[PATCH 6.18 084/314] media: v4l2-mem2mem: Add a kref to the v4l2_m2m_dev structure

Sasha Levin
2026-03-10T11:26:00Z

From: Nicolas Dufresne <nicolas.dufresne@collabora.com>

[ Upstream commit db6b97a4f8041e479be9ef4b8b07022636c96f50 ]

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 <ming.qian@oss.nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
[hverkuil: fix typos in v4l2_m2m_put documentation]
Stable-dep-of: e0203ddf9af7 ("media: verisilicon: Avoid G2 bus error while decoding H.264 and HEVC")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 21acd9bc86071..bc8218d1cab9f 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,
@@ -1206,6 +1209,7 @@ 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;
}
@@ -1217,6 +1221,25 @@ 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 500f81f399dfa..08e3c9c4f1e9d 100644
--- a/include/media/v4l2-mem2mem.h
+++ b/include/media/v4l2-mem2mem.h
@@ -544,6 +544,27 @@ 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
*
--
2.51.0