From 75dd15e405e189ae2b3a8f2d3dee21d7579bb4ce Mon Sep 17 00:00:00 2001
From: Hsin-Yi Wang <hsinyi@chromium.org>
Date: Thu, 17 Feb 2022 16:22:25 +0800
Subject: drm/bridge: Clear the DP_AUX_I2C_MOT bit passed in aux read command.
Git-commit: c0bbed9051b6eb293be6128d060bb49e999ef7d4
Patch-mainline: v5.18-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225

If the previous transfer didn't end with a command without DP_AUX_I2C_MOT,
the next read trasnfer will miss the first byte. But if the command in
previous transfer is requested with length 0, it's a no-op to anx7625
since it can't process this command. anx7625 requires the last command
to be read command with length > 0.

It's observed that if we clear the DP_AUX_I2C_MOT in read transfer, we
can still get correct data. Clear the read commands with DP_AUX_I2C_MOT
bit to fix this issue.

Fixes: adca62ec370c ("drm/bridge: anx7625: Support reading edid through aux channel")
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Xin Ji <xji@analogixsemi.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220217082224.1823916-1-hsinyi@chromium.org
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/bridge/analogix/anx7625.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
index 9aab879a8851..31ecf5626f1d 100644
--- a/drivers/gpu/drm/bridge/analogix/anx7625.c
+++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
@@ -253,6 +253,8 @@ static int anx7625_aux_trans(struct anx7625_data *ctx, u8 op, u32 address,
 	addrm = (address >> 8) & 0xFF;
 	addrh = (address >> 16) & 0xFF;
 
+	if (!is_write)
+		op &= ~DP_AUX_I2C_MOT;
 	cmd = DPCD_CMD(len, op);
 
 	/* Set command and length */
-- 
2.38.1