Merge tag 'drm-intel-next-fixes-2024-07-18' of...

Merge tag 'drm-intel-next-fixes-2024-07-18' of https://gitlab.freedesktop.org/drm/i915/kernel into drm-next

- Reset intel_dp->link_trained before retraining the link [dp] (Imre Deak)
- Don't switch the LTTPR mode on an active link [dp] (Imre Deak)
Signed-off-by: Dave Airlie <airlied@redhat.com>
From: Tvrtko Ursulin <tursulin@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ZpjgtowjpUZoHvrl@linux

drivers/gpu/drm/i915/display/intel_dp.c

@@ -5314,6 +5314,8 @@ static int intel_dp_retrain_link(struct intel_encoder *encoder,
 		const struct intel_crtc_state *crtc_state =
 			to_intel_crtc_state(crtc->base.state);
 
+		intel_dp->link_trained = false;
+
 		intel_dp_check_frl_training(intel_dp);
 		intel_dp_pcon_dsc_configure(intel_dp, crtc_state);
 		intel_dp_start_link_train(NULL, intel_dp, crtc_state);

drivers/gpu/drm/i915/display/intel_dp_link_training.c

@@ -117,10 +117,24 @@ intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable)
 	return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) == 1;
 }
 
-static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+static bool intel_dp_lttpr_transparent_mode_enabled(struct intel_dp *intel_dp)
+{
+	return intel_dp->lttpr_common_caps[DP_PHY_REPEATER_MODE -
+					   DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV] ==
+		DP_PHY_REPEATER_MODE_TRANSPARENT;
+}
+
+/*
+ * Read the LTTPR common capabilities and switch the LTTPR PHYs to
+ * non-transparent mode if this is supported. Preserve the
+ * transparent/non-transparent mode on an active link.
+ *
+ * Return the number of detected LTTPRs in non-transparent mode or 0 if the
+ * LTTPRs are in transparent mode or the detection failed.
+ */
+static int intel_dp_init_lttpr_phys(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 {
 	int lttpr_count;
-	int i;
 
 	if (!intel_dp_read_lttpr_common_caps(intel_dp, dpcd))
 		return 0;
@@ -134,6 +148,19 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEI
 	if (lttpr_count == 0)
 		return 0;
 
+	/*
+	 * Don't change the mode on an active link, to prevent a loss of link
+	 * synchronization. See DP Standard v2.0 3.6.7. about the LTTPR
+	 * resetting its internal state when the mode is changed from
+	 * non-transparent to transparent.
+	 */
+	if (intel_dp->link_trained) {
+		if (lttpr_count < 0 || intel_dp_lttpr_transparent_mode_enabled(intel_dp))
+			goto out_reset_lttpr_count;
+
+		return lttpr_count;
+	}
+
 	/*
 	 * See DP Standard v2.0 3.6.6.1. about the explicit disabling of
 	 * non-transparent mode and the disable->enable non-transparent mode
@@ -154,11 +181,25 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEI
 		       "Switching to LTTPR non-transparent LT mode failed, fall-back to transparent mode\n");
 
 		intel_dp_set_lttpr_transparent_mode(intel_dp, true);
-		intel_dp_reset_lttpr_count(intel_dp);
 
-		return 0;
+		goto out_reset_lttpr_count;
 	}
 
+	return lttpr_count;
+
+out_reset_lttpr_count:
+	intel_dp_reset_lttpr_count(intel_dp);
+
+	return 0;
+}
+
+static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	int lttpr_count;
+	int i;
+
+	lttpr_count = intel_dp_init_lttpr_phys(intel_dp, dpcd);
+
 	for (i = 0; i < lttpr_count; i++)
 		intel_dp_read_lttpr_phy_caps(intel_dp, dpcd, DP_PHY_LTTPR(i));
 
@@ -1482,10 +1523,10 @@ void intel_dp_start_link_train(struct intel_atomic_state *state,
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	struct intel_encoder *encoder = &dig_port->base;
 	bool passed;
-
 	/*
-	 * TODO: Reiniting LTTPRs here won't be needed once proper connector
-	 * HW state readout is added.
+	 * Reinit the LTTPRs here to ensure that they are switched to
+	 * non-transparent mode. During an earlier LTTPR detection this
+	 * could've been prevented by an active link.
 	 */
 	int lttpr_count = intel_dp_init_lttpr_and_dprx_caps(intel_dp);