Re: [Intel-gfx] [PATCH v4 1/2] drm/i915/dp: abstract intel_dp_lane_max_vswing_reached()

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

On Thu, Oct 07, 2021 at 04:39:07PM +0300, Jani Nikula wrote:
> Add per-lane abstraction for max vswing reached to make follow-up
> cleaner, as this one reverses the conditions.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  .../drm/i915/display/intel_dp_link_training.c | 42 +++++++++++--------
>  1 file changed, 25 insertions(+), 17 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 1a943ae38a6b..d239d72bfcf2 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -515,29 +515,37 @@ intel_dp_update_link_train(struct intel_dp *intel_dp,
>  	return ret == crtc_state->lane_count;
>  }
>  
> +/*
> + * FIXME: The DP spec is very confusing here, also the Link CTS spec seems to
> + * have self contradicting tests around this area.
> + *
> + * In lieu of better ideas let's just stop when we've reached the max supported
> + * vswing with its max pre-emphasis, which is either 2+1 or 3+0 depending on
> + * whether vswing level 3 is supported or not.
> + */
> +static bool intel_dp_lane_max_vswing_reached(u8 train_set_lane)
> +{
> +	u8 v = (train_set_lane & DP_TRAIN_VOLTAGE_SWING_MASK) >>
> +		DP_TRAIN_VOLTAGE_SWING_SHIFT;
> +	u8 p = (train_set_lane & DP_TRAIN_PRE_EMPHASIS_MASK) >>
> +		DP_TRAIN_PRE_EMPHASIS_SHIFT;
> +
> +	if (train_set_lane & DP_TRAIN_MAX_SWING_REACHED)
> +		return true;
> +
> +	if (v + p == 3)
> +		return true;

We want both to be true at the same time.

> +
> +	return false;
> +}
> +
>  static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp,
>  					     const struct intel_crtc_state *crtc_state)
>  {
>  	int lane;
>  
> -	/*
> -	 * FIXME: The DP spec is very confusing here, also the Link CTS
> -	 * spec seems to have self contradicting tests around this area.
> -	 *
> -	 * In lieu of better ideas let's just stop when we've reached the
> -	 * max supported vswing with its max pre-emphasis, which is either
> -	 * 2+1 or 3+0 depending on whether vswing level 3 is supported or not.
> -	 */
>  	for (lane = 0; lane < crtc_state->lane_count; lane++) {
> -		u8 v = (intel_dp->train_set[lane] & DP_TRAIN_VOLTAGE_SWING_MASK) >>
> -			DP_TRAIN_VOLTAGE_SWING_SHIFT;
> -		u8 p = (intel_dp->train_set[lane] & DP_TRAIN_PRE_EMPHASIS_MASK) >>
> -			DP_TRAIN_PRE_EMPHASIS_SHIFT;
> -
> -		if ((intel_dp->train_set[lane] & DP_TRAIN_MAX_SWING_REACHED) == 0)
> -			return false;
> -
> -		if (v + p != 3)
> +		if (!intel_dp_lane_max_vswing_reached(intel_dp->train_set[lane]))
>  			return false;
>  	}
>  
> -- 
> 2.30.2

-- 
Ville Syrjälä
Intel