Re: [PATCH 05/17] media: v4l2-mem2mem: support running multiple jobs in parallel

Hi Sven !

On Friday, 5 June 2026 18:06:51 EDT Sven Püschel wrote:
> Add support for running multiple jobs in parallel for SoCs containing
> multiple identical devices. An example is the Rockchip RK3588 SoC,
> which contains two identical RGA3 devices. Therefore it is desirable to
> have the kernel schedule the work across all available devices and only
> expose one video device to the userspace.
> 
> Previously the curr_ctx member of a v4l2_m2m_dev was used to track the
> currently running context. But the currently running context will always
> be at the top of the job_queue. As the TRANS_RUNNING flag can be used to
> check if the queue head is already running, the curr_ctx member can be
> completely dropped
> 
> To avoid queueing too many parallel jobs, the
> v4l2_m2m_set_max_parallel_jobs method is added. It allows a driver
> to set the number of parallel jobs and avoids calling device_run when
> the given number of jobs is already running. This is set to 1 by default
> to prevent parallel job runs. Drivers with the need and support for
> scheduling jobs can adjust this value accordingly.
> 
> Note that this change doesn't allow a context to be used multiple times
> in parallel. So a single stream won't be able to utilize multiple devices
> at once, but N streams can utilize up to N devices. This is caused by the
> fact that a context is not added multiple times to the job_list and also
> holds the job_flags to distinguish if it's currently running.
> 
> Signed-off-by: Sven Püschel <[email protected]>
> ---
>  drivers/media/v4l2-core/v4l2-mem2mem.c | 89
> ++++++++++++++++++++++------------ include/media/v4l2-mem2mem.h           |
>  3 ++
>  2 files changed, 62 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c
> b/drivers/media/v4l2-core/v4l2-mem2mem.c index a65cbb124cfe0..14ac9c85803d1
> 100644
> --- a/drivers/media/v4l2-core/v4l2-mem2mem.c
> +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
> @@ -84,16 +84,15 @@ static const char * const m2m_entity_name[] = {
>   *			v4l2_m2m_unregister_media_controller().
>   * @intf_devnode:	&struct media_intf devnode pointer with the interface
>   *			with controls the M2M device.
> - * @curr_ctx:		currently running instance
>   * @job_queue:		instances queued to run
>   * @job_spinlock:	protects job_queue
>   * @job_work:		worker to run queued jobs.
>   * @job_queue_flags:	flags of the queue status, %QUEUE_PAUSED.
> + * @max_parallel_jobs:	max job_queue instances number marked as running
>   * @m2m_ops:		driver callbacks
>   * @kref:		device reference count
>   */
>  struct v4l2_m2m_dev {
> -	struct v4l2_m2m_ctx	*curr_ctx;
>  #ifdef CONFIG_MEDIA_CONTROLLER
>  	struct media_entity	*source;
>  	struct media_pad	source_pad;
> @@ -108,6 +107,7 @@ struct v4l2_m2m_dev {
>  	spinlock_t		job_spinlock;
>  	struct work_struct	job_work;
>  	unsigned long		job_queue_flags;
> +	u32			max_parallel_jobs;
> 
>  	const struct v4l2_m2m_ops *m2m_ops;
> 
> @@ -123,6 +123,12 @@ static struct v4l2_m2m_queue_ctx *get_queue_ctx(struct
> v4l2_m2m_ctx *m2m_ctx, return &m2m_ctx->cap_q_ctx;
>  }
> 
> +void v4l2_m2m_set_max_parallel_jobs(struct v4l2_m2m_dev *m2m_dev,
> +				    u32 max_parallel_jobs)
> +{
> +	m2m_dev->max_parallel_jobs = max_parallel_jobs;
> +}

This needs to be exported so that drivers can use it even when compiled as 
modules.
