Re: [PATCH v2] drm/mcde: Retry DSI read/write transactions

On Fri, Aug 14, 2020 at 09:44:51PM +0200, Linus Walleij wrote:

The vendor driver makes a few retries on read DSI transactions, something that is needed especially in case of read (such as reading the panel MTP ID) while the panel is running in video mode. This happens on the Samsung s6e63m0 panel on the Golden device.

Retry reads and writes alike three times.

Cc: Stephan Gerhold stephan@gerhold.net Signed-off-by: Linus Walleij linus.walleij@linaro.org

---

ChangeLog v1->v2:

• Retry three times.
• Only retry the actual command transmission like the vendor driver does, no need to set up all registers and do checks all over. Break out a part of the mcde_dsi_host_transfer() function to achieve this.

---

drivers/gpu/drm/mcde/mcde_dsi.c | 158 +++++++++++++++++++------------- 1 file changed, 92 insertions(+), 66 deletions(-)

diff --git a/drivers/gpu/drm/mcde/mcde_dsi.c b/drivers/gpu/drm/mcde/mcde_dsi.c index 4ce8cc5f0be2..b3c5d3cbda92 100644 --- a/drivers/gpu/drm/mcde/mcde_dsi.c +++ b/drivers/gpu/drm/mcde/mcde_dsi.c @@ -208,79 +208,16 @@ static int mcde_dsi_host_detach(struct mipi_dsi_host *host, (type == MIPI_DSI_GENERIC_READ_REQUEST_2_PARAM) || \ (type == MIPI_DSI_DCS_READ))

-static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,

• 		      const struct mipi_dsi_msg *msg)
  

+static int mcde_dsi_execute_transfer(struct mcde_dsi *d,

• 		     const struct mipi_dsi_msg *msg)
  

{

• struct mcde_dsi *d = host_to_mcde_dsi(host); const u32 loop_delay_us = 10; /* us */
• const u8 *tx = msg->tx_buf; u32 loop_counter; size_t txlen = msg->tx_len; size_t rxlen = msg->rx_len;

• int i; u32 val; int ret;

• int i;

• if (txlen > 16) {

• dev_err(d->dev,
  

• 	"dunno how to write more than 16 bytes yet\n");
  

• return -EIO;
  

• }

• if (rxlen > 4) {

• dev_err(d->dev,
  

• 	"dunno how to read more than 4 bytes yet\n");
  

• return -EIO;
  

• }

• dev_dbg(d->dev,

• "message to channel %d, write %zd bytes read %zd bytes\n",
  

• msg->channel, txlen, rxlen);
  

• /* Command "nature" */

• if (MCDE_DSI_HOST_IS_READ(msg->type))

• /* MCTL_MAIN_DATA_CTL already set up */
  

• val = DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_NAT_READ;
  

• else

• val = DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_NAT_WRITE;
  

• /*

• * More than 2 bytes will not fit in a single packet, so it's
  

• * time to set the "long not short" bit. One byte is used by
  

• * the MIPI DCS command leaving just one byte for the payload
  

• * in a short package.
  

• */
  

• if (mipi_dsi_packet_format_is_long(msg->type))

• val |= DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_LONGNOTSHORT;
  

• val |= 0 << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_ID_SHIFT;

• val |= txlen << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_SIZE_SHIFT;

• val |= DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_LP_EN;

• val |= msg->type << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_HEAD_SHIFT;

• writel(val, d->regs + DSI_DIRECT_CMD_MAIN_SETTINGS);

• /* MIPI DCS command is part of the data */

• if (txlen > 0) {

• val = 0;
  

• for (i = 0; i < 4 && i < txlen; i++)
  

• 	val |= tx[i] << (i * 8);
  

• }

• writel(val, d->regs + DSI_DIRECT_CMD_WRDAT0);

• if (txlen > 4) {

• val = 0;
  

• for (i = 0; i < 4 && (i + 4) < txlen; i++)
  

• 	val |= tx[i + 4] << (i * 8);
  

• writel(val, d->regs + DSI_DIRECT_CMD_WRDAT1);
  

• }

• if (txlen > 8) {

• val = 0;
  

• for (i = 0; i < 4 && (i + 8) < txlen; i++)
  

• 	val |= tx[i + 8] << (i * 8);
  

• writel(val, d->regs + DSI_DIRECT_CMD_WRDAT2);
  

• }

• if (txlen > 12) {

• val = 0;
  

• for (i = 0; i < 4 && (i + 12) < txlen; i++)
  

• 	val |= tx[i + 12] << (i * 8);
  

• writel(val, d->regs + DSI_DIRECT_CMD_WRDAT3);
  

