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@xxxxxxxxxxxx>
---
v1->v2: Offline discussed with Xin Ji, it's better to clear the bit on
read commands only.
---
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 633618bafd75d3..2805e9bed2c2f4 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 */
--
2.35.1.265.g69c8d7142f-goog
