_CS 8
> #define HSSPI_BUS_NUM 1 /* 0 is legacy SPI */
> @@ -103,6 +107,16 @@
> #define HSSPI_WAIT_MODE_INTR 1
> #define HSSPI_WAIT_MODE_MAX HSSPI_WAIT_MODE_INTR
>
> +/*
> + * Default transfer mode is auto. If the msg is prependable, use the prepend
> + * mode. If not, falls back to use the dummy cs workaround mode but limit the
> + * clock to 25MHz to make sure it works in all board design.
> + */
> +#define HSSPI_XFER_MODE_AUTO 0
> +#define HSSPI_XFER_MODE_PREPEND 1
> +#define HSSPI_XFER_MODE_DUMMYCS 2
> +#define HSSPI_XFER_MODE_MAX HSSPI_XFER_MODE_DUMMYCS
> +
> struct bcm63xx_hsspi {
> struct completion done;
> struct mutex bus_mutex;
> @@ -116,6 +130,9 @@ struct bcm63xx_hsspi {
> u32 speed_hz;
> u8 cs_polarity;
> u32 wait_mode;
> + u32 xfer_mode;
> + u32 prepend_cnt;
> + u8 *prepend_buf;
> };
>
> static ssize_t wait_mode_show(struct device *dev, struct device_attribute *attr,
> @@ -154,8 +171,42 @@ static ssize_t wait_mode_store(struct device *dev, struct device_attribute *attr
>
> static DEVICE_ATTR_RW(wait_mode);
>
> +static ssize_t xfer_mode_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + struct spi_controller *ctrl = dev_get_drvdata(dev);
> + struct bcm63xx_hsspi *bs = spi_master_get_devdata(ctrl);
> +
> + return sprintf(buf, "%d\n", bs->xfer_mode);
> +}
> +
> +static ssize_t xfer_mode_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct spi_controller *ctrl = dev_get_drvdata(dev);
> + struct bcm63xx_hsspi *bs = spi_master_get_devdata(ctrl);
> + u32 val;
> +
> + if (kstrtou32(buf, 10, &val))
> + return -EINVAL;
> +
> + if (val > HSSPI_XFER_MODE_MAX) {
> + dev_warn(dev, "invalid xfer mode %u\n", val);
> + return -EINVAL;
> + }
> +
> + mutex_lock(&bs->msg_mutex);
> + bs->xfer_mode = val;
> + mutex_unlock(&bs->msg_mutex);
> +
> + return count;
> +}
> +
> +static DEVICE_ATTR_RW(xfer_mode);
> +
> static struct attribute *bcm63xx_hsspi_attrs[] = {
> &dev_attr_wait_mode.attr,
> + &dev_attr_xfer_mode.attr,
> NULL,
> };
>
> @@ -163,6 +214,208 @@ static const struct attribute_group bcm63xx_hsspi_group = {
> .attrs = bcm63xx_hsspi_attrs,
> };
>
> +static void bcm63xx_hsspi_set_clk(struct bcm63xx_hsspi *bs,
> + struct spi_device *spi, int hz);
> +
> +static size_t bcm63xx_hsspi_max_message_size(struct spi_device *spi)
> +{
> + return HSSPI_BUFFER_LEN - HSSPI_OPCODE_LEN;
> +}
> +
> +static int bcm63xx_hsspi_wait_cmd(struct bcm63xx_hsspi *bs)
> +{
> + unsigned long limit;
> + u32 reg = 0;
> + int rc = 0;

If the only possible return values are 0 and 1, maybe this should be a bool?

> +
> + if (bs->wait_mode == HSSPI_WAIT_MODE_INTR) {
> + if (wait_for_completion_timeout(&bs->done, HZ) == 0)
> + rc = 1;
> + } else {
> + /* polling mode checks for status busy bit */
> + limit = jiffies + msecs_to_jiffies(HSSPI_POLL_STATUS_TIMEOUT_MS);
> +
> + while (!time_after(jiffies, limit)) {
> + reg = __raw_readl(bs->regs + HSSPI_PINGPONG_STATUS_REG(0));
> + if (reg & HSSPI_PINGPONG_STATUS_SRC_BUSY)
> + cpu_relax();
> + else
> + break;
> + }
> + if (reg & HSSPI_PINGPONG_STATUS_SRC_BUSY)
> + rc = 1;
> + }
> +
> + if (rc)
> + dev_err(&bs->pdev->dev, "transfer timed out!\n");
> +
> + return rc;
> +}
> +
> +static bool bcm63xx_check_msg_prependable(struct spi_master *master,
> + struct spi_message *msg,
> + struct spi_transfer *t_prepend)

