[Intel-gfx] [PATCH v1] drm/i915: Minor link training logic fixes for dp_mst

[Imre Deak]

On Wed, May 27, 2020 at 11:00:22PM +0300, Stanislav Lisovskiy wrote:
> First of all *_needs_link_retraining function should return
> false is link_train is set to true but not false.
> 
> Also if we detect channel eq problem when checking mst status
> we simply bail out, without setting link_train to false again,
> which might end up in a situation that we don't do link retraining
> when needed.
> 
> There were some issues, when we had several problems with dp mst
> and at the same time the log was floode by messages about
> "channel eq not ok, need retraining" however the actual training
> seems to be never done.
> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 1768731678a1..9288dc1f8914 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5627,6 +5627,7 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  			drm_dbg_kms(&i915->drm,
>  				    "channel EQ not ok, retraining\n");
>  			need_retrain = true;
> +			intel_dp->link_trained = false;
>  		}
>  
>  		drm_dbg_kms(&i915->drm, "got esi %3ph\n", esi);
> @@ -5654,7 +5655,7 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
>  {
>  	u8 link_status[DP_LINK_STATUS_SIZE];
>  
> -	if (!intel_dp->link_trained)
> +	if (intel_dp->link_trained)

intel_dp->link_trained is set when we trained the link during a modeset,
it doesn't mean that the link status is good, as you seem to interpret
it. With this change I don't see how we would retrain the link when this
is called from intel_dp_short_pulse(). Could you describe more the
failing scenario?

>  		return false;
>  
>  	/*
> -- 
> 2.24.1.485.gad05a3d8e5
>