drm/i915: Fix modesetting in case of unexpected AUX timeouts
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: 7dffbded ("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.deak@intel.com (cherry picked from commit e42e7e58) Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com> [adjusted Fixes: tag]
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