[3.16.y-ckt stable] Patch "drm/i915/hsw: Fix workaround for server AUX channel clock divisor" 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/i915/hsw: Fix workaround for server AUX channel clock divisor

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/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt14.

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 a162116a8212a49e8214b75e6e474962a3a74200 Mon Sep 17 00:00:00 2001
From: Jim Bride <jim.bride at linux.intel.com>
Date: Wed, 27 May 2015 10:21:48 -0700
Subject: drm/i915/hsw: Fix workaround for server AUX channel clock divisor

commit e058c945e03a629c99606452a6931f632dd28903 upstream.

According to the HSW b-spec we need to try clock divisors of 63
and 72, each 3 or more times, when attempting DP AUX channel
communication on a server chipset.  This actually wasn't happening
due to a short-circuit that only checked the DP_AUX_CH_CTL_DONE bit
in status rather than checking that the operation was done and
that DP_AUX_CH_CTL_TIME_OUT_ERROR was not set.

[v2] Implemented alternate solution suggested by Jani Nikula.

Signed-off-by: Jim Bride <jim.bride at linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index d2f1431eb428..b5660eb078f6 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -597,10 +597,8 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 				      DP_AUX_CH_CTL_RECEIVE_ERROR))
 				continue;
 			if (status & DP_AUX_CH_CTL_DONE)
-				break;
+				goto done;
 		}
-		if (status & DP_AUX_CH_CTL_DONE)
-			break;
 	}

 	if ((status & DP_AUX_CH_CTL_DONE) == 0) {
@@ -609,6 +607,7 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 		goto out;
 	}

+done:
 	/* Check for timeout or receive error.
 	 * Timeouts occur when the sink is not connected
 	 */