On Fri, 01 Jul 2022, Arun R Murthy <arun.r.murthy@xxxxxxxxx> wrote: > On linktraining error/timeout before retry need to wait for 400usec as > per the DP CTS spec1.2 > > The patch with commit 74ebf294a1dd ("drm/i915: Add a delay in Displayport > AUX transactions for compliance testing") > removes this delay mentioning the hardware already meets this requirement, > but as per the spec the delay mentioned in the spec specifies how long to > wait for the receiver response before timeout. So the delay here to wait > for timeout and not a delay after timeout. The DP spec specifies a delay > after timeout and hence adding this delay. > > v2: fixed checkpatch warning and error > v3: used proper indentation > > Signed-off-by: Arun R Murthy <arun.r.murthy@xxxxxxxxx> Based on the description alone, Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx> but would be good if you could get someone to double check the details against bspec and CTS. > --- > drivers/gpu/drm/i915/display/intel_dp_aux.c | 8 ++------ > 1 file changed, 2 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c > index 2bc119374555..722c9f210690 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c > @@ -286,13 +286,9 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp, > /* > * 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_TIME_OUT_ERROR) > - continue; > - > - if (status & DP_AUX_CH_CTL_RECEIVE_ERROR) { > + if (status & (DP_AUX_CH_CTL_RECEIVE_ERROR | > + DP_AUX_CH_CTL_TIME_OUT_ERROR)) { > usleep_range(400, 500); > continue; > } -- Jani Nikula, Intel Open Source Graphics Center