This function does more than just checking, so I think a more
appropriate name would be something like

bcm63xx_prepare_prepend_transfer()

> +{
> +
> + struct bcm63xx_hsspi *bs = spi_master_get_devdata(master);
> + bool prepend = false, tx_only = false;
> + struct spi_transfer *t;
> +
> + /* If it is forced cs dummy workaround mode, no need to prepend message */
> + if (bs->xfer_mode == HSSPI_XFER_MODE_DUMMYCS)
> + return false;

That's a weird point for that, why not just move this to the caller
and check it before calling the function.

> +
> + /*
> + * Multiple transfers within a message may be combined into one transfer
> + * to the controller using its prepend feature. A SPI message is prependable
> + * only if the following are all true:
> + * 1. One or more half duplex write transfer in single bit mode
> + * 2. Optional full duplex read/write at the end
> + * 3. No delay and cs_change between transfers
> + */
> + bs->prepend_cnt = 0;
> + list_for_each_entry(t, &msg->transfers, transfer_list) {
> + if ((spi_delay_to_ns(&t->delay, t) > 0) || t->cs_change) {
> + dev_warn(&bs->pdev->dev,
> + "Delay or cs change not supported in prepend mode!\n");

I don't think warn is the right level. If we are on XFER_MODE_AUTO,
this should be _dbg, since we will just fall back to the dummy cs
mode, if we are on XFER_MODE_PREPEND, this should be dev_err, since we
cannot do the message.

cs->change is technically supported when all that's requested is a
between transfer cs toggle (t->cs_change is true, t->cs_off is false
and next transfer's cs_off is also false), which automatically happens
after the transfer. Not sure if it is worth the effort implementing
that though.

> + break;
> + }
> +
> + tx_only = false;
> + if (t->tx_buf && !t->rx_buf) {
> + tx_only = true;
> + if (bs->prepend_cnt + t->len >
> + (HSSPI_BUFFER_LEN - HSSPI_OPCODE_LEN)) {
> + dev_warn(&bs->pdev->dev,
> + "exceed max buf len, abort prepending transfers!\n");
> + break;

why not just return false here directly? And everywhere else where you
decided that you cannot use prepend.

> + }
> +
> + if (t->tx_nbits > SPI_NBITS_SINGLE &&
> + !list_is_last(&t->transfer_list, &msg->transfers)) {
> + dev_warn(&bs->pdev->dev,
> + "multi-bit prepend buf not supported!\n");
> + break;
> + }
> +
> + if (t->tx_nbits == SPI_NBITS_SINGLE) {
> + memcpy(bs->prepend_buf + bs->prepend_cnt, t->tx_buf, t->len);
> + bs->prepend_cnt += t->len;
> + }
> + } else {
> + if (!list_is_last(&t->transfer_list, &msg->transfers)) {
> + dev_warn(&bs->pdev->dev,
> + "rx/tx_rx transfer not supported when it is not last one!\n");

This is only an issue if doing multi-bit RX/TX; for single bit you can
just upgrade the whole transfer/message to duplex, you just need to
pick the read bytes then from the right offsets.

> + break;
> + }
> + }
> +
> + if (list_is_last(&t->transfer_list, &msg->transfers)) {
> + memcpy(t_prepend, t, sizeof(struct spi_transfer));
> +
> + if (tx_only && t->tx_nbits == SPI_NBITS_SINGLE) {
> + /*
> + * if the last one is also a single bit tx only transfer, merge
> + * all of them into one single tx transfer
> + */
> + t_prepend->len = bs->prepend_cnt;
> + t_prepend->tx_buf = bs->prepend_buf;
> + bs->prepend_cnt = 0;
> + } else {
> + /*
> + * if the last one is not a tx only transfer or dual tx xfer, all
> + * the previous transfers are sent through prepend bytes and
> + * make sure it does not exceed the max prepend len
> + */
> + if (bs->prepend_cnt > HSSPI_MAX_PREPEND_LEN) {
> + dev_warn(&bs->pdev->dev,
> + "exceed max prepend len, abort prepending transfers!\n");
> + break;

Likewise, you can merge any amount or rx/tx/rxtx single bit transfers
together as a duplex transfer with prepend len set to 0 (so
technically not a prepend anymore ;-)

> + }
> + }
> + prepend = true;
> + }
> + }
> +
> + return prepend;

and then if you already returned false if you cannot do prepend, you
just need to return true here and don't need the prepend variable.

