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

[Linus Walleij]

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 two times.

Cc: Stephan Gerhold <stephan at gerhold.net>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
 drivers/gpu/drm/mcde/mcde_dsi.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/mcde/mcde_dsi.c b/drivers/gpu/drm/mcde/mcde_dsi.c
index 337c4c5e3947..76fecd7ab658 100644
--- a/drivers/gpu/drm/mcde/mcde_dsi.c
+++ b/drivers/gpu/drm/mcde/mcde_dsi.c
@@ -207,8 +207,8 @@ 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 ssize_t mcde_dsi_host_transfer_commit(struct mipi_dsi_host *host,
+					     const struct mipi_dsi_msg *msg)
 {
 	struct mcde_dsi *d = host_to_mcde_dsi(host);
 	const u32 loop_delay_us = 10; /* us */
@@ -353,6 +353,23 @@ static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,
 	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);
+	int retries = 2;
+	ssize_t ret;
+
+	while (retries--) {
+		ret = mcde_dsi_host_transfer_commit(host, msg);
+		if (ret >= 0)
+			return ret;
+	}
+
+	dev_err(d->dev, "gave up transfer after retrying\n");
+	return ret;
+}
+
 static const struct mipi_dsi_host_ops mcde_dsi_host_ops = {
 	.attach = mcde_dsi_host_attach,
 	.detach = mcde_dsi_host_detach,
-- 
2.26.2