From 74ebf294a1dd816bdc248ac733009a8915d59eb5 Mon Sep 17 00:00:00 2001 From: Todd Previte Date: Wed, 15 Apr 2015 08:38:41 -0700 Subject: [PATCH] drm/i915: Add a delay in Displayport AUX transactions for compliance testing 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. Also, the check for DP_AUX_CH_CTL_TIME_OUT_ERROR has been moved out into a separate case. This case just continues with the next iteration of the loop as the HW has already waited the required amount of time. V2: - Changed udelay() to usleep_range() V3: - Removed extraneous check for timeout - Updated comment to reflect this change V4: - Reformatted a comment V5: - Added separate check for HW timeout on AUX transactions. A message is logged upon detection of this case. V6: - Add continue statement to HW timeout detect case - Remove the log message indicating a timeout has been detected (review feedback) V7: - Updated the commit message to remove verbage about the HW timeout case that is no longer valid. Signed-off-by: Todd Previte Reviewed-by: Paulo Zanoni Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_dp.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c index 371d1e6129e5..ae4baf96bb00 100644 --- a/drivers/gpu/drm/i915/intel_dp.c +++ b/drivers/gpu/drm/i915/intel_dp.c @@ -874,9 +874,18 @@ intel_dp_aux_ch(struct intel_dp *intel_dp, DP_AUX_CH_CTL_TIME_OUT_ERROR | DP_AUX_CH_CTL_RECEIVE_ERROR); - if (status & (DP_AUX_CH_CTL_TIME_OUT_ERROR | - DP_AUX_CH_CTL_RECEIVE_ERROR)) + if (status & DP_AUX_CH_CTL_TIME_OUT_ERROR) continue; + + /* DP CTS 1.2 Core Rev 1.1, 4.2.1.1 & 4.2.1.2 + * 400us delay required for errors and timeouts + * Timeout errors from the HW already meet this + * requirement so skip to next iteration + */ + if (status & DP_AUX_CH_CTL_RECEIVE_ERROR) { + usleep_range(400, 500); + continue; + } if (status & DP_AUX_CH_CTL_DONE) break; } -- 2.20.1