Re: [PATCH] fpga: microchip-spi: move SPI I/O buffers out of stack

From: Xu Yilun
Date: Mon Dec 26 2022 - 04:07:07 EST

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On 2022-12-23 at 15:38:54 +0300, Ivan Bornyakov wrote:
> As spi-summary doc says:
> > I/O buffers use the usual Linux rules, and must be DMA-safe.
> > You'd normally allocate them from the heap or free page pool.
> > Don't use the stack, or anything that's declared "static".
>
> Replace spi_write() with spi_write_then_read(), which is dma-safe for
> on-stack buffers. Use allocated buffers for transfers used in
> spi_sync_transfer().
>
> Although everything works OK with stack-located I/O buffers, better
> follow the doc to be safe.
>
> While at it, replace busy loop in mpf_poll_status() routine with
> read_poll_timeout() macro. Original busy loop is not too reliable, as it
> takes different times on different systems.

Yes, I see there are several intents in this patch, spi dma safe fix, busy
loop change, coding style ...

Could you help split them, one change for each patch?

>
> Fixes: 5f8d4a900830 ("fpga: microchip-spi: add Microchip MPF FPGA manager")
> Signed-off-by: Ivan Bornyakov <i.bornyakov@xxxxxxxxxxx>
> ---
> drivers/fpga/microchip-spi.c | 145 +++++++++++++++++++----------------
> 1 file changed, 80 insertions(+), 65 deletions(-)
>
> diff --git a/drivers/fpga/microchip-spi.c b/drivers/fpga/microchip-spi.c
> index 7436976ea904..dfb4e071db86 100644
> --- a/drivers/fpga/microchip-spi.c
> +++ b/drivers/fpga/microchip-spi.c
> @@ -6,6 +6,7 @@
> #include <asm/unaligned.h>
> #include <linux/delay.h>
> #include <linux/fpga/fpga-mgr.h>
> +#include <linux/iopoll.h>
> #include <linux/module.h>
> #include <linux/of_device.h>
> #include <linux/spi/spi.h>
> @@ -33,7 +34,6 @@
>
> #define MPF_BITS_PER_COMPONENT_SIZE 22
>
> -#define MPF_STATUS_POLL_RETRIES 10000
> #define MPF_STATUS_BUSY BIT(0)
> #define MPF_STATUS_READY BIT(1)
> #define MPF_STATUS_SPI_VIOLATION BIT(2)
> @@ -42,46 +42,55 @@
> struct mpf_priv {
> struct spi_device *spi;
> bool program_mode;
> + u8 *tx;
> + u8 *rx;

u8 tx __aligned(ARCH_KMALLOC_MINALIGN);
u8 rx;

Is that OK?

> };
>
> -static int mpf_read_status(struct spi_device *spi)
> +static int mpf_read_status(struct mpf_priv *priv)
> {
> - u8 status = 0, status_command = MPF_SPI_READ_STATUS;
> - struct spi_transfer xfers[2] = { 0 };
> - int ret;
> -
> /*
> * HW status is returned on MISO in the first byte after CS went
> * active. However, first reading can be inadequate, so we submit
> * two identical SPI transfers and use result of the later one.
> */
> - xfers[0].tx_buf = &status_command;
> - xfers[1].tx_buf = &status_command;
> - xfers[0].rx_buf = &status;
> - xfers[1].rx_buf = &status;
> - xfers[0].len = 1;
> - xfers[1].len = 1;
> - xfers[0].cs_change = 1;
> + struct spi_transfer xfers[2] = {
> + {
> + .tx_buf = priv->tx,
> + .rx_buf = priv->rx,
> + .len = 1,
> + .cs_change = 1,
> + }, {
> + .tx_buf = priv->tx,
> + .rx_buf = priv->rx,
> + .len = 1,
> + },
> + };
> + u8 status;
> + int ret;
>
> - ret = spi_sync_transfer(spi, xfers, 2);
> + *priv->tx = MPF_SPI_READ_STATUS;
> +
> + ret = spi_sync_transfer(priv->spi, xfers, 2);
> + if (ret)
> + return ret;
> +
> + status = *priv->rx;
>
> if ((status & MPF_STATUS_SPI_VIOLATION) ||
> (status & MPF_STATUS_SPI_ERROR))
> - ret = -EIO;
> + return -EIO;
>
> - return ret ? : status;
> + return status;
> }
>
> static enum fpga_mgr_states mpf_ops_state(struct fpga_manager *mgr)
> {
> struct mpf_priv *priv = mgr->priv;
> - struct spi_device *spi;
> bool program_mode;
> int status;
>
> - spi = priv->spi;
> program_mode = priv->program_mode;
> - status = mpf_read_status(spi);
> + status = mpf_read_status(priv);
>
> if (!program_mode && !status)
> return FPGA_MGR_STATE_OPERATING;
> @@ -186,51 +195,47 @@ static int mpf_ops_parse_header(struct fpga_manager *mgr,
> }
>
> /* Poll HW status until busy bit is cleared and mask bits are set. */
> -static int mpf_poll_status(struct spi_device *spi, u8 mask)
> +static int mpf_poll_status(struct mpf_priv *priv, u8 mask)
> {
> - int status, retries = MPF_STATUS_POLL_RETRIES;
> -
> - while (retries--) {
> - status = mpf_read_status(spi);
> - if (status < 0)
> - return status;
> + int ret, status;
>
> - if (status & MPF_STATUS_BUSY)
> - continue;
> -
> - if (!mask || (status & mask))
> - return status;
> - }
> + ret = read_poll_timeout(mpf_read_status, status,
> + (status < 0) ||
> + (!(status & MPF_STATUS_BUSY) &&
> + (!mask || (status & mask))),
> + 0, 2 * USEC_PER_SEC, false, priv);

