From: Dave Airlie <airlied@xxxxxxxxxx>
At least on two MST devices I've tested with, when
they are link training downstream, they are totally
unable to handle aux ch msgs, so they defer like nuts.
I tried 16, it wasn't enough, 32 seems better.
This fixes one Dell 4k monitor and one of the
MST hubs.
v1.1: fixup comment (Tom).
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
---
drivers/gpu/drm/drm_dp_helper.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 959e207..79968e3 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -186,10 +186,11 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
/*
* The specification doesn't give any recommendation on how often to
- * retry native transactions, so retry 7 times like for I2C-over-AUX
- * transactions.
+ * retry native transactions. We used to retry 7 times like for
+ * aux i2c transactions but real world devices this wasn't
+ * sufficient, bump to 32 which makes Dell 4k monitors happier.
*/
- for (retry = 0; retry < 7; retry++) {
+ for (retry = 0; retry < 32; retry++) {
mutex_lock(&aux->hw_mutex);
err = aux->transfer(aux, &msg);
--
2.1.0
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