linux-kernel - [PATCH 4.0 076/105] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

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Message-Id: <20150619203600.422383901@linuxfoundation.org>
Date:	Fri, 19 Jun 2015 13:36:06 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Jim Bride <jim.bride@...ux.intel.com>,
	Jani Nikula <jani.nikula@...el.com>
Subject: [PATCH 4.0 076/105] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

4.0-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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/i915/intel_dp.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -881,10 +881,8 @@ intel_dp_aux_ch(struct intel_dp *intel_d
 				      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) {
@@ -893,6 +891,7 @@ intel_dp_aux_ch(struct intel_dp *intel_d
 		goto out;
 	}
 
+done:
 	/* Check for timeout or receive error.
 	 * Timeouts occur when the sink is not connected
 	 */


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