use a MACRO for timeout value.

Thanks,
Yilun

> + if (ret < 0)
> + return ret;
>
> - return -EBUSY;
> + return status;
> }
>
> -static int mpf_spi_write(struct spi_device *spi, const void *buf, size_t buf_size)
> +static int mpf_spi_write(struct mpf_priv *priv, const void *buf, size_t buf_size)
> {
> - int status = mpf_poll_status(spi, 0);
> + int status = mpf_poll_status(priv, 0);
>
> if (status < 0)
> return status;
>
> - return spi_write(spi, buf, buf_size);
> + return spi_write_then_read(priv->spi, buf, buf_size, NULL, 0);
> }
>
> -static int mpf_spi_write_then_read(struct spi_device *spi,
> +static int mpf_spi_write_then_read(struct mpf_priv *priv,
> const void *txbuf, size_t txbuf_size,
> void *rxbuf, size_t rxbuf_size)
> {
> const u8 read_command[] = { MPF_SPI_READ_DATA };
> int ret;
>
> - ret = mpf_spi_write(spi, txbuf, txbuf_size);
> + ret = mpf_spi_write(priv, txbuf, txbuf_size);
> if (ret)
> return ret;
>
> - ret = mpf_poll_status(spi, MPF_STATUS_READY);
> + ret = mpf_poll_status(priv, MPF_STATUS_READY);
> if (ret < 0)
> return ret;
>
> - return spi_write_then_read(spi, read_command, sizeof(read_command),
> + return spi_write_then_read(priv->spi, read_command, sizeof(read_command),
> rxbuf, rxbuf_size);
> }
>
> @@ -242,7 +247,6 @@ static int mpf_ops_write_init(struct fpga_manager *mgr,
> const u8 isc_en_command[] = { MPF_SPI_ISC_ENABLE };
> struct mpf_priv *priv = mgr->priv;
> struct device *dev = &mgr->dev;
> - struct spi_device *spi;
> u32 isc_ret = 0;
> int ret;
>
> @@ -251,9 +255,7 @@ static int mpf_ops_write_init(struct fpga_manager *mgr,
> return -EOPNOTSUPP;
> }
>
> - spi = priv->spi;
> -
> - ret = mpf_spi_write_then_read(spi, isc_en_command, sizeof(isc_en_command),
> + ret = mpf_spi_write_then_read(priv, isc_en_command, sizeof(isc_en_command),
> &isc_ret, sizeof(isc_ret));
> if (ret || isc_ret) {
> dev_err(dev, "Failed to enable ISC: spi_ret %d, isc_ret %u\n",
> @@ -261,7 +263,7 @@ static int mpf_ops_write_init(struct fpga_manager *mgr,
> return -EFAULT;
> }
>
> - ret = mpf_spi_write(spi, program_mode, sizeof(program_mode));
> + ret = mpf_spi_write(priv, program_mode, sizeof(program_mode));
> if (ret) {
> dev_err(dev, "Failed to enter program mode: %d\n", ret);
> return ret;
> @@ -272,13 +274,32 @@ static int mpf_ops_write_init(struct fpga_manager *mgr,
> return 0;
> }
>
> +static int mpf_spi_frame_write(struct mpf_priv *priv, const char *buf)
> +{
> + struct spi_transfer xfers[2] = {
> + {
> + .tx_buf = priv->tx,
> + .len = 1,
> + }, {
> + .tx_buf = buf,
> + .len = MPF_SPI_FRAME_SIZE,
> + },
> + };
> + int ret;
> +
