linux-kernel - [PATCH 3.12 021/124] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

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Message-Id: <1dec7c0ba1c46a8a6008daf90afc05b5805582f1.1438076484.git.jslaby@suse.cz>
Date:	Tue, 28 Jul 2015 11:42:35 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Jim Bride <jim.bride@...ux.intel.com>,
	Jani Nikula <jani.nikula@...el.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 021/124] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

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

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

===============

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: Jiri Slaby <jslaby@...e.cz>
---
 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 b0191f25cd55..5a9ef60ab625 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -394,10 +394,8 @@ 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) {
@@ -406,6 +404,7 @@ 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
 	 */
-- 
2.4.6

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