[PATCH v5 02/10] drm/bridge: Add detect_ctx hook and drm_bridge_detect_ctx() helper

[Cristian Ciocaltea]

Add an atomic-aware .detect_ctx() callback to drm_bridge_funcs and a
drm_bridge_detect_ctx() helper that accepts an optional
drm_modeset_acquire_ctx.

This enables bridge drivers to perform operations requiring modeset
locking during connector detection, such as SCDC management for HDMI
2.0.  When both ->detect_ctx and ->detect are defined, the former takes
precedence.  When ctx is NULL, locking is managed internally with EDEADLK
retry.

Tested-by: Diederik de Haas <diederik at cknow-tech.com>
Tested-by: Maud Spierings <maud_spierings at hotmail.com>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea at collabora.com>
---
 drivers/gpu/drm/drm_bridge.c | 66 ++++++++++++++++++++++++++++++++++++++++----
 include/drm/drm_bridge.h     | 43 +++++++++++++++++++++++++----
 2 files changed, 98 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 986e4c79a4e0..a5c6c2ea4ba6 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -1361,9 +1361,9 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
  * @connector: attached connector
  *
  * If the bridge supports output detection, as reported by the
- * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect for the
- * bridge and return the connection status. Otherwise return
- * connector_status_unknown.
+ * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect_ctx
+ * or &drm_bridge_funcs.detect for the bridge and return the connection status.
+ * Otherwise return connector_status_unknown.
  *
  * RETURNS:
  * The detection status on success, or connector_status_unknown if the bridge
@@ -1372,12 +1372,68 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
 enum drm_connector_status
 drm_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector)
 {
+	return drm_bridge_detect_ctx(bridge, connector, NULL);
+}
+EXPORT_SYMBOL_GPL(drm_bridge_detect);
+
+/**
+ * drm_bridge_detect_ctx - check if anything is attached to the bridge output
+ * @bridge: bridge control structure
+ * @connector: attached connector
+ * @ctx: acquire_ctx, or NULL to let this function handle locking
+ *
+ * If the bridge supports output detection, as reported by the
+ * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect_ctx
+ * or &drm_bridge_funcs.detect for the bridge and return the connection status.
+ * Otherwise return connector_status_unknown.
+ *
+ * RETURNS:
+ * The detection status on success, or connector_status_unknown if the bridge
+ * doesn't support output detection.
+ * If @ctx is set, it might also return -EDEADLK.
+ */
+int drm_bridge_detect_ctx(struct drm_bridge *bridge,
+			  struct drm_connector *connector,
+			  struct drm_modeset_acquire_ctx *ctx)
+{
+	struct drm_modeset_acquire_ctx br_ctx;
+	int ret;
+
 	if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
 		return connector_status_unknown;
 
-	return bridge->funcs->detect(bridge, connector);
+	if (!bridge->funcs->detect_ctx)
+		return bridge->funcs->detect(bridge, connector);
+
+	if (ctx) {
+		ret = bridge->funcs->detect_ctx(bridge, connector, ctx);
+		if (ret == -EDEADLK)
+			return ret;
+
+		goto out;
+	}
+
+	drm_modeset_acquire_init(&br_ctx, 0);
+retry:
+	ret = drm_modeset_lock(&connector->dev->mode_config.connection_mutex,
+			       &br_ctx);
+	if (!ret)
+		ret = bridge->funcs->detect_ctx(bridge, connector, &br_ctx);
+
+	if (ret == -EDEADLK) {
+		drm_modeset_backoff(&br_ctx);
+		goto retry;
+	}
+
+	drm_modeset_drop_locks(&br_ctx);
+	drm_modeset_acquire_fini(&br_ctx);
+out:
+	if (WARN_ON(ret < 0))
+		ret = connector_status_unknown;
+
+	return ret;
 }
-EXPORT_SYMBOL_GPL(drm_bridge_detect);
+EXPORT_SYMBOL_GPL(drm_bridge_detect_ctx);
 
 /**
  * drm_bridge_get_modes - fill all modes currently valid for the sink into the
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index d6cd0f5af045..6c751b96c3c9 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -535,10 +535,12 @@ struct drm_bridge_funcs {
 	 *
 	 * Check if anything is attached to the bridge output.
 	 *
-	 * This callback is optional, if not implemented the bridge will be
-	 * considered as always having a component attached to its output.
-	 * Bridges that implement this callback shall set the
-	 * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
+	 * This is the non-atomic version of detect_ctx() callback, and is
+	 * optional. If both are implemented, it is ignored. If none is
+	 * implemented, the bridge will be considered as always having a
+	 * component attached to its output. Bridges that implement this
+	 * callback shall set the DRM_BRIDGE_OP_DETECT flag in their
+	 * &drm_bridge->ops.
 	 *
 	 * RETURNS:
 	 *
@@ -547,6 +549,32 @@ struct drm_bridge_funcs {
 	enum drm_connector_status (*detect)(struct drm_bridge *bridge,
 					    struct drm_connector *connector);
 
+	/**
+	 * @detect_ctx:
+	 *
+	 * Check if anything is attached to the bridge output.
+	 *
+	 * This is the atomic version of detect() callback, and is optional.
+	 * If both are implemented, it takes precedence. If none is implemented,
+	 * the bridge will be considered as always having a component attached
+	 * to its output. Bridges that implement this callback shall set the
+	 * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
+	 *
+	 * To avoid races against concurrent connector state updates, the
+	 * helper libraries always call this with ctx set to a valid context,
+	 * and &drm_mode_config.connection_mutex will always be locked with
+	 * the ctx parameter set to this ctx. This allows taking additional
+	 * locks as required.
+	 *
+	 * RETURNS:
+	 *
+	 * &drm_connector_status indicating the bridge output status,
+	 * or the error code returned by drm_modeset_lock(), -EDEADLK.
+	 */
+	int (*detect_ctx)(struct drm_bridge *bridge,
+			  struct drm_connector *connector,
+			  struct drm_modeset_acquire_ctx *ctx);
+
 	/**
 	 * @get_modes:
 	 *
@@ -1002,8 +1030,8 @@ struct drm_bridge_timings {
 enum drm_bridge_ops {
 	/**
 	 * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
-	 * its output. Bridges that set this flag shall implement the
-	 * &drm_bridge_funcs->detect callback.
+	 * its output. Bridges that set this flag shall implement either the
+	 * &drm_bridge_funcs->detect or &drm_bridge_funcs->detect_ctx callbacks.
 	 */
 	DRM_BRIDGE_OP_DETECT = BIT(0),
 	/**
@@ -1565,6 +1593,9 @@ drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
 
 enum drm_connector_status
 drm_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector);
+int drm_bridge_detect_ctx(struct drm_bridge *bridge,
+			  struct drm_connector *connector,
+			  struct drm_modeset_acquire_ctx *ctx);
 int drm_bridge_get_modes(struct drm_bridge *bridge,
 			 struct drm_connector *connector);
 const struct drm_edid *drm_bridge_edid_read(struct drm_bridge *bridge,

-- 
2.53.0