[PATCH v4] drm/msm/dp: allow eDP sinks without DP_SINK_COUNT

[Vivek Kumar <vk092kumar@gmail.com>]

Some eDP sinks, especially fixed-format eDP-to-HDMI bridge chips with
no downstream AUX-capable panel behind them, do not report a non-zero
DP_SINK_COUNT even though they participate normally in DPCD capability
exchange and link training.

Treating sink_count == 0 as a permanent disconnect is valid for external
DisplayPort, but it breaks eDP probe/enable paths in
msm_dp_display_prepare_link().

Use drm_dp_read_sink_count_cap() in msm_dp_link_parse_sink_status_field()
and set link->sink_count to 1 when the capability is not available.

In dp_panel.c, msm_dp_panel_read_link_caps() still reads DP_SINK_COUNT
for branch devices. That read is left unchanged here: the sink on the
tested board reports DPCD 1.4 and does not advertise a downstream port,
so that path is not taken.

Signed-off-by: Vivek Kumar <vk092kumar@gmail.com>
Assisted-by : LLM
---
 drivers/gpu/drm/msm/dp/dp_display.c |  6 ++++--
 drivers/gpu/drm/msm/dp/dp_link.c    | 30 +++++++++++++++++++++--------
 drivers/gpu/drm/msm/dp/dp_link.h    |  5 ++++-
 drivers/gpu/drm/msm/dp/dp_panel.c   |  5 +++++
 drivers/gpu/drm/msm/dp/dp_panel.h   |  1 +
 5 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index 4dcbd9b99d06..2ae4dafd755f 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -290,7 +290,8 @@ static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
 			return -ETIMEDOUT;
 	}
 
-	msm_dp_link_process_request(dp->link);
+	msm_dp_link_process_request(dp->link, connector, dp->panel->dpcd,
+					 &dp->panel->desc);
 
 	if (!dp->msm_dp_display.is_edp)
 		drm_dp_set_subconnector_property(connector,
@@ -506,7 +507,8 @@ static int msm_dp_irq_hpd_handle(struct msm_dp_display_private *dp)
 			dp->link->sink_count);
 
 	/* check for any test request issued by sink */
-	rc = msm_dp_link_process_request(dp->link);
+	rc = msm_dp_link_process_request(dp->link, dp->msm_dp_display.connector,
+					 dp->panel->dpcd, &dp->panel->desc);
 	if (!rc) {
 		sink_request = dp->link->sink_request;
 		drm_dbg_dp(dp->drm_dev, "sink_request=%d\n", sink_request);
diff --git a/drivers/gpu/drm/msm/dp/dp_link.c b/drivers/gpu/drm/msm/dp/dp_link.c
index 34a91e194a12..f7f25020cacb 100644
--- a/drivers/gpu/drm/msm/dp/dp_link.c
+++ b/drivers/gpu/drm/msm/dp/dp_link.c
@@ -715,17 +715,25 @@ static int msm_dp_link_parse_request(struct msm_dp_link_private *link)
 	return ret;
 }
 
-static int msm_dp_link_parse_sink_status_field(struct msm_dp_link_private *link)
+static int msm_dp_link_parse_sink_status_field(struct msm_dp_link_private *link,
+						      struct drm_connector *connector,
+						      const u8 *dpcd,
+						      const struct drm_dp_desc *desc)
 {
 	int ret;
 
 	link->prev_sink_count = link->msm_dp_link.sink_count;
-	ret = drm_dp_read_sink_count(link->aux);
-	if (ret < 0) {
-		DRM_ERROR("DP parse sink count failed\n");
-		return ret;
+
+	if (drm_dp_read_sink_count_cap(connector, dpcd, desc)) {
+		ret = drm_dp_read_sink_count(link->aux);
+		if (ret < 0) {
+			DRM_ERROR("DP parse sink count failed\n");
+			return ret;
+		}
+		link->msm_dp_link.sink_count = ret;
+	} else {
+		link->msm_dp_link.sink_count = 1;
 	}
-	link->msm_dp_link.sink_count = ret;
 