> +}
> +
> +static int bcm63xx_hsspi_do_prepend_txrx(struct spi_device *spi,
> + struct spi_transfer *t)
> +{
> + struct bcm63xx_hsspi *bs = spi_master_get_devdata(spi->master);
> + unsigned int chip_select = spi->chip_select;
> + u16 opcode = 0;
> + const u8 *tx = t->tx_buf;
> + u8 *rx = t->rx_buf;
> + u32 reg = 0;
> +
> + /*
> + * shouldn't happen as we set the max_message_size in the probe.
> + * but check it again in case some driver does not honor the max size
> + */
> + if (t->len + bs->prepend_cnt > (HSSPI_BUFFER_LEN - HSSPI_OPCODE_LEN)) {
> + dev_warn(&bs->pdev->dev,
> + "Prepend message large than fifo size len %d prepend %d\n",
> + t->len, bs->prepend_cnt);
> + return -EINVAL;
> + }
> +
> + bcm63xx_hsspi_set_clk(bs, spi, t->speed_hz);
> +
> + if (tx && rx)
> + opcode = HSSPI_OP_READ_WRITE;
> + else if (tx)
> + opcode = HSSPI_OP_WRITE;
> + else if (rx)
> + opcode = HSSPI_OP_READ;
> +
> + if ((opcode == HSSPI_OP_READ && t->rx_nbits == SPI_NBITS_DUAL) ||
> + (opcode == HSSPI_OP_WRITE && t->tx_nbits == SPI_NBITS_DUAL)) {
> + opcode |= HSSPI_OP_MULTIBIT;
> +
> + if (t->rx_nbits == SPI_NBITS_DUAL) {
> + reg |= 1 << MODE_CTRL_MULTIDATA_RD_SIZE_SHIFT;
> + reg |= bs->prepend_cnt << MODE_CTRL_MULTIDATA_RD_STRT_SHIFT;
> + }
> + if (t->tx_nbits == SPI_NBITS_DUAL) {
> + reg |= 1 << MODE_CTRL_MULTIDATA_WR_SIZE_SHIFT;
> + reg |= bs->prepend_cnt << MODE_CTRL_MULTIDATA_WR_STRT_SHIFT;
> + }
> + }
> +
> + reg |= bs->prepend_cnt << MODE_CTRL_PREPENDBYTE_CNT_SHIFT;
> + __raw_writel(reg | 0xff,
> + bs->regs + HSSPI_PROFILE_MODE_CTRL_REG(chip_select));
> +
> + reinit_completion(&bs->done);
> + if (bs->prepend_cnt)
> + memcpy_toio(bs->fifo + HSSPI_OPCODE_LEN, bs->prepend_buf,
> + bs->prepend_cnt);
> + if (tx)
> + memcpy_toio(bs->fifo + HSSPI_OPCODE_LEN + bs->prepend_cnt, tx,
> + t->len);
> +
> + __raw_writew((u16)cpu_to_be16(opcode | t->len), bs->fifo);
> + /* enable interrupt */
> + if (bs->wait_mode == HSSPI_WAIT_MODE_INTR)
> + __raw_writel(HSSPI_PINGx_CMD_DONE(0), bs->regs + HSSPI_INT_MASK_REG);
> +
> + /* start the transfer */
> + reg = chip_select << PINGPONG_CMD_SS_SHIFT |
> + chip_select << PINGPONG_CMD_PROFILE_SHIFT |
> + PINGPONG_COMMAND_START_NOW;
> + __raw_writel(reg, bs->regs + HSSPI_PINGPONG_COMMAND_REG(0));
> +
> + if (bcm63xx_hsspi_wait_cmd(bs))
> + return -ETIMEDOUT;
> +
> + if (rx)
> + memcpy_fromio(rx, bs->fifo, t->len);
> +
> + return 0;
> +}
> +
> static void bcm63xx_hsspi_set_cs(struct bcm63xx_hsspi *bs, unsigned int cs,
> bool active)
> {
> @@ -215,10 +468,10 @@ static int bcm63xx_hsspi_do_txrx(struct spi_device *spi, struct spi_transfer *t)
> int step_size = HSSPI_BUFFER_LEN;
> const u8 *tx = t->tx_buf;
> u8 *rx = t->rx_buf;
> - u32 val = 0;
> - unsigned long limit;
