[PATCH] media: v4l2-async: link ancillary device runtime PM to the sensor's

[Cédric Bellegarde]

When a sensor's fwnode references an ancillary lens or flash device
(e.g. via the "lens-focus" or "flash-leds" properties),
v4l2_async_create_ancillary_links() already creates a media controller
link between the two entities, but their runtime PM states remain
independent.

This is a problem for devices such as VCM lens actuators, which are
typically spring-loaded: holding a position away from the spring's
rest point requires continuous power, and the position is not retained
once power is cut. If such an actuator is allowed to runtime-suspend
independently of the sensor, the lens can drift back to its rest
position during an otherwise active capture session.

Add V4L2_SUBDEV_FL_PM_LINK to allow an ancillary subdevice to request
that its runtime PM state be linked to the associated sensor.

Signed-off-by: Cédric Bellegarde <cedric.bellegarde@xxxxxxxxxxxx>
---
Link runtime PM of ancillary devices such as lens actuators to their associated sensor,
while allowing actuators to autosuspend when idle.

Example usage:
https://gitlab.com/gnumdk/linux/-/commit/82b2d71415a1d95b2170e19ce025afc8bbdcf145
---
 drivers/media/v4l2-core/v4l2-async.c | 18 ++++++++++++++----
 include/media/v4l2-subdev.h          |  7 +++++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
index 460bf3dbbb88..22df627153b8 100644
--- a/drivers/media/v4l2-core/v4l2-async.c
+++ b/drivers/media/v4l2-core/v4l2-async.c
@@ -318,6 +318,7 @@ static int v4l2_async_create_ancillary_links(struct v4l2_async_notifier *n,
 {
 #if IS_ENABLED(CONFIG_MEDIA_CONTROLLER)
 	struct media_link *link;
+	struct device_link *devlink;
 
 	if (sd->entity.function != MEDIA_ENT_F_LENS &&
 	    sd->entity.function != MEDIA_ENT_F_FLASH)
@@ -331,11 +332,20 @@ static int v4l2_async_create_ancillary_links(struct v4l2_async_notifier *n,
 	}
 
 	link = media_create_ancillary_link(&n->sd->entity, &sd->entity);
-
-	return IS_ERR(link) ? PTR_ERR(link) : 0;
-#else
-	return 0;
+	if (IS_ERR(link))
+		return PTR_ERR(link);
+
+	if (sd->flags & V4L2_SUBDEV_FL_PM_LINK) {
+		devlink = device_link_add(n->sd->dev, sd->dev,
+					  DL_FLAG_PM_RUNTIME |
+					  DL_FLAG_AUTOREMOVE_CONSUMER);
+		if (!devlink)
+			dev_warn(notifier_dev(n),
+				 "failed to link power management of %s to %s\n",
+				 dev_name(sd->dev), dev_name(n->sd->dev));
+	}
 #endif
+	return 0;
 }
 
 static int v4l2_async_match_notify(struct v4l2_async_notifier *notifier,
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index d256b7ec8f84..9f64b10afd10 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -972,6 +972,13 @@ struct v4l2_subdev_internal_ops {
  * - Multiple streams per pad are supported
  */
 #define V4L2_SUBDEV_FL_STREAMS			(1U << 4)
+/*
+ * Set this flag to keep the subdevice active while its associated sensor is active.
+ *
+ * This is intended for ancillary devices, such as lens actuators, whose
+ * hardware state or physical position cannot be retained while powered off.
+ */
+#define V4L2_SUBDEV_FL_PM_LINK          (1U << 5)
 
 struct regulator_bulk_data;
 

---
base-commit: df2908090cda368b01ff43709f51890076c56157
change-id: 20260911-sensors_pm-787eac01aa18

Best regards,
-- 
Cédric Bellegarde <cedric.bellegarde@xxxxxxxxxxxx>