This is a note to let you know that I've just added the patch titled
drm/dp: retry AUX transactions 32 times (v1.1)
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-dp-retry-aux-transactions-32-times-v1.1.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 19a93f042fc241ecdf98543cedfe7c171f8cdf53 Mon Sep 17 00:00:00 2001
From: Dave Airlie <airlied@xxxxxxxxxx>
Date: Wed, 26 Nov 2014 13:13:09 +1000
Subject: drm/dp: retry AUX transactions 32 times (v1.1)
From: Dave Airlie <airlied@xxxxxxxxxx>
commit 19a93f042fc241ecdf98543cedfe7c171f8cdf53 upstream.
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).
Acked-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_dp_helper.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -378,10 +378,11 @@ static int drm_dp_dpcd_access(struct drm
/*
* 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);
Patches currently in stable-queue which might be from airlied@xxxxxxxxxx are
queue-3.18/drm-ttm-avoid-memory-allocation-from-shrinker-functions.patch
queue-3.18/drm-dp-retry-aux-transactions-32-times-v1.1.patch
queue-3.18/drm-fb_helper-move-deferred-fb-checking-into-restore-mode-v2.patch
queue-3.18/drm-dp-mst-remove-branches-before-dropping-the-reference.patch
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