On Fri Dec 5 09:54:24 2025 +0800, Nicolas Dufresne wrote:
> Adding a reference count to the v4l2_m2m_dev structure allow safely
> sharing it across multiple hardware nodes. This can be used to prevent
> running jobs concurrently on m2m cores that have some internal resource
> sharing.
>
> Signed-off-by: Ming Qian <[email protected]>
> Reviewed-by: Frank Li <[email protected]>
> Signed-off-by: Nicolas Dufresne <[email protected]>
> Signed-off-by: Hans Verkuil <[email protected]>
> [hverkuil: fix typos in v4l2_m2m_put documentation]
Patch committed.
Thanks,
Hans Verkuil
drivers/media/v4l2-core/v4l2-mem2mem.c | 23 +++++++++++++++++++++++
include/media/v4l2-mem2mem.h | 21 +++++++++++++++++++++
2 files changed, 44 insertions(+)
---
diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c
b/drivers/media/v4l2-core/v4l2-mem2mem.c
index fec93c1a9231..ae0de54d4c3e 100644
--- a/drivers/media/v4l2-core/v4l2-mem2mem.c
+++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
@@ -90,6 +90,7 @@ static const char * const m2m_entity_name[] = {
* @job_work: worker to run queued jobs.
* @job_queue_flags: flags of the queue status, %QUEUE_PAUSED.
* @m2m_ops: driver callbacks
+ * @kref: device reference count
*/
struct v4l2_m2m_dev {
struct v4l2_m2m_ctx *curr_ctx;
@@ -109,6 +110,8 @@ struct v4l2_m2m_dev {
unsigned long job_queue_flags;
const struct v4l2_m2m_ops *m2m_ops;
+
+ struct kref kref;
};
static struct v4l2_m2m_queue_ctx *get_queue_ctx(struct v4l2_m2m_ctx *m2m_ctx,
@@ -1200,6 +1203,7 @@ struct v4l2_m2m_dev *v4l2_m2m_init(const struct
v4l2_m2m_ops *m2m_ops)
INIT_LIST_HEAD(&m2m_dev->job_queue);
spin_lock_init(&m2m_dev->job_spinlock);
INIT_WORK(&m2m_dev->job_work, v4l2_m2m_device_run_work);
+ kref_init(&m2m_dev->kref);
return m2m_dev;
}
@@ -1211,6 +1215,25 @@ void v4l2_m2m_release(struct v4l2_m2m_dev *m2m_dev)
}
EXPORT_SYMBOL_GPL(v4l2_m2m_release);
+void v4l2_m2m_get(struct v4l2_m2m_dev *m2m_dev)
+{
+ kref_get(&m2m_dev->kref);
+}
+EXPORT_SYMBOL_GPL(v4l2_m2m_get);
+
+static void v4l2_m2m_release_from_kref(struct kref *kref)
+{
+ struct v4l2_m2m_dev *m2m_dev = container_of(kref, struct v4l2_m2m_dev,
kref);
+
+ v4l2_m2m_release(m2m_dev);
+}
+
+void v4l2_m2m_put(struct v4l2_m2m_dev *m2m_dev)
+{
+ kref_put(&m2m_dev->kref, v4l2_m2m_release_from_kref);
+}
+EXPORT_SYMBOL_GPL(v4l2_m2m_put);
+
struct v4l2_m2m_ctx *v4l2_m2m_ctx_init(struct v4l2_m2m_dev *m2m_dev,
void *drv_priv,
int (*queue_init)(void *priv, struct vb2_queue *src_vq, struct
vb2_queue *dst_vq))
diff --git a/include/media/v4l2-mem2mem.h b/include/media/v4l2-mem2mem.h
index bf6a09a04dcf..31de25d792b9 100644
--- a/include/media/v4l2-mem2mem.h
+++ b/include/media/v4l2-mem2mem.h
@@ -547,6 +547,27 @@ v4l2_m2m_register_media_controller(struct v4l2_m2m_dev
*m2m_dev,
*/
void v4l2_m2m_release(struct v4l2_m2m_dev *m2m_dev);
+/**
+ * v4l2_m2m_get() - take a reference to the m2m_dev structure
+ *
+ * @m2m_dev: opaque pointer to the internal data to handle M2M context
+ *
+ * This is used to share the M2M device across multiple devices. This
+ * can be used to avoid scheduling two hardware nodes concurrently.
+ */
+void v4l2_m2m_get(struct v4l2_m2m_dev *m2m_dev);
+
+/**
+ * v4l2_m2m_put() - remove a reference to the m2m_dev structure
+ *
+ * @m2m_dev: opaque pointer to the internal data to handle M2M context
+ *
+ * Once the M2M device has no more references, v4l2_m2m_release() will be
+ * called automatically. Users of this method should never call
+ * v4l2_m2m_release() directly. See v4l2_m2m_get() for more details.
+ */
+void v4l2_m2m_put(struct v4l2_m2m_dev *m2m_dev);
+
/**
* v4l2_m2m_ctx_init() - allocate and initialize a m2m context
*
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