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Subject[PATCH 4.18 155/171] drm/i915/dp: Link train Fallback on eDP only if fallback link BW can fit panels native mode
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Manasi Navare <manasi.d.navare@intel.com>

commit 041444458835d7fb2c9f042598bfe16bf375b15d upstream.

This patch fixes the original commit c0cfb10d9e1de49 ("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: c0cfb10d9e1d ("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: Manasi Navare <manasi.d.navare@intel.com>
Tested-by: Alexander Wilson <alexander.wilson@ncf.edu>
Reviewed-by: Ville 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 1e712535c51ab025ebc776d4405683d81521996d)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/i915/intel_dp.c | 30 ++++++++++++++++++++++++++
drivers/gpu/drm/i915/intel_dp_link_training.c | 26 +++++++---------------
2 files changed, 39 insertions(+), 17 deletions(-)

--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -387,6 +387,22 @@ static bool intel_dp_link_params_valid(s
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)
{
@@ -396,9 +412,23 @@ int intel_dp_get_link_train_fallback_val
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 {
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -335,22 +335,14 @@ intel_dp_start_link_train(struct intel_d
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,
- 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);
- }
+ 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);
return;
}

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