+EXPORT_SYMBOL(v4l2_m2m_set_max_parallel_jobs);

> +
>  struct vb2_queue *v4l2_m2m_get_vq(struct v4l2_m2m_ctx *m2m_ctx,
>  				       enum v4l2_buf_type type)
>  {
> @@ -229,14 +235,22 @@ EXPORT_SYMBOL_GPL(v4l2_m2m_buf_remove_by_idx);
>  void *v4l2_m2m_get_curr_priv(struct v4l2_m2m_dev *m2m_dev)
>  {
>  	unsigned long flags;
> -	void *ret = NULL;
> +	struct v4l2_m2m_ctx *first_ctx;
> 
>  	spin_lock_irqsave(&m2m_dev->job_spinlock, flags);
> -	if (m2m_dev->curr_ctx)
> -		ret = m2m_dev->curr_ctx->priv;
> +	if (list_empty(&m2m_dev->job_queue)) {
> +		spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
> +		return NULL;
> +	}
> +
> +	first_ctx = list_first_entry(&m2m_dev->job_queue,
> +				     struct v4l2_m2m_ctx, queue);
>  	spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
> 
> -	return ret;
> +	if (first_ctx->job_flags & TRANS_RUNNING)
> +		return first_ctx->priv;
> +	else
> +		return NULL;
>  }
>  EXPORT_SYMBOL(v4l2_m2m_get_curr_priv);
> 
> @@ -252,13 +266,11 @@ EXPORT_SYMBOL(v4l2_m2m_get_curr_priv);
>  static void v4l2_m2m_try_run(struct v4l2_m2m_dev *m2m_dev)
>  {
>  	unsigned long flags;
> +	struct v4l2_m2m_ctx *ctx;
> +	struct v4l2_m2m_ctx *chosen_ctx = NULL;
> +	u32 running_jobs = 0;
> 
>  	spin_lock_irqsave(&m2m_dev->job_spinlock, flags);
> -	if (NULL != m2m_dev->curr_ctx) {
> -		spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
> -		dprintk("Another instance is running, won't run 
now\n");
> -		return;
> -	}
> 
>  	if (list_empty(&m2m_dev->job_queue)) {
>  		spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
> @@ -272,13 +284,30 @@ static void v4l2_m2m_try_run(struct v4l2_m2m_dev
> *m2m_dev) return;
>  	}
> 
> -	m2m_dev->curr_ctx = list_first_entry(&m2m_dev->job_queue,
> -				   struct v4l2_m2m_ctx, queue);
> -	m2m_dev->curr_ctx->job_flags |= TRANS_RUNNING;
> +	list_for_each_entry(ctx, &m2m_dev->job_queue, queue) {
> +		if (!(ctx->job_flags & TRANS_RUNNING)) {
> +			chosen_ctx = ctx;
> +			break;
> +		}
> +
> +		running_jobs++;
> +	}
> +	if (running_jobs >= m2m_dev->max_parallel_jobs) {
> +		spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
> +		dprintk("Maximum number of parallel jobs reached\n");
> +		return;
> +	}
> +	if (!chosen_ctx) {
> +		spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
> +		dprintk("All jobs already running\n");
> +		return;
> +	}
> +
> +	chosen_ctx->job_flags |= TRANS_RUNNING;
>  	spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
> 
> -	dprintk("Running job on m2m_ctx: %p\n", m2m_dev->curr_ctx);
> -	m2m_dev->m2m_ops->device_run(m2m_dev->curr_ctx->priv);
> +	dprintk("Running job on m2m_ctx: %p\n", chosen_ctx);
> +	m2m_dev->m2m_ops->device_run(chosen_ctx->priv);
>  }
> 
>  /*
> @@ -469,15 +498,14 @@ static void v4l2_m2m_schedule_next_job(struct
