Hi Luca,

On 1/14/26 12:08 PM, Luca Ceresoli wrote:

Hello Cristian,

On Mon Jan 12, 2026 at 11:26 PM CET, Cristian Ciocaltea wrote:

quoted

Add an atomic variant of the ->detect callback and a new helper to call
the hook while passing an optional drm_modeset_acquire_ctx reference.

When both ->detect_ctx and ->detect are defined, the latter is ignored.
If acquire_ctx is unset, the function takes care of the locking,
while also handling EDEADLK.

Tested-by: Diederik de Haas <redacted>
Tested-by: Maud Spierings <redacted>
Signed-off-by: Cristian Ciocaltea <redacted>
---
 drivers/gpu/drm/drm_bridge.c | 58 ++++++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_bridge.h     | 30 +++++++++++++++++++++++
 2 files changed, 88 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 6dcf8f6d3ecf..0ef12bf98011 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c

@@ -1344,6 +1344,64 @@ drm_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector)
 }
 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.
+ *
+ * When both @ctx and &drm_bridge_funcs.detect_ctx are not set, this helper
+ * function is equivalent to drm_bridge_detect() above.
+ *
+ * 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)

Shouldn't this new function return the same type as detect, i.e. enum
drm_connector_status?

No, because it might also return an error, as documented in the RETURNS section.
Please also check the comments below.

Otherwise (see below)...

quoted

+{
+	if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
+		return connector_status_unknown;
+
+	if (bridge->funcs->detect_ctx) {
+		struct drm_modeset_acquire_ctx br_ctx;
+		int ret;
+
+		if (ctx)
+			return bridge->funcs->detect_ctx(bridge, connector, ctx);
+
+		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;
+		}
+
+		if (ret < 0)
+			ret = connector_status_unknown;
+
+		drm_modeset_drop_locks(&br_ctx);
+		drm_modeset_acquire_fini(&br_ctx);
+
+		return ret;
+	}
+
+	return bridge->funcs->detect(bridge, connector);

...here you're converting an enum into an int, which is ok-isk but not
ideal.

We already have a similar approach with drm_connector_helper_funcs.detect_ctx()
which is expected to return drm_connector_status or the error from
drm_modeset_lock().

quoted

--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h

@@ -664,6 +664,33 @@ 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 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 atomic version of &drm_bridge_funcs.detect.

I may be missing something, but I'm a bit puzzled by the "atomic" word
here. For other funcs in this struct there's the old non-atomic func X and
the new atomic_X func that receives a pointer to struct drm_atomic_state.

Here I think you are using "atomic" with a more generic meaning. Maybe we'd
better use another wording to not confuse readers?

This is once again consistent with drm_connector_helper_funcs.detect_ctx()
stating:

  "This is the atomic version of &drm_connector_funcs.detect."

I'm open for changes, but then we should probably do this across all relevant
funcs, beyond current struct scope.

quoted

+	 *
+	 * 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);

As above, shouldn't this new func return the same type as detect?

Nope, as explained above.

Thanks,
Cristian