Re: [Intel-gfx] [PATCH 2/2] drm/i915/dp: use new link training delay helpers

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Oct 12, 2021 at 05:43:21PM +0300, Jani Nikula wrote:
> Use the new link training delay helpers, fixing the delays for
> 128b/132b.
> 
> For existing 8b/10b functionality, this will cause additional 1-byte
> DPCD reads for LTTPR delays instead of using the cached values. It's
> just too complicated to combine generic helpers with local caching in a
> sensible way.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>

I was just pondering if the extra DPCD reads might cause some grief for
some compliance test stuff. But I guess if that happens we could just
read them all at the very start of link training, or something.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  .../drm/i915/display/intel_dp_link_training.c | 38 +++++++------------
>  1 file changed, 13 insertions(+), 25 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 85676c953e0a..a72f2dc93718 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -683,15 +683,6 @@ intel_dp_prepare_link_train(struct intel_dp *intel_dp,
>  	return true;
>  }
>  
> -static void intel_dp_link_training_clock_recovery_delay(struct intel_dp *intel_dp,
> -							enum drm_dp_phy dp_phy)
> -{
> -	if (dp_phy == DP_PHY_DPRX)
> -		drm_dp_link_train_clock_recovery_delay(&intel_dp->aux, intel_dp->dpcd);
> -	else
> -		drm_dp_lttpr_link_train_clock_recovery_delay();
> -}
> -
>  static bool intel_dp_adjust_request_changed(const struct intel_crtc_state *crtc_state,
>  					    const u8 old_link_status[DP_LINK_STATUS_SIZE],
>  					    const u8 new_link_status[DP_LINK_STATUS_SIZE])
> @@ -750,6 +741,11 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp,
>  	u8 link_status[DP_LINK_STATUS_SIZE];
>  	bool max_vswing_reached = false;
>  	char phy_name[10];
> +	int delay_us;
> +
> +	delay_us = drm_dp_read_clock_recovery_delay(&intel_dp->aux,
> +						    intel_dp->dpcd, dp_phy,
> +						    intel_dp_is_uhbr(crtc_state));
>  
>  	intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name));
>  
> @@ -777,7 +773,7 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp,
>  
>  	voltage_tries = 1;
>  	for (cr_tries = 0; cr_tries < max_cr_tries; ++cr_tries) {
> -		intel_dp_link_training_clock_recovery_delay(intel_dp, dp_phy);
> +		usleep_range(delay_us, 2 * delay_us);
>  
>  		if (drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, dp_phy,
>  						     link_status) < 0) {
> @@ -895,19 +891,6 @@ static u32 intel_dp_training_pattern(struct intel_dp *intel_dp,
>  	return DP_TRAINING_PATTERN_2;
>  }
>  
> -static void
> -intel_dp_link_training_channel_equalization_delay(struct intel_dp *intel_dp,
> -						  enum drm_dp_phy dp_phy)
> -{
> -	if (dp_phy == DP_PHY_DPRX) {
> -		drm_dp_link_train_channel_eq_delay(&intel_dp->aux, intel_dp->dpcd);
> -	} else {
> -		const u8 *phy_caps = intel_dp_lttpr_phy_caps(intel_dp, dp_phy);
> -
> -		drm_dp_lttpr_link_train_channel_eq_delay(&intel_dp->aux, phy_caps);
> -	}
> -}
> -
>  /*
>   * Perform the link training channel equalization phase on the given DP PHY
>   * using one of training pattern 2, 3 or 4 depending on the source and
> @@ -925,6 +908,11 @@ intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp,
>  	u8 link_status[DP_LINK_STATUS_SIZE];
>  	bool channel_eq = false;
>  	char phy_name[10];
> +	int delay_us;
> +
> +	delay_us = drm_dp_read_channel_eq_delay(&intel_dp->aux,
> +						intel_dp->dpcd, dp_phy,
> +						intel_dp_is_uhbr(crtc_state));
>  
>  	intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name));
>  
> @@ -944,8 +932,8 @@ intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp,
>  	}
>  
>  	for (tries = 0; tries < 5; tries++) {
> -		intel_dp_link_training_channel_equalization_delay(intel_dp,
> -								  dp_phy);
> +		usleep_range(delay_us, 2 * delay_us);
> +
>  		if (drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, dp_phy,
>  						     link_status) < 0) {
>  			drm_err(&i915->drm,
> -- 
> 2.30.2

-- 
Ville Syrjälä
Intel