Re: [RFC v5 09/11] [media] vb2: add infrastructure to support out-fences

[Alexandre Courbot <acourbot@chromium.org>]

On Thursday, November 16, 2017 2:10:55 AM JST, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.com>
>
> Add vb2_setup_out_fence() and the needed members to struct vb2_buffer.
>
> v3:
> 	- Do not hold yet another ref to the out_fence (Brian Starkey)
>
> v2:	- change it to reflect fd_install at DQEVENT
> 	- add fence context for out-fences
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
> ---
>  drivers/media/v4l2-core/videobuf2-core.c | 28 ++++++++++++++++++++++++++++
>  include/media/videobuf2-core.h           | 20 ++++++++++++++++++++
>  2 files changed, 48 insertions(+)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c 
> b/drivers/media/v4l2-core/videobuf2-core.c
> index 26de4c80717d..8b4f0e9bcb36 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -24,8 +24,10 @@
>  #include <linux/freezer.h>
>  #include <linux/kthread.h>
>  #include <linux/dma-fence-array.h>
> +#include <linux/sync_file.h>
>  
>  #include <media/videobuf2-core.h>
> +#include <media/videobuf2-fence.h>
>  #include <media/v4l2-mc.h>
>  
>  #include <trace/events/vb2.h>
> @@ -1320,6 +1322,32 @@ int vb2_core_prepare_buf(struct 
> vb2_queue *q, unsigned int index, void *pb)
>  }
>  EXPORT_SYMBOL_GPL(vb2_core_prepare_buf);
>  
> +int vb2_setup_out_fence(struct vb2_queue *q, unsigned int index)
> +{
> +	struct vb2_buffer *vb;
> +
> +	vb = q->bufs[index];
> +
> +	vb->out_fence_fd = get_unused_fd_flags(O_CLOEXEC);

out_fence_fd is allocated in this patch but not used anywhere for the 
moment.
For consistency, maybe move its allocation to the next patch, or move the 
call
to fd_install() here if that is possible? In both cases, the call to 
get_unused_fd() can be moved right before fd_install() so you don't need to
call put_unused_fd() in the error paths below.

... same thing for sync_file too. Maybe this patch can just be merged into
the next one? The current patch just creates an incomplete version of 
vb2_setup_out_fence() for which no user exist yet.

> +
> +	vb->out_fence = vb2_fence_alloc(q->out_fence_context);
> +	if (!vb->out_fence) {
> +		put_unused_fd(vb->out_fence_fd);
> +		return -ENOMEM;
> +	}
> +
> +	vb->sync_file = sync_file_create(vb->out_fence);
> +	if (!vb->sync_file) {
> +		put_unused_fd(vb->out_fence_fd);
> +		dma_fence_put(vb->out_fence);
> +		vb->out_fence = NULL;
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(vb2_setup_out_fence);
> +
>  /**
>   * vb2_start_streaming() - Attempt to start streaming.
>   * @q:		videobuf2 queue
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 5f48c7be7770..a9b0697bd782 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -259,6 +259,10 @@ struct vb2_buffer {
>  	 *			using the buffer (queueing to the driver)
>  	 * fence_cb:		fence callback information
>  	 * fence_cb_lock:	protect callback signal/remove
> +	 * out_fence_fd:	the out_fence_fd to be shared with userspace.
> +	 * out_fence:		the out-fence associated with the buffer once
> +	 *			it is queued to the driver.
> +	 * sync_file:		the sync file to wrap the out fence
>  	 */
>  	enum vb2_buffer_state	state;
>  
> @@ -269,6 +273,10 @@ struct vb2_buffer {
>  	struct dma_fence_cb	fence_cb;
>  	spinlock_t              fence_cb_lock;
>  
> +	int			out_fence_fd;
> +	struct dma_fence	*out_fence;
> +	struct sync_file	*sync_file;
> +
>  #ifdef CONFIG_VIDEO_ADV_DEBUG
>  	/*
>  	 * Counters for how often these buffer-related ops are
> @@ -514,6 +522,7 @@ struct vb2_buf_ops {
>   * @last_buffer_dequeued: used in poll() and DQBUF to 
> immediately return if the
>   *		last decoded buffer was already dequeued. Set for capture queues
>   *		when a buffer with the V4L2_BUF_FLAG_LAST is dequeued.
> + * @out_fence_context: the fence context for the out fences
>   * @last_fence:	last in-fence received. Used to keep ordering.
>   * @fileio:	file io emulator internal data, used only if emulator is active
>   * @threadio:	thread io internal data, used only if thread is active
> @@ -569,6 +578,7 @@ struct vb2_queue {
>  	unsigned int			copy_timestamp:1;
>  	unsigned int			last_buffer_dequeued:1;
>  
> +	u64				out_fence_context;
>  	struct dma_fence		*last_fence;
>  
>  	struct vb2_fileio_data		*fileio;
> @@ -740,6 +750,16 @@ int vb2_core_create_bufs(struct vb2_queue 
> *q, enum vb2_memory memory,
>  int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int 
> index, void *pb);
>  
>  /**
> + * vb2_setup_out_fence() - setup new out-fence
> + * @q:		The vb2_queue where to setup it
> + * @index:	index of the buffer
> + *
> + * Setup the file descriptor, the fence and the sync_file for the next
> + * buffer to be queued and add everything to the tail of the 
> q->out_fence_list.
> + */
> +int vb2_setup_out_fence(struct vb2_queue *q, unsigned int index);
> +
> +/**
>   * vb2_core_qbuf() - Queue a buffer from userspace
>   *
>   * @q:		videobuf2 queue