linux-kernel - [PATCH v3 1/3] media: v4l2-mem2mem: Add a kref to the v4l2_m2m

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Message-ID: <20251204090813.595-1-ming.qian@oss.nxp.com>
Date: Thu,  4 Dec 2025 17:08:09 +0800
From: ming.qian@....nxp.com
To: linux-media@...r.kernel.org
Cc: mchehab@...nel.org,
	hverkuil-cisco@...all.nl,
	nicolas@...fresne.ca,
	benjamin.gaignard@...labora.com,
	p.zabel@...gutronix.de,
	sebastian.fricke@...labora.com,
	shawnguo@...nel.org,
	ulf.hansson@...aro.org,
	s.hauer@...gutronix.de,
	kernel@...gutronix.de,
	festevam@...il.com,
	linux-imx@....com,
	l.stach@...gutronix.de,
	Frank.li@....com,
	peng.fan@....com,
	eagle.zhou@....com,
	imx@...ts.linux.dev,
	linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v3 1/3] media: v4l2-mem2mem: Add a kref to the v4l2_m2m_dev structure

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

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: Nicolas Dufresne <nicolas.dufresne@...labora.com>
---
 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..ca295c660c7f 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 have no more references, v4l2_m2m_realse() 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
  *
-- 
2.52.0