[Intel-gfx] [PATCH v2] drm/i915/edp: Do not do link training fallback or prune modes on EDP

[Imre Deak]

On Thu, Oct 12, 2017 at 12:13:38PM -0700, Manasi Navare wrote:
> In case of eDP because the panel has a fixed mode, the link rate
> and lane count at which it is trained corresponds to the link BW
> required to support the native resolution of the panel. In case of
> panles with lower resolutions where fewer lanes are hooked up internally,
> that number is reflected in the MAX_LANE_COUNT DPCD register of the panel.
> So it is pointless to fallback to lower link rate/lane count in case
> of link training failure on eDP connector since the lower link BW
> will not support the native resolution of the panel and we cannot
> prune the preferred mode on the eDP connector.
> 
> In case of Link training failure on the eDP panel, something is wrong
> in the HW internally and hence driver errors out with a loud
> and clear DRM_ERROR message.
> 
> v2:
> * Fix the DEBUG_ERROR and add {} in else (Ville Syrjala)
> 
> Cc: Clinton Taylor <clinton.a.taylor at intel.com>
> Cc: Jim Bride <jim.bride at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: Dave Airlie <airlied at redhat.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> Reviewed-by: Ville Syrjala <ville.syrjala at linux.intel.com>

This fell through the cracks, looks like it partially fixes
https://bugs.freedesktop.org/show_bug.cgi?id=103369

Why link training fails there is not clear.

> ---
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 05907fa..cf8fef8 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -328,14 +328,22 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
>  	return;
>  
>   failure_handling:
> -	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
> -		      intel_connector->base.base.id,
> -		      intel_connector->base.name,
> -		      intel_dp->link_rate, intel_dp->lane_count);
> -	if (!intel_dp_get_link_train_fallback_values(intel_dp,
> -						     intel_dp->link_rate,
> -						     intel_dp->lane_count))
> -		/* Schedule a Hotplug Uevent to userspace to start modeset */
> -		schedule_work(&intel_connector->modeset_retry_work);
> +	/* Dont fallback and prune modes if its eDP */
> +	if (!intel_dp_is_edp(intel_dp)) {
> +		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
> +			      intel_connector->base.base.id,
> +			      intel_connector->base.name,
> +			      intel_dp->link_rate, intel_dp->lane_count);
> +		if (!intel_dp_get_link_train_fallback_values(intel_dp,
> +							     intel_dp->link_rate,
> +							     intel_dp->lane_count))
> +			/* Schedule a Hotplug Uevent to userspace to start modeset */
> +			schedule_work(&intel_connector->modeset_retry_work);
> +	} else {
> +		DRM_ERROR("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
> +			  intel_connector->base.base.id,
> +			  intel_connector->base.name,
> +			  intel_dp->link_rate, intel_dp->lane_count);
> +	}
>  	return;
>  }
> -- 
> 2.1.4
> 
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