[3.16.y-ckt stable] Patch "drm/dp: retry AUX transactions 32 times (v1.1)" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    drm/dp: retry AUX transactions 32 times (v1.1)

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt4.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 7f333147db36c10c535b7161b5d954fc6f82531d Mon Sep 17 00:00:00 2001
From: Dave Airlie <airlied at redhat.com>
Date: Wed, 26 Nov 2014 13:13:09 +1000
Subject: drm/dp: retry AUX transactions 32 times (v1.1)

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 at amd.com>
Signed-off-by: Dave Airlie <airlied at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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 08e33b8b13a4..9f59c9027ebe 100644
--- 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_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);
--
2.1.4