drm/mcde: Retry DSI read/write transactions

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.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Stephan Gerhold <stephan@gerhold.net>
Cc: Stephan Gerhold <stephan@gerhold.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20200814194451.3494294-1-linus.walleij@linaro.org

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,
+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++;
+	}
+	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);