[Intel-gfx] [PATCH v2 2/2] drm/i915/dp: Add workaround for spurious AUX timeouts/hotplugs on LTTPR links

[Imre Deak]

Some ADLP DP link configuration at least with multiple LTTPRs expects
the first DPCD access during the LTTPR/DPCD detection after hotplug to
be a read from the LTTPR range starting with
DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV. The side effect of
this read is to put each LTTPR into the LTTPR transparent or LTTPR
non-transparent mode.

The lack of the above read may leave some of the LTTPRs in non-LTTPR
mode, while other LTTPRs in LTTPR transparent or LTTPR non-transparent
mode (for instance LTTPRs after system suspend/resume that kept their
mode from before suspend). Due to the different AUX timeouts the
different modes imply, the DPCD access from a non-LTTPR range will
timeout and lead to an LTTPR generated hotplug towards the source (which
the LTTPR firmware uses to account for buggy TypeC adapters with a long
wake-up delay).

To avoid the above AUX timeout and subsequent hotplug interrupt, make
sure that the first DPCD access during detection is a read from an
LTTPR register.

VLK: SYSCROS-72939

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 .../drm/i915/display/intel_dp_link_training.c | 25 +++++++++++--------
 1 file changed, 14 insertions(+), 11 deletions(-)

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 26f9e2b748e40..8f4f3b6637c81 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -82,19 +82,8 @@ static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp,
 					    const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 {
 	struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
-	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
 	int ret;
 
-	if (intel_dp_is_edp(intel_dp))
-		return false;
-
-	/*
-	 * Detecting LTTPRs must be avoided on platforms with an AUX timeout
-	 * period < 3.2ms. (see DP Standard v2.0, 2.11.2, 3.6.6.1).
-	 */
-	if (DISPLAY_VER(i915) < 10 || IS_GEMINILAKE(i915))
-		return false;
-
 	ret = drm_dp_read_lttpr_common_caps(&intel_dp->aux, dpcd,
 					    intel_dp->lttpr_common_caps);
 	if (ret < 0)
@@ -197,12 +186,26 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEI
  */
 int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp)
 {
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	/*
+	 * Detecting LTTPRs must be avoided on platforms with an AUX timeout
+	 * period < 3.2ms. (see DP Standard v2.0, 2.11.2, 3.6.6.1).
+	 */
+	bool init_lttpr = !intel_dp_is_edp(intel_dp) &&
+			  (DISPLAY_VER(i915) >= 10 && !IS_GEMINILAKE(i915));
 	u8 dpcd[DP_RECEIVER_CAP_SIZE];
 	int lttpr_count;
 
+	if (init_lttpr &&
+	    drm_dp_dpcd_probe(&intel_dp->aux, DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV))
+		return -EIO;
+
 	if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd))
 		return -EIO;
 
+	if (!init_lttpr)
+		return 0;
+
 	lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd);
 
 	/*
-- 
2.30.2