drm/i915/dp: Use max params for panels < eDP 1.4

Users reported that after commit 7a1aa17b7f3c ("drm/i915: Try to use
fast+narrow link on eDP again and fall back to the old max strategy on
failure"), the screen starts to have wobbly effect.

Commit 4abac14488ee ("drm/i915/dp: Use slow and wide link training for
everything") doesn't help either, that means the affected eDP 1.2 panels
only work with max params.

So use max params for panels < eDP 1.4 as Windows does to solve the
issue.

v3:
 - Do the eDP rev check in intel_edp_init_dpcd()

v2:
 - Check eDP 1.4 instead of DPCD 1.1 to apply max params

Cc: stable@vger.kernel.org
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3714
Fixes: 7a1aa17b7f3c ("drm/i915: Try to use fast+narrow link on eDP again and fall back to the old max strategy on failure")
Fixes: 4abac14488ee ("drm/i915/dp: Use slow and wide link training for everything")
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210820075301.693099-1-kai.heng.feng@canonical.com
(cherry picked from commit d7f213c131adf0bec8b731553eb82990cdac265d)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 04175f359fd6857c4941095cf0e6489cd9bb74bc..abe3d61b624329c9a993aa3a763e5c39bce67588 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2445,11 +2445,14 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
         */
        if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_DPCD_REV,
                             intel_dp->edp_dpcd, sizeof(intel_dp->edp_dpcd)) ==
-                            sizeof(intel_dp->edp_dpcd))
+                            sizeof(intel_dp->edp_dpcd)) {
                drm_dbg_kms(&dev_priv->drm, "eDP DPCD: %*ph\n",
                            (int)sizeof(intel_dp->edp_dpcd),
                            intel_dp->edp_dpcd);
 
+               intel_dp->use_max_params = intel_dp->edp_dpcd[0] < DP_EDP_14;
+       }
+
        /*
         * This has to be called after intel_dp->edp_dpcd is filled, PSR checks
         * for SET_POWER_CAPABLE bit in intel_dp->edp_dpcd[1]