[PATCH v5 17/18] drm/bridge: analogix_dp: Handle HPD notification from downstream bridge

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

When the display pipeline includes a display-connector bridge with
hpd-gpios configured, the connector's hotplug status is managed by the
display-connector bridge through its GPIO, not by the Analogix DP
controller's native HPD. In this configuration, the DP controller's
internal HPD polling in analogix_dp_detect_hpd() does not reflect the
actual connection state.

At attach time, detect whether a downstream bridge provides HPD events
(DRM_BRIDGE_OP_HPD) while none of them provides detection
(DRM_BRIDGE_OP_DETECT). When found, switch to hpd notify mode: cache
the connection status reported through the .hpd_notify callback, mute
the controller's native HPD interrupts and skip their initialization,
and trust the cached status instead of polling the typically
unconnected native HPD pin.

Suggested-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/all/5609825.iZASKD2KPV@diego/
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Damon Ding <damon.ding@rock-chips.com>

---

Changes in v3:
- Introduce hpd_notify_mode flag to skip native HPD operations when
  HPD comes from a downstream bridge.

Changes in v4:
- Add Tested-by tag.

Changes in v5:
- Return the connector status directly from analogix_dp_bridge_detect()
  in the hpd notify mode, to avoid the race where the hpd_notify() echo
  of the detect path overwrites a newer notification cached by
  analogix_dp_bridge_notify(). (Sashiko)
---
 .../drm/bridge/analogix/analogix_dp_core.c    | 31 ++++++++++++++++++-
 .../drm/bridge/analogix/analogix_dp_core.h    |  2 ++
 .../gpu/drm/bridge/analogix/analogix_dp_reg.c |  7 +++--
 3 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index 938c70dc8e15..9e6e83357232 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -52,7 +52,8 @@ static const bool verify_fast_training;
 static bool analogix_dp_require_pm_for_hpd_irq(struct analogix_dp_device *dp)
 {
 	return (dp->plat_data->dev_type == RK3576_EDP || dp->plat_data->dev_type == RK3588_EDP) &&
-	       !dp->hpd_gpiod && !dp->force_hpd && !dp->force_connected_mode;
+	       !dp->hpd_gpiod && !dp->force_hpd && !dp->force_connected_mode &&
+	       !dp->hpd_notify_mode;
 }
 
 static void analogix_dp_init_dp(struct analogix_dp_device *dp)
@@ -925,6 +926,9 @@ analogix_dp_bridge_detect(struct drm_bridge *bridge, struct drm_connector *conne
 	enum drm_connector_status status = connector_status_disconnected;
 	int ret;
 
+	if (dp->hpd_notify_mode)
+		return connector->status;
+
 	if (dp->force_connected_mode)
 		return connector_status_connected;
 
@@ -959,6 +963,21 @@ static bool analogix_dp_bridge_force_connected(struct analogix_dp_device *dp)
 	return force_connected;
 }
 
+static bool analogix_dp_has_downstream_hpd(struct analogix_dp_device *dp)
+{
+	bool hpd_bridge = false;
+
+	drm_for_each_bridge_in_chain_from(dp->bridge.next_bridge, bridge) {
+		if (bridge->ops & DRM_BRIDGE_OP_DETECT)
+			return false;
+
+		if (bridge->ops & DRM_BRIDGE_OP_HPD)
+			hpd_bridge = true;
+	}
+
+	return hpd_bridge;
+}
+
 static int analogix_dp_bridge_attach(struct drm_bridge *bridge,
 				     struct drm_encoder *encoder,
 				     enum drm_bridge_attach_flags flags)
@@ -987,6 +1006,7 @@ static int analogix_dp_bridge_attach(struct drm_bridge *bridge,
 		 * accurate hotplug state.
 		 */
 		dp->force_connected_mode = analogix_dp_bridge_force_connected(dp);
+		dp->hpd_notify_mode = analogix_dp_has_downstream_hpd(dp);
 	}
 
 	return 0;
@@ -1283,6 +1303,14 @@ static void analogix_dp_bridge_atomic_post_disable(struct drm_bridge *bridge,
 		DRM_ERROR("Failed to enable psr (%d)\n", ret);
 }
 
+static void analogix_dp_bridge_notify(struct drm_bridge *bridge, struct drm_connector *connector,
+				      enum drm_connector_status status)
+{
+	struct analogix_dp_device *dp = to_dp(bridge);
+
+	dp->connection_notified = (status == connector_status_connected);
+}
+
 static void analogix_dp_bridge_hpd_enable(struct drm_bridge *bridge)
 {
 }
@@ -1303,6 +1331,7 @@ static const struct drm_bridge_funcs analogix_dp_bridge_funcs = {
 	.attach = analogix_dp_bridge_attach,
 	.edid_read = analogix_dp_bridge_edid_read,
 	.detect = analogix_dp_bridge_detect,
+	.hpd_notify = analogix_dp_bridge_notify,
 	.hpd_enable = analogix_dp_bridge_hpd_enable,
 	.hpd_disable = analogix_dp_bridge_hpd_disable,
 };
diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
index 2ac92b2bac0a..04db14a91074 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
@@ -171,6 +171,8 @@ struct analogix_dp_device {
 	bool			fast_train_enable;
 	bool			psr_supported;
 	bool			force_connected_mode;
+	bool			hpd_notify_mode;
+	bool			connection_notified;
 
 	u8 dpcd[DP_RECEIVER_CAP_SIZE];
 
diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
index af5e5a8ec88d..501360a175d5 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
@@ -193,7 +193,7 @@ void analogix_dp_config_interrupt(struct analogix_dp_device *dp)
 	writel(0, dp->reg_base + ANALOGIX_DP_COMMON_INT_MASK_2);
 	writel(0, dp->reg_base + ANALOGIX_DP_COMMON_INT_MASK_3);
 
-	if (dp->hpd_gpiod) {
+	if (dp->hpd_gpiod || dp->hpd_notify_mode) {
 		analogix_dp_mute_hpd_interrupt(dp, HPD_IRQ_ALL);
 		return;
 	}
@@ -435,7 +435,7 @@ void analogix_dp_init_hpd(struct analogix_dp_device *dp)
 {
 	u32 reg;
 
-	if (dp->hpd_gpiod)
+	if (dp->hpd_gpiod || dp->hpd_notify_mode)
 		return;
 
 	analogix_dp_clear_hotplug_interrupts(dp, HPD_IRQ_ALL);
@@ -536,6 +536,9 @@ int analogix_dp_get_plug_in_status(struct analogix_dp_device *dp)
 	if (dp->hpd_gpiod) {
 		if (gpiod_get_value(dp->hpd_gpiod))
 			return 0;
+	} else if (dp->hpd_notify_mode) {
+		if (dp->connection_notified)
+			return 0;
 	} else {
 		reg = readl(dp->reg_base + ANALOGIX_DP_SYS_CTL_3);
 		if (reg & HPD_STATUS)
-- 
2.34.1