> + u32 reg = 0;
>
> bcm63xx_hsspi_set_clk(bs, spi, t->speed_hz);
> +
> bcm63xx_hsspi_set_cs(bs, spi->chip_select, true);
>
> if (tx && rx)
> @@ -236,12 +489,12 @@ static int bcm63xx_hsspi_do_txrx(struct spi_device *spi, struct spi_transfer *t)
> opcode |= HSSPI_OP_MULTIBIT;
>
> if (t->rx_nbits == SPI_NBITS_DUAL)
> - val |= 1 << MODE_CTRL_MULTIDATA_RD_SIZE_SHIFT;
> + reg |= 1 << MODE_CTRL_MULTIDATA_RD_SIZE_SHIFT;
> if (t->tx_nbits == SPI_NBITS_DUAL)
> - val |= 1 << MODE_CTRL_MULTIDATA_WR_SIZE_SHIFT;
> + reg |= 1 << MODE_CTRL_MULTIDATA_WR_SIZE_SHIFT;
> }
>
> - __raw_writel(val | 0xff,
> + __raw_writel(reg | 0xff,
> bs->regs + HSSPI_PROFILE_MODE_CTRL_REG(chip_select));
>
> while (pending > 0) {
> @@ -260,28 +513,13 @@ static int bcm63xx_hsspi_do_txrx(struct spi_device *spi, struct spi_transfer *t)
> __raw_writel(HSSPI_PINGx_CMD_DONE(0),
> bs->regs + HSSPI_INT_MASK_REG);
>
> - /* start the transfer */
> - __raw_writel(!chip_select << PINGPONG_CMD_SS_SHIFT |
> - chip_select << PINGPONG_CMD_PROFILE_SHIFT |
> - PINGPONG_COMMAND_START_NOW,
> - bs->regs + HSSPI_PINGPONG_COMMAND_REG(0));
> + reg = !chip_select << PINGPONG_CMD_SS_SHIFT |
> + chip_select << PINGPONG_CMD_PROFILE_SHIFT |
> + PINGPONG_COMMAND_START_NOW;
> + __raw_writel(reg, bs->regs + HSSPI_PINGPONG_COMMAND_REG(0));
>
> - if (bs->wait_mode == HSSPI_WAIT_MODE_INTR) {
> - if (wait_for_completion_timeout(&bs->done, HZ) == 0)
> - goto err_timeout;
> - } else {
> - /* polling mode checks for status busy bit */
> - limit = jiffies + msecs_to_jiffies(HSSPI_POLL_STATUS_TIMEOUT_MS);
> - while (!time_after(jiffies, limit)) {
> - val = __raw_readl(bs->regs + HSSPI_PINGPONG_STATUS_REG(0));
> - if (val & HSSPI_PINGPONG_STATUS_SRC_BUSY)
> - cpu_relax();
> - else
> - break;
> - }
> - if (val & HSSPI_PINGPONG_STATUS_SRC_BUSY)
> - goto err_timeout;
> - }
> + if (bcm63xx_hsspi_wait_cmd(bs))
> + return -ETIMEDOUT;
>
> if (rx) {
> memcpy_fromio(rx, bs->fifo, curr_step);
> @@ -292,10 +530,6 @@ static int bcm63xx_hsspi_do_txrx(struct spi_device *spi, struct spi_transfer *t)
> }
>
> return 0;
> -
> -err_timeout:
> - dev_err(&bs->pdev->dev, "transfer timed out!\n");
> - return -ETIMEDOUT;
> }
>
> static int bcm63xx_hsspi_setup(struct spi_device *spi)
> @@ -344,9 +578,23 @@ static int bcm63xx_hsspi_transfer_one(struct spi_master *master,
> int status = -EINVAL;
> int dummy_cs;
> bool restore_polarity = true;
> + struct spi_transfer t_prepend;
>
> mutex_lock(&bs->msg_mutex);
> - /* This controller does not support keeping CS active during idle.
> + if (bcm63xx_check_msg_prependable(master, msg, &t_prepend)) {
> + status = bcm63xx_hsspi_do_prepend_txrx(spi, &t_prepend);
> + msg->actual_length += (t_prepend.len + bs->prepend_cnt);

