On Thu, 12 Sep 2024, Arun R Murthy <arun.r.murthy@xxxxxxxxx> wrote:
> DP Source should be reading AUX_RD interval after we get adjusted
> TX_FFE_PRESET_VALUE from the DP Sink. (before actually adjusting
> in DP Source)
I don't think that's correct. See below.
> Signed-off-by: Srikanth V NagaVenkata <nagavenkata.srikanth.v@xxxxxxxxx>
> Signed-off-by: Arun R Murthy <arun.r.murthy@xxxxxxxxx>
> ---
> .../gpu/drm/i915/display/intel_dp_link_training.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> index f41b69840ad9..ca179bed46ad 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -1419,12 +1419,6 @@ intel_dp_128b132b_lane_eq(struct intel_dp *intel_dp,
> for (try = 0; try < max_tries; try++) {
> fsleep(delay_us);
>
> - /*
> - * The delay may get updated. The transmitter shall read the
> - * delay before link status during link training.
> - */
> - delay_us = drm_dp_128b132b_read_aux_rd_interval(&intel_dp->aux);
> -
> if (drm_dp_dpcd_read_link_status(&intel_dp->aux, link_status) < 0) {
> lt_err(intel_dp, DP_PHY_DPRX, "Failed to read link status\n");
> return false;
> @@ -1457,6 +1451,12 @@ intel_dp_128b132b_lane_eq(struct intel_dp *intel_dp,
> lt_err(intel_dp, DP_PHY_DPRX, "Failed to update TX FFE settings\n");
> return false;
> }
> +
> + /*
> + * The delay may get updated. The transmitter shall read the
> + * delay before link status during link training.
> + */
> + delay_us = drm_dp_128b132b_read_aux_rd_interval(&intel_dp->aux);
This is clearly an improvement, but Figure 3-52 of DP 2.1a has "Read
AUX_RD_INTERVAL value" before "Adjust requested the TX_FFE_PRESET_VALUE
by a DPRX/LTTPR_UFP setting". Yes, in the same box in the flow chart,
but before.
Sticking with the spec, the read should be placed above this comment:
/* Update signal levels and training set as requested. */
Be sure to reference the spec in the commit message.
BR,
Jani.
> }
>
> if (try == max_tries) {
--
Jani Nikula, Intel
