Re: [PATCH v4 1/3] media: v4l2-mem2mem: Add a kref to the v4l2_m2m_dev structure
From: Ulf Hansson <hidden>
Date: 2025-12-30 13:39:50
Also in:
imx, linux-media, linux-pm, lkml
On Fri, 5 Dec 2025 at 02:55, [off-list ref] wrote:
From: Nicolas Dufresne <nicolas.dufresne@collabora.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@collabora.com> Signed-off-by: Ming Qian <redacted>
I certainly don't have the complete picture for how this needs to work. However, I was thinking that rather than using a kref and having to share two specific functions to update it (v4l2_m2m_get|put), couldn't we just use a device-link instead? Kind regards Uffe
quoted hunk ↗ jump to hunk
--- v4 - Add my Signed-off-by 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