drm/i915: Disable LTTPR support when the LTTPR rev < 1.4

By the specification the 0xF0000 - 0xF02FF range is only valid if the
LTTPR revision at 0xF0000 is at least 1.4. Disable the LTTPR support
otherwise.

Fixes: 7b2a4ab8b0ef ("drm/i915: Switch to LTTPR transparent mode link training")
Cc: <stable@vger.kernel.org> # v5.11
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/20210317184901.4029798-4-imre.deak@intel.com
(cherry picked from commit 1663ad4936e0679443a315fe342f99636a2420dd)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

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 c10e81a..be6ac0d 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -99,17 +99,23 @@ static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp)
                return false;
 
        if (drm_dp_read_lttpr_common_caps(&intel_dp->aux,
-                                         intel_dp->lttpr_common_caps) < 0) {
-               intel_dp_reset_lttpr_common_caps(intel_dp);
-               return false;
-       }
+                                         intel_dp->lttpr_common_caps) < 0)
+               goto reset_caps;
 
        drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
                    "LTTPR common capabilities: %*ph\n",
                    (int)sizeof(intel_dp->lttpr_common_caps),
                    intel_dp->lttpr_common_caps);
 
+       /* The minimum value of LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV is 1.4 */
+       if (intel_dp->lttpr_common_caps[0] < 0x14)
+               goto reset_caps;
+
        return true;
+
+reset_caps:
+       intel_dp_reset_lttpr_common_caps(intel_dp);
+       return false;
 }
 
 static bool