drm/msm/dp: Prepare for link training per-segment for LTTPRs

Per-segment link training requires knowing the number of LTTPRs
(if any) present. Store the count during LTTPRs' initialization.

Fixes: 72d0af4 ("drm/msm/dp: Add support for LTTPR handling")
Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Aleksandrs Vinarskis <alex.vinarskis@gmail.com>
Tested-by: Jessica Zhang <quic_jesszhan@quicinc.com> # SA8775P
Tested-by: Johan Hovold <johan+linaro@kernel.org>
Tested-by: Rob Clark <robdclark@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/652306/
Link: https://lore.kernel.org/r/20250507230113.14270-4-alex.vinarskis@gmail.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

Author: alexVinarskis

drivers/gpu/drm/msm/dp/dp_display.c

@@ -360,16 +360,21 @@ static int msm_dp_display_send_hpd_notification(struct msm_dp_display_private *d
 	return 0;
 }
 
-static void msm_dp_display_lttpr_init(struct msm_dp_display_private *dp, u8 *dpcd)
+static int msm_dp_display_lttpr_init(struct msm_dp_display_private *dp, u8 *dpcd)
 {
-	int rc;
+	int rc, lttpr_count;
 
 	if (drm_dp_read_lttpr_common_caps(dp->aux, dpcd, dp->link->lttpr_common_caps))
-		return;
+		return 0;
 
-	rc = drm_dp_lttpr_init(dp->aux, drm_dp_lttpr_count(dp->link->lttpr_common_caps));
-	if (rc)
+	lttpr_count = drm_dp_lttpr_count(dp->link->lttpr_common_caps);
+	rc = drm_dp_lttpr_init(dp->aux, lttpr_count);
+	if (rc) {
 		DRM_ERROR("failed to set LTTPRs transparency mode, rc=%d\n", rc);
+		return 0;
+	}
+
+	return lttpr_count;
 }
 
 static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
@@ -383,7 +388,7 @@ static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
 	if (rc)
 		goto end;
 
-	msm_dp_display_lttpr_init(dp, dpcd);
+	dp->link->lttpr_count = msm_dp_display_lttpr_init(dp, dpcd);
 
 	rc = msm_dp_panel_read_sink_caps(dp->panel, connector);
 	if (rc)

drivers/gpu/drm/msm/dp/dp_link.h

@@ -62,6 +62,7 @@ struct msm_dp_link_phy_params {
 
 struct msm_dp_link {
 	u8 lttpr_common_caps[DP_LTTPR_COMMON_CAP_SIZE];
+	int lttpr_count;
 
 	u32 sink_request;
 	u32 test_response;