[Intel-gfx] [PATCH 2/6] drm/i915: Add a delay in Displayport AUX transactions for compliance testing

[Todd Previte]

Several compliance tests require that follow-up AUX transactions (after a
failure or no response) are not resent sooner than 400us later. Add a 400us
delay to the response time of any failed transaction to account for this.

Signed-off-by: Todd Previte <tprevite at gmail.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 3bd1780..43fcabe 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -561,8 +561,12 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 				   DP_AUX_CH_CTL_RECEIVE_ERROR);
 
 			if (status & (DP_AUX_CH_CTL_TIME_OUT_ERROR |
-				      DP_AUX_CH_CTL_RECEIVE_ERROR))
+				      DP_AUX_CH_CTL_RECEIVE_ERROR)) {
+				/* 400us delay between transactions for errors/timeouts
+				   required for DP compliance testing */
+				udelay(400);
 				continue;
+			}
 			if (status & DP_AUX_CH_CTL_DONE)
 				break;
 		}
-- 
1.9.1