[PATCH 3.14 37/44] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

Greg Kroah-Hartman
2015-06-19T21:00:27Z

From: Jim Bride <jim.bride@linux.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@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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
@@ -481,10 +481,8 @@ 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) {
@@ -493,6 +491,7 @@ 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
*/