[Intel-gfx] [PATCH 04/10] drm/i915: Add a delay in Displayport AUX transactions for compliance testing

[Todd Previte]

The Displayport Link Layer Compliance Testing Specification 1.2 rev 1.1 specifies that
repeated AUX transactions after a failure (no response / invalid response) must have
a minimum delay of 400us before the resend can occur. Tests 4.2.1.1 and 4.2.1.2 are two
tests that require this specifically.

Signed-off-by: Todd Previte <tprevite at gmail.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 952dfa3..a7acc61 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -799,9 +799,14 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 				   DP_AUX_CH_CTL_TIME_OUT_ERROR |
 				   DP_AUX_CH_CTL_RECEIVE_ERROR);
 
+			/* DP compliance requires 400us delay for errors
+			   and timeouts (DP CTS 1.2 Core Rev 1.1, 4.2.1.1
+			   & 4.2.1.2) */
 			if (status & (DP_AUX_CH_CTL_TIME_OUT_ERROR |
-				      DP_AUX_CH_CTL_RECEIVE_ERROR))
+				      DP_AUX_CH_CTL_RECEIVE_ERROR)) {
+				udelay(400);
 				continue;
+			}
 			if (status & DP_AUX_CH_CTL_DONE)
 				break;
 		}
-- 
1.9.1