> + ret = mpf_poll_status(priv, 0);
> + if (ret < 0)
> + return ret;
> +
> + *priv->tx = MPF_SPI_FRAME;
> +
> + return spi_sync_transfer(priv->spi, xfers, ARRAY_SIZE(xfers));
> +}
> +
> static int mpf_ops_write(struct fpga_manager *mgr, const char *buf, size_t count)
> {
> - u8 spi_frame_command[] = { MPF_SPI_FRAME };
> - struct spi_transfer xfers[2] = { 0 };
> struct mpf_priv *priv = mgr->priv;
> struct device *dev = &mgr->dev;
> - struct spi_device *spi;
> int ret, i;
>
> if (count % MPF_SPI_FRAME_SIZE) {
> @@ -287,19 +308,8 @@ static int mpf_ops_write(struct fpga_manager *mgr, const char *buf, size_t count
> return -EINVAL;
> }
>
> - spi = priv->spi;
> -
> - xfers[0].tx_buf = spi_frame_command;
> - xfers[0].len = sizeof(spi_frame_command);
> -
> for (i = 0; i < count / MPF_SPI_FRAME_SIZE; i++) {
> - xfers[1].tx_buf = buf + i * MPF_SPI_FRAME_SIZE;
> - xfers[1].len = MPF_SPI_FRAME_SIZE;
> -
> - ret = mpf_poll_status(spi, 0);
> - if (ret >= 0)
> - ret = spi_sync_transfer(spi, xfers, ARRAY_SIZE(xfers));
> -
> + ret = mpf_spi_frame_write(priv, buf + i * MPF_SPI_FRAME_SIZE);
> if (ret) {
> dev_err(dev, "Failed to write bitstream frame %d/%zu\n",
> i, count / MPF_SPI_FRAME_SIZE);
> @@ -317,12 +327,9 @@ static int mpf_ops_write_complete(struct fpga_manager *mgr,
> const u8 release_command[] = { MPF_SPI_RELEASE };
> struct mpf_priv *priv = mgr->priv;
> struct device *dev = &mgr->dev;
> - struct spi_device *spi;
> int ret;
>
> - spi = priv->spi;
> -
> - ret = mpf_spi_write(spi, isc_dis_command, sizeof(isc_dis_command));
> + ret = mpf_spi_write(priv, isc_dis_command, sizeof(isc_dis_command));
> if (ret) {
> dev_err(dev, "Failed to disable ISC: %d\n", ret);
> return ret;
> @@ -330,7 +337,7 @@ static int mpf_ops_write_complete(struct fpga_manager *mgr,
>
> usleep_range(1000, 2000);
>
> - ret = mpf_spi_write(spi, release_command, sizeof(release_command));
> + ret = mpf_spi_write(priv, release_command, sizeof(release_command));
> if (ret) {
> dev_err(dev, "Failed to exit program mode: %d\n", ret);
> return ret;
> @@ -361,6 +368,14 @@ static int mpf_probe(struct spi_device *spi)
> if (!priv)
> return -ENOMEM;
>
> + priv->tx = devm_kmalloc(dev, 1, GFP_KERNEL);
> + if (!priv->tx)
> + return -ENOMEM;
> +
> + priv->rx = devm_kmalloc(dev, 1, GFP_KERNEL);
> + if (!priv->rx)
> + return -ENOMEM;
> +
> priv->spi = spi;
>
> mgr = devm_fpga_mgr_register(dev, "Microchip Polarfire SPI FPGA Manager",
> --
> 2.38.2
>
>

Next message: Daniil Tatianin: "[RESEND PATCH v2] cxgbi: move cxgbi_ddp_set_one_ppod to cxgb_ppm and remove its duplicate"
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