linux-kernel - [PATCH 3.16.y-ckt 17/71] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

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Date:	Thu, 25 Jun 2015 11:01:56 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Jim Bride <jim.bride@...ux.intel.com>,
	Jani Nikula <jani.nikula@...el.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 17/71] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

3.16.7-ckt14 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jim Bride <jim.bride@...ux.intel.com>

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@...ux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@...el.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.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
 	 */
--
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