[PATCH v2 09/10] drm/bridge: analogix_dp: Restrict forced connected status only for panel endpoint

[Damon Ding <damon.ding@rock-chips.com>]

Limit the shortcut which unconditionally returns connected status when
a next bridge exists. Only apply this logic if the last bridge in the
chain is a panel. For all other cases, rely on analogix_dp_detect_hpd()
to report accurate hotplug state.

Background for the special handling:
- If the chain ends with a DP connector bridge, the connector relies
on analogix_dp to perform detection. We must avoid hardcoding connected
status here.
- For intermediate bridges such as PS8625 / PTN3460 without detect
support [1], historically the bridge connector defaults to connected
via drm_helper_probe_detect() when no per-bridge detect callback
exists. Maintain compatibility by keeping the shortcut exclusively for
panel endpoints.

[1] https://lore.kernel.org/all/4939d55e-b560-4235-8295-adf8e48d9b74@samsung.com/

Reported-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/all/5209243.oAaWjsssbx@diego/
Signed-off-by: Damon Ding <damon.ding@rock-chips.com>
---
 .../gpu/drm/bridge/analogix/analogix_dp_core.c   | 16 ++++++++++++++--
 .../gpu/drm/bridge/analogix/analogix_dp_core.h   |  1 +
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index f05db455b430..a5a50b9ab8a7 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -906,8 +906,15 @@ analogix_dp_bridge_detect(struct drm_bridge *bridge, struct drm_connector *conne
 	struct analogix_dp_device *dp = to_dp(bridge);
 	enum drm_connector_status status = connector_status_disconnected;
 
-	if (dp->plat_data->next_bridge)
-		return connector_status_connected;
+	/*
+	 * Only assume connected when the bridge chain ends with a panel.
+	 * Panel bridges lack a detect callback and historically rely on
+	 * this shortcut. For other next bridge types (e.g., DP connector
+	 * bridges), fall through to analogix_dp_detect_hpd() to report
+	 * accurate hotplug state.
+	 */
+	if (dp->plat_data->next_bridge && dp->last_bridge_is_panel)
+		status = connector_status_connected;
 
 	if (!analogix_dp_detect_hpd(dp))
 		status = connector_status_connected;
@@ -920,6 +927,7 @@ static int analogix_dp_bridge_attach(struct drm_bridge *bridge,
 				     enum drm_bridge_attach_flags flags)
 {
 	struct analogix_dp_device *dp = to_dp(bridge);
+	struct drm_bridge *last_bridge;
 	int ret = 0;
 
 	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)) {
@@ -934,6 +942,10 @@ static int analogix_dp_bridge_attach(struct drm_bridge *bridge,
 			dev_err(dp->dev, "failed to attach following panel or bridge (%d)\n", ret);
 			return ret;
 		}
+
+		last_bridge = drm_bridge_chain_get_last_bridge(dp->encoder);
+		if (drm_bridge_is_panel(last_bridge))
+			dp->last_bridge_is_panel = true;
 	}
 
 	return 0;
diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
index 2066e575ce10..bcb5674801a2 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
@@ -168,6 +168,7 @@ struct analogix_dp_device {
 	bool			force_hpd;
 	bool			fast_train_enable;
 	bool			psr_supported;
+	bool			last_bridge_is_panel;
 
 	u8 dpcd[DP_RECEIVER_CAP_SIZE];
 
-- 
2.34.1