why +=? shouldn't this be the only place in this case where this is set?

> + goto msg_done;
> + }
> +
> + if (bs->xfer_mode == HSSPI_XFER_MODE_PREPEND) {
> + dev_warn(&bs->pdev->dev,
> + "User set prepend mode but msg not prependable! Fail the xfer!\n");

If we are failing, this should be a dev_err, not a dev_warn

> + goto msg_done;
> + }

I think from a readability standpoint it would be better to move the
cs_workaround parts into their own function, and have this as

bool prependable = false;

if (bs->xfer_mode != HSSPI_XFER_MODE_DUMMYCS)
prependable = bcm63xx_prepare_prepend_transfer(...);

if (prependable) {
status = bcm63xx_hsspi_do_prepend_txrx(...);
msg->actual_legth += ...;
} else {
if (bs->xfer_mode == HSSPI_XFER_MODE_PREPEND) {
/* we may not use dummy cs */
dev_err(...);
status = -EINVAL;
} else {
status = bcm63xx_hsspi_do_dummy_cs_txrx(...);
}
}

with (bcm63xx_hsspi_do_dummy_cs_txrx being the proposed function name).

> +
> + /*
> + * This controller does not support keeping CS active during idle.
> * To work around this, we use the following ugly hack:
> *
> * a. Invert the target chip select's polarity so it will be active.
> @@ -364,6 +612,17 @@ static int bcm63xx_hsspi_transfer_one(struct spi_master *master,
> bcm63xx_hsspi_set_cs(bs, dummy_cs, true);
>
> list_for_each_entry(t, &msg->transfers, transfer_list) {
> + /*
> + * We are here because one of reasons below:
> + * a. Message is not prependable and in default auto xfer mode. This mean
> + * we fallback to dummy cs mode at maximum 25MHz safe clock rate.
> + * b. User set to use the dummy cs mode.
> + */
> + if (bs->xfer_mode == HSSPI_XFER_MODE_AUTO) {
> + if (t->speed_hz > HSSPI_MAX_SYNC_CLOCK)
> + t->speed_hz = HSSPI_MAX_SYNC_CLOCK;

OTOH, this may be a point where a dev_warn (once?) might be a good
idea, since the device may depend on a certain speed to avoid buffer
overruns (e.g. audio streams - not sure if that exists), so a warning
that the transfer speed was reduced will help identifying the source.

> + }
> +
> status = bcm63xx_hsspi_do_txrx(spi, t);
> if (status)
> break;
> @@ -396,6 +655,7 @@ static int bcm63xx_hsspi_transfer_one(struct spi_master *master,
> if (restore_polarity)
> bcm63xx_hsspi_set_cs(bs, spi->chip_select, false);
>
> +msg_done:
> mutex_unlock(&bs->msg_mutex);
> msg->status = status;
> spi_finalize_current_message(master);
> @@ -490,6 +750,11 @@ static int bcm63xx_hsspi_probe(struct platform_device *pdev)
> bs->speed_hz = rate;
> bs->fifo = (u8 __iomem *)(bs->regs + HSSPI_FIFO_REG(0));
> bs->wait_mode = HSSPI_WAIT_MODE_POLLING;
> + bs->prepend_buf = devm_kzalloc(dev, HSSPI_BUFFER_LEN, GFP_KERNEL);
> + if (!bs->prepend_buf) {
> + ret = -ENOMEM;
> + goto out_put_master;
> + }
>
> mutex_init(&bs->bus_mutex);
> mutex_init(&bs->msg_mutex);
> @@ -508,6 +773,9 @@ static int bcm63xx_hsspi_probe(struct platform_device *pdev)
> master->num_chipselect = num_cs;
> master->setup = bcm63xx_hsspi_setup;
> master->transfer_one_message = bcm63xx_hsspi_transfer_one;
> + master->max_transfer_size = bcm63xx_hsspi_max_message_size;
> + master->max_message_size = bcm63xx_hsspi_max_message_size;
> +
> master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH |
> SPI_RX_DUAL | SPI_TX_DUAL;
> master->bits_per_word_mask = SPI_BPW_MASK(8);
> --
> 2.37.3
>

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