 	ret = drm_dp_dpcd_read_link_status(link->aux,
 					   link->link_status);
@@ -1025,12 +1033,18 @@ static void msm_dp_link_reset_data(struct msm_dp_link_private *link)
 /**
  * msm_dp_link_process_request() - handle HPD IRQ transition to HIGH
  * @msm_dp_link: pointer to link module data
+ * @connector: connector the sink is attached to
+ * @dpcd: receiver capability DPCD of the sink
+ * @desc: DP descriptor of the sink
  *
  * This function will handle the HPD IRQ state transitions from LOW to HIGH
  * (including cases when there are back to back HPD IRQ HIGH) indicating
  * the start of a new link training request or sink status update.
  */
-int msm_dp_link_process_request(struct msm_dp_link *msm_dp_link)
+int msm_dp_link_process_request(struct msm_dp_link *msm_dp_link,
+				       struct drm_connector *connector,
+				       const u8 *dpcd,
+				       const struct drm_dp_desc *desc)
 {
 	int ret = 0;
 	struct msm_dp_link_private *link;
@@ -1044,7 +1058,7 @@ int msm_dp_link_process_request(struct msm_dp_link *msm_dp_link)
 
 	msm_dp_link_reset_data(link);
 
-	ret = msm_dp_link_parse_sink_status_field(link);
+	ret = msm_dp_link_parse_sink_status_field(link, connector, dpcd, desc);
 	if (ret)
 		return ret;
 
diff --git a/drivers/gpu/drm/msm/dp/dp_link.h b/drivers/gpu/drm/msm/dp/dp_link.h
index 76125e9c07e9..217fc5eb0a68 100644
--- a/drivers/gpu/drm/msm/dp/dp_link.h
+++ b/drivers/gpu/drm/msm/dp/dp_link.h
@@ -113,7 +113,10 @@ static inline u32 msm_dp_link_bit_depth_to_bpp(u32 tbd)
 
 void msm_dp_link_reset_phy_params_vx_px(struct msm_dp_link *msm_dp_link);
 u32 msm_dp_link_get_test_bits_depth(struct msm_dp_link *msm_dp_link, u32 bpp);
-int msm_dp_link_process_request(struct msm_dp_link *msm_dp_link);
+int msm_dp_link_process_request(struct msm_dp_link *msm_dp_link,
+				       struct drm_connector *connector,
+				       const u8 *dpcd,
+				       const struct drm_dp_desc *desc);
 int msm_dp_link_get_colorimetry_config(struct msm_dp_link *msm_dp_link);
 int msm_dp_link_adjust_levels(struct msm_dp_link *msm_dp_link, u8 *link_status);
 bool msm_dp_link_send_test_response(struct msm_dp_link *msm_dp_link);
diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
index e76dad0f6663..50e278286e09 100644
--- a/drivers/gpu/drm/msm/dp/dp_panel.c
+++ b/drivers/gpu/drm/msm/dp/dp_panel.c
@@ -252,6 +252,11 @@ int msm_dp_panel_read_link_caps(struct msm_dp_panel *msm_dp_panel,
 		return rc;
 	}
 
+	rc = drm_dp_read_desc(panel->aux, &msm_dp_panel->desc,
+				 drm_dp_is_branch(msm_dp_panel->dpcd));
+	if (rc)
+		memset(&msm_dp_panel->desc, 0, sizeof(msm_dp_panel->desc));
+
 	bw_code = drm_dp_link_rate_to_bw_code(msm_dp_panel->link_info.rate);
 	if (!is_link_rate_valid(bw_code) ||
 			!is_lane_count_valid(msm_dp_panel->link_info.num_lanes) ||
diff --git a/drivers/gpu/drm/msm/dp/dp_panel.h b/drivers/gpu/drm/msm/dp/dp_panel.h
index 4519ac374220..e52847474f16 100644
--- a/drivers/gpu/drm/msm/dp/dp_panel.h
+++ b/drivers/gpu/drm/msm/dp/dp_panel.h
@@ -31,6 +31,7 @@ struct msm_dp_panel {
 	/* dpcd raw data */
 	u8 dpcd[DP_RECEIVER_CAP_SIZE];
 	u8 downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
+	struct drm_dp_desc desc;
 
 	struct msm_dp_link_info link_info;
 	struct drm_connector *connector;
-- 
2.56.0