> v4l2_m2m_dev *m2m_dev, static bool _v4l2_m2m_job_finish(struct v4l2_m2m_dev
> *m2m_dev,
>  				 struct v4l2_m2m_ctx *m2m_ctx)
>  {
> -	if (!m2m_dev->curr_ctx || m2m_dev->curr_ctx != m2m_ctx) {
> +	if (!m2m_ctx || !(m2m_ctx->job_flags & TRANS_RUNNING)) {
>  		dprintk("Called by an instance not currently 
running\n");
>  		return false;
>  	}
> 
> -	list_del(&m2m_dev->curr_ctx->queue);
> -	m2m_dev->curr_ctx->job_flags &= ~(TRANS_QUEUED | TRANS_RUNNING);
> -	wake_up(&m2m_dev->curr_ctx->finished);
> -	m2m_dev->curr_ctx = NULL;
> +	list_del(&m2m_ctx->queue);
> +	m2m_ctx->job_flags &= ~(TRANS_QUEUED | TRANS_RUNNING);
> +	wake_up(&m2m_ctx->finished);
>  	return true;
>  }
> 
> @@ -544,16 +572,19 @@ EXPORT_SYMBOL(v4l2_m2m_buf_done_and_job_finish);
>  void v4l2_m2m_suspend(struct v4l2_m2m_dev *m2m_dev)
>  {
>  	unsigned long flags;
> -	struct v4l2_m2m_ctx *curr_ctx;
> +	struct v4l2_m2m_ctx *ctx;
> +	struct v4l2_m2m_ctx *ctx_safe;
> 
>  	spin_lock_irqsave(&m2m_dev->job_spinlock, flags);
>  	m2m_dev->job_queue_flags |= QUEUE_PAUSED;
> -	curr_ctx = m2m_dev->curr_ctx;
>  	spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
> 
> -	if (curr_ctx)
> -		wait_event(curr_ctx->finished,
> -			   !(curr_ctx->job_flags & TRANS_RUNNING));
> +	list_for_each_entry_safe(ctx, ctx_safe, &m2m_dev->job_queue, queue) 
{
> +		if (!(ctx->job_flags & TRANS_RUNNING))
> +			break;
> +
> +		wait_event(ctx->finished, !(ctx->job_flags & 
TRANS_RUNNING));
> +	}
>  }
>  EXPORT_SYMBOL(v4l2_m2m_suspend);
> 
> @@ -896,10 +927,8 @@ int v4l2_m2m_streamoff(struct file *file, struct
> v4l2_m2m_ctx *m2m_ctx, q_ctx->num_rdy = 0;
>  	spin_unlock_irqrestore(&q_ctx->rdy_spinlock, flags);
> 
> -	if (m2m_dev->curr_ctx == m2m_ctx) {
> -		m2m_dev->curr_ctx = NULL;
> +	if (m2m_ctx->job_flags & TRANS_RUNNING)
>  		wake_up(&m2m_ctx->finished);
> -	}
>  	spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job);
> 
>  	return 0;
> @@ -1194,12 +1223,12 @@ struct v4l2_m2m_dev *v4l2_m2m_init(const struct
> v4l2_m2m_ops *m2m_ops) if (!m2m_dev)
>  		return ERR_PTR(-ENOMEM);
> 
> -	m2m_dev->curr_ctx = NULL;
>  	m2m_dev->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);
> +	m2m_dev->max_parallel_jobs = 1;
> 
>  	return m2m_dev;
>  }
> diff --git a/include/media/v4l2-mem2mem.h b/include/media/v4l2-mem2mem.h
> index 31de25d792b98..e6177d0eaf637 100644
> --- a/include/media/v4l2-mem2mem.h
> +++ b/include/media/v4l2-mem2mem.h
> @@ -594,6 +594,9 @@ static inline void v4l2_m2m_set_dst_buffered(struct
> v4l2_m2m_ctx *m2m_ctx, m2m_ctx->cap_q_ctx.buffered = buffered;
>  }
> 
> +void v4l2_m2m_set_max_parallel_jobs(struct v4l2_m2m_dev *m2m_dev,
> +				    u32 max_parallel_jobs);
> +
>  /**
>   * v4l2_m2m_ctx_release() - release m2m context
>   *