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Commit 04144445 authored by Manasi Navare's avatar Manasi Navare Committed by Rodrigo Vivi
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drm/i915/dp: Link train Fallback on eDP only if fallback link BW can fit panel's native mode 

This patch fixes the original commit c0cfb10d ("drm/i915/edp:
Do not do link training fallback or prune modes on EDP") that causes
a blank screen in case of certain eDP panels (Eg: seen on Dell XPS13 9350)
where first link training fails and a retraining is required by falling
back to lower link rate/lane count.
In case of some panels they advertise higher link rate/lane count
than whats required for supporting the panel's native mode.
But we always link train at highest link rate/lane count for eDP
and if that fails we can still fallback to lower link rate/lane count
as long as the fallback link BW still fits the native mode to avoid
pruning the panel's native mode yet retraining at fallback values
to recover from a blank screen.

v3:
* Add const for fixed_mode (Ville)
v2:
* Send uevent if link failure on eDP unconditionally

Fixes: c0cfb10d ("drm/i915/edp: Do not do link training fallback or prune modes on EDP")
Cc: Clinton Taylor <clinton.a.taylor@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: <stable@vger.kernel.org> # v4.17+
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107489
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105338


Signed-off-by: default avatarManasi Navare <manasi.d.navare@intel.com>
Tested-by: default avatarAlexander Wilson <alexander.wilson@ncf.edu>
Reviewed-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181009212804.702-1-manasi.d.navare@intel.com


(cherry picked from commit 1e712535)
Signed-off-by: default avatarRodrigo Vivi <rodrigo.vivi@intel.com>
parent 4bbf0d47

drivers/gpu/drm/i915/intel_dp.c

+30 −0
Original line number Diff line number Diff line
@@ -557,6 +557,22 @@ static bool intel_dp_link_params_valid(struct intel_dp *intel_dp, int link_rate, 
	return true;

}



static bool intel_dp_can_link_train_fallback_for_edp(struct intel_dp *intel_dp,

						     int link_rate,

						     uint8_t lane_count)

{

	const struct drm_display_mode *fixed_mode =

		intel_dp->attached_connector->panel.fixed_mode;

	int mode_rate, max_rate;



	mode_rate = intel_dp_link_required(fixed_mode->clock, 18);

	max_rate = intel_dp_max_data_rate(link_rate, lane_count);

	if (mode_rate > max_rate)

		return false;



	return true;

}



int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,

					    int link_rate, uint8_t lane_count)

{
@@ -566,9 +582,23 @@ int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp, 
				    intel_dp->num_common_rates,

				    link_rate);

	if (index > 0) {

		if (intel_dp_is_edp(intel_dp) &&

		    !intel_dp_can_link_train_fallback_for_edp(intel_dp,

							      intel_dp->common_rates[index - 1],

							      lane_count)) {

			DRM_DEBUG_KMS("Retrying Link training for eDP with same parameters\n");

			return 0;

		}

		intel_dp->max_link_rate = intel_dp->common_rates[index - 1];

		intel_dp->max_link_lane_count = lane_count;

	} else if (lane_count > 1) {

		if (intel_dp_is_edp(intel_dp) &&

		    !intel_dp_can_link_train_fallback_for_edp(intel_dp,

							      intel_dp_max_common_rate(intel_dp),

							      lane_count >> 1)) {

			DRM_DEBUG_KMS("Retrying Link training for eDP with same parameters\n");

			return 0;

		}

		intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);

		intel_dp->max_link_lane_count = lane_count >> 1;

	} else {

drivers/gpu/drm/i915/intel_dp_link_training.c

+9 −17
Original line number Diff line number Diff line
@@ -367,8 +367,6 @@ intel_dp_start_link_train(struct intel_dp *intel_dp) 
	return;



 failure_handling:

	/* 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,
@@ -378,11 +376,5 @@ intel_dp_start_link_train(struct intel_dp *intel_dp) 
						     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;

}