[PATCH v4 07/11] drm/bridge: cdns-dsi: Reset the DCS write FIFO

[Aradhya Bhatia]

If any normal DCS write command has already been transmitted prior to
transmitting any Zero-Parameter DCS command, then it is necessary to
clear the TX FIFO by resetting it. Otherwise, the FIFO points to another
location, and the DCS command transmits unnecessary data causing the
panel to not work[0].

Allow the DCS Write FIFO in the cdns-dsi controller to reset as a rule,
before any DCS packet is transmitted to the DSI peripheral.

[0]: Section 12.6.5.7.5.2: "Command Mode Settings" in TDA4VM Technical
     Reference Manual: https://www.ti.com/lit/zip/spruil1

Signed-off-by: Aradhya Bhatia <a-bhatia1 at ti.com>
---
 drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index 126e4bccd868..cad0c1478ef0 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -1018,6 +1018,9 @@ static ssize_t cdns_dsi_transfer(struct mipi_dsi_host *host,
 
 	cdns_dsi_init_link(dsi);
 
+	/* Reset the DCS Write FIFO */
+	writel(0x00, dsi->regs + DIRECT_CMD_FIFO_RST);
+
 	ret = mipi_dsi_create_packet(&packet, msg);
 	if (ret)
 		goto out;
-- 
2.34.1