[PATCH v5 03/18] drm/bridge: analogix_dp: Restrict forced connected status to panel endpoints

[Damon Ding]

Limit the forced connected status so that it only applies when the
bridge chain ends with a panel and no downstream bridge supports
DRM_BRIDGE_OP_DETECT, which is tracked by the new
&analogix_dp_device.force_connected_mode.  For all the other cases,
rely on analogix_dp_detect_hpd() to report the 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.

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

Reported-by: Heiko Stuebner <heiko at sntech.de>
Link: https://lore.kernel.org/all/5209243.oAaWjsssbx@diego/
Tested-by: Heiko Stuebner <heiko at sntech.de>
Signed-off-by: Damon Ding <damon.ding at rock-chips.com>

---

Changes in v3:
- Add missing drm_bridge_put() after drm_bridge_chain_get_last_bridge()
  to fix a reference count leak. (Sashiko)
- Report panel endpoints as always connected from
  analogix_dp_get_plug_in_status() via newly added
  &analogix_dp_device.force_connected_mode.

Changes in v4:
- Add Tested-by tag.

Changes in v5:
- Move the force_connected_mode check from
  analogix_dp_get_plug_in_status() to analogix_dp_bridge_detect(), as
  the hardware status reader is also used by the force HPD fallback
  and the AUX HPD waiting paths. (Sashiko)
- Hold a runtime PM reference in analogix_dp_bridge_detect(), since
  analogix_dp_detect_hpd() may access the registers while the device
  is runtime suspended. (Sashiko)
---
 .../drm/bridge/analogix/analogix_dp_core.c    | 37 ++++++++++++++++++-
 .../drm/bridge/analogix/analogix_dp_core.h    |  1 +
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index 19f3cec5a691..35b273a803a0 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -904,16 +904,42 @@ 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;
+	int ret;
 
-	if (dp->bridge.next_bridge)
+	if (dp->force_connected_mode)
 		return connector_status_connected;
 
+	ret = pm_runtime_resume_and_get(dp->dev);
+	if (ret)
+		return connector_status_unknown;
+
 	if (!analogix_dp_detect_hpd(dp))
 		status = connector_status_connected;
 
+	pm_runtime_mark_last_busy(dp->dev);
+	pm_runtime_put_autosuspend(dp->dev);
+
 	return status;
 }
 
+static bool analogix_dp_bridge_force_connected(struct analogix_dp_device *dp)
+{
+	struct drm_bridge *last_bridge;
+	bool force_connected = false;
+
+	drm_for_each_bridge_in_chain_from(dp->bridge.next_bridge, bridge) {
+		if (bridge->ops & DRM_BRIDGE_OP_DETECT)
+			return false;
+	}
+
+	last_bridge = drm_bridge_chain_get_last_bridge(dp->encoder);
+	if (last_bridge)
+		force_connected = drm_bridge_is_panel(last_bridge);
+	drm_bridge_put(last_bridge);
+
+	return force_connected;
+}
+
 static int analogix_dp_bridge_attach(struct drm_bridge *bridge,
 				     struct drm_encoder *encoder,
 				     enum drm_bridge_attach_flags flags)
@@ -933,6 +959,15 @@ 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;
 		}
+
+		/*
+		 * 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 back to analogix_dp_detect_hpd() to report
+		 * accurate hotplug state.
+		 */
+		dp->force_connected_mode = analogix_dp_bridge_force_connected(dp);
 	}
 
 	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 4560597604ad..64aaba67e669 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
@@ -170,6 +170,7 @@ struct analogix_dp_device {
 	bool			force_hpd;
 	bool			fast_train_enable;
 	bool			psr_supported;
+	bool			force_connected_mode;
 
 	u8 dpcd[DP_RECEIVER_CAP_SIZE];
 
-- 
2.34.1