• }

  writel(~0, d->regs + DSI_DIRECT_CMD_STS_CLR); writel(~0, d->regs + DSI_CMD_MODE_STS_CLR);

@@ -297,6 +234,7 @@ static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host, usleep_range(loop_delay_us, (loop_delay_us * 3) / 2); if (!loop_counter) { dev_err(d->dev, "DSI read timeout!\n");

• 	/* Set exit code and retry */
  return -ETIME;
  

  } } else {

@@ -307,6 +245,7 @@ static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host, usleep_range(loop_delay_us, (loop_delay_us * 3) / 2);

if (!loop_counter) {

• 	/* Set exit code and retry */
  dev_err(d->dev, "DSI write timeout!\n");
  return -ETIME;
  

  }

@@ -348,6 +287,93 @@ static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host, ret = rdsz; }

• /* Successful transmission */
• return ret;

+}

+static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,

• 		      const struct mipi_dsi_msg *msg)
  

+{

• struct mcde_dsi *d = host_to_mcde_dsi(host);
• const u8 *tx = msg->tx_buf;
• size_t txlen = msg->tx_len;
• size_t rxlen = msg->rx_len;
• unsigned int retries = 0;
• u32 val;
• int ret;
• int i;
• if (txlen > 16) {

• dev_err(d->dev,
  

• 	"dunno how to write more than 16 bytes yet\n");
  

• return -EIO;
  

• }
• if (rxlen > 4) {

• dev_err(d->dev,
  

• 	"dunno how to read more than 4 bytes yet\n");
  

• return -EIO;
  

• }
• dev_dbg(d->dev,

• "message to channel %d, write %zd bytes read %zd bytes\n",
  

• msg->channel, txlen, rxlen);
  

• /* Command "nature" */
• if (MCDE_DSI_HOST_IS_READ(msg->type))

• /* MCTL_MAIN_DATA_CTL already set up */
  

• val = DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_NAT_READ;
  

• else

• val = DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_NAT_WRITE;
  

• /*

• * More than 2 bytes will not fit in a single packet, so it's
  

• * time to set the "long not short" bit. One byte is used by
  

• * the MIPI DCS command leaving just one byte for the payload
  

• * in a short package.
  

• */
  

• if (mipi_dsi_packet_format_is_long(msg->type))

• val |= DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_LONGNOTSHORT;
  

• val |= 0 << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_ID_SHIFT;
• val |= txlen << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_SIZE_SHIFT;
• val |= DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_LP_EN;
• val |= msg->type << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_HEAD_SHIFT;
• writel(val, d->regs + DSI_DIRECT_CMD_MAIN_SETTINGS);
• /* MIPI DCS command is part of the data */
• if (txlen > 0) {

• val = 0;
  

• for (i = 0; i < 4 && i < txlen; i++)
  

• 	val |= tx[i] << (i * 8);
  

• }
• writel(val, d->regs + DSI_DIRECT_CMD_WRDAT0);
• if (txlen > 4) {

• val = 0;
  

• for (i = 0; i < 4 && (i + 4) < txlen; i++)
  

• 	val |= tx[i + 4] << (i * 8);
  

• writel(val, d->regs + DSI_DIRECT_CMD_WRDAT1);
  

• }
• if (txlen > 8) {

• val = 0;
  

• for (i = 0; i < 4 && (i + 8) < txlen; i++)
  

• 	val |= tx[i + 8] << (i * 8);
  

• writel(val, d->regs + DSI_DIRECT_CMD_WRDAT2);
  

• }
• if (txlen > 12) {

• val = 0;
  

• for (i = 0; i < 4 && (i + 12) < txlen; i++)
  

• 	val |= tx[i + 12] << (i * 8);
  

• writel(val, d->regs + DSI_DIRECT_CMD_WRDAT3);
  

• }
• while (retries < 3) {

• ret = mcde_dsi_execute_transfer(d, msg);
  

• if (ret >= 0)
  

• 	break;
  

• retries++;
  

• }

It might be a bit nicer to write this as a for loop, i.e.

for (retries = 0; retries < 3; retries++) { ret = mcde_dsi_execute_transfer(d, msg); if (ret >= 0) break; }

But I guess it does not make much of a difference here.

Just a thought, looks good to me otherwise! Reviewed-by: Stephan Gerhold stephan@gerhold.net

Thanks! Stephan

• if (ret < 0 && retries)

• dev_err(d->dev, "gave up after %d retries\n", retries);
  

• /* Clear any errors */ writel(~0, d->regs + DSI_DIRECT_CMD_STS_CLR); writel(~0, d->regs + DSI_CMD_MODE_STS_CLR);

-- 2.26.2