The patch below does not apply to the 5.11-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d2b9935d65dab6e92beb33c150c1a6ded14ab670 Mon Sep 17 00:00:00 2001

From: Imre Deak imre.deak@intel.com Date: Tue, 13 Apr 2021 02:24:12 +0300 Subject: [PATCH] drm/i915: Fix modesetting in case of unexpected AUX timeouts MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

In case AUX failures happen unexpectedly during a modeset, the driver should still complete the modeset. In particular the driver should perform the link training sequence steps even in case of an AUX failure, as this sequence also includes port initialization steps. Not doing that can leave the port/pipe in a broken state and lead for instance to a flip done timeout.

Fix this by continuing with link training (in a no-LTTPR mode) if the DPRX DPCD readout failed for some reason at the beginning of link training. After a successful connector detection we already have the DPCD read out and cached, so the failed repeated read for it should not cause a problem. Note that a partial AUX read could in theory partly overwrite the cached DPCD (and return error) but this overwrite should not happen if the returned values are corrupted (due to a timeout or some other IO error).

Kudos to Ville to root cause the problem.

Fixes: 7dffbdedb96a ("drm/i915: Disable LTTPR support when the DPCD rev < 1.4") References: https://gitlab.freedesktop.org/drm/intel/-/issues/3308 Cc: stable@vger.kernel.org # 5.11 Cc: Ville Syrjälä ville.syrjala@linux.intel.com Signed-off-by: Imre Deak imre.deak@intel.com Reviewed-by: Ville Syrjälä ville.syrjala@linux.intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20210412232413.2755054-1-imre.... (cherry picked from commit e42e7e585984b85b0fb9dd1fefc85ee4800ca629) Signed-off-by: Rodrigo Vivi rodrigo.vivi@intel.com [adjusted Fixes: tag]

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 be6ac0dd846e..2ed309534e97 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c @@ -848,7 +848,8 @@ void intel_dp_start_link_train(struct intel_dp *intel_dp, int lttpr_count = intel_dp_init_lttpr_and_dprx_caps(intel_dp);

if (lttpr_count < 0) - return; + /* Still continue with enabling the port and link training. */ + lttpr_count = 0;

if (!intel_dp_link_train_all_phys(intel_dp, crtc_state, lttpr_count)) intel_dp_schedule_fallback_link_training(intel_dp, crtc_state);