[Intel-gfx] [PATCH] drm/i915: WARN if max vswing/pre-emphasis violates the DP spec

[Souza, Jose]

On Thu, 2020-07-09 at 17:58 +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> According to the DP spec a DPTX must support vswing/pre-emphasis
> up to and including level 2. Level 3 is optional (actually DP 1.4a
> seems to make even level 3 mandatory for HBR2/3, while leaving it
> optional for RBR/HBR1).
> 
> WARN if out encoders' .voltage_max()/.preemph_max() return
> an illegal value.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_link_training.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> 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 2493142a70e9..a23ed7290843 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -52,6 +52,7 @@ static u8 dp_voltage_max(u8 preemph)
>  void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
>  			       const u8 link_status[DP_LINK_STATUS_SIZE])
>  {
> +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>  	u8 v = 0;
>  	u8 p = 0;
>  	int lane;
> @@ -64,12 +65,20 @@ void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
>  	}
>  
>  	preemph_max = intel_dp->preemph_max(intel_dp);
> +	drm_WARN_ON_ONCE(&i915->drm,
> +			 preemph_max != DP_TRAIN_PRE_EMPH_LEVEL_2 &&
> +			 preemph_max != DP_TRAIN_PRE_EMPH_LEVEL_3);

Okay matches but I guess the preemph_max function should receive as parameter the voltage level to it return the max preemph of that voltage level,
no?

> +
>  	if (p >= preemph_max)
>  		p = preemph_max | DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;
>  
>  	v = min(v, dp_voltage_max(p));
>  
>  	voltage_max = intel_dp->voltage_max(intel_dp);
> +	drm_WARN_ON_ONCE(&i915->drm,
> +			 voltage_max != DP_TRAIN_VOLTAGE_SWING_LEVEL_2 &&
> +			 voltage_max != DP_TRAIN_VOLTAGE_SWING_LEVEL_3);
> +
>  	if (v >= voltage_max)
>  		v = voltage_max | DP_TRAIN_MAX_SWING_REACHED;
>