drm/i915/hsw: Fix workaround for server AUX channel clock divisor

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.

Cc: stable@vger.kernel.org
Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index f27346e..d714a4b 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -880,10 +880,8 @@ 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) {
@@ -892,6 +890,7 @@ 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
         */