Re: [PATCH v3] [media] vb2: Add support for capture_dma_bidirectional queue flag

[Sakari Ailus <sakari.ailus@iki.fi>]

Hi Thierry,

On Thu, Oct 20, 2016 at 10:56:04AM +0200, Thierry Escande wrote:
> From: Pawel Osciak <posciak@chromium.org>
> 
> When this flag is set for CAPTURE queues by the driver on calling
> vb2_queue_init(), it forces the buffers on the queue to be
> allocated/mapped with DMA_BIDIRECTIONAL direction flag instead of
> DMA_FROM_DEVICE. This allows the device not only to write to the
> buffers, but also read out from them. This may be useful e.g. for codec
> hardware which may be using CAPTURE buffers as reference to decode
> other buffers.
> 
> This flag is ignored for OUTPUT queues as we don't want to allow HW to
> be able to write to OUTPUT buffers.
> 
> Signed-off-by: Pawel Osciak <posciak@chromium.org>
> Tested-by: Pawel Osciak <posciak@chromium.org>
> Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
> ---
> 
> Changes since v1:
> - Renamed use_dma_bidirectional field as capture_dma_bidirectional
> - Added a VB2_DMA_DIR() macro
> 
> Changes since v2:
> - Get rid of dma_dir field and therefore squashed the previous patch
> 
>  drivers/media/v4l2-core/videobuf2-core.c |  9 +++------
>  include/media/videobuf2-core.h           | 15 +++++++++++++++
>  2 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 21900202..22d6105 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -194,8 +194,7 @@ static void __enqueue_in_driver(struct vb2_buffer *vb);
>  static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
>  {
>  	struct vb2_queue *q = vb->vb2_queue;
> -	enum dma_data_direction dma_dir =
> -		q->is_output ? DMA_TO_DEVICE : DMA_FROM_DEVICE;
> +	enum dma_data_direction dma_dir = VB2_DMA_DIR(q);
>  	void *mem_priv;
>  	int plane;
>  	int ret = -ENOMEM;
> @@ -978,8 +977,7 @@ static int __qbuf_userptr(struct vb2_buffer *vb, const void *pb)
>  	void *mem_priv;
>  	unsigned int plane;
>  	int ret = 0;
> -	enum dma_data_direction dma_dir =
> -		q->is_output ? DMA_TO_DEVICE : DMA_FROM_DEVICE;
> +	enum dma_data_direction dma_dir = VB2_DMA_DIR(q);
>  	bool reacquired = vb->planes[0].mem_priv == NULL;
>  
>  	memset(planes, 0, sizeof(planes[0]) * vb->num_planes);
> @@ -1096,8 +1094,7 @@ static int __qbuf_dmabuf(struct vb2_buffer *vb, const void *pb)
>  	void *mem_priv;
>  	unsigned int plane;
>  	int ret = 0;
> -	enum dma_data_direction dma_dir =
> -		q->is_output ? DMA_TO_DEVICE : DMA_FROM_DEVICE;
> +	enum dma_data_direction dma_dir = VB2_DMA_DIR(q);
>  	bool reacquired = vb->planes[0].mem_priv == NULL;
>  
>  	memset(planes, 0, sizeof(planes[0]) * vb->num_planes);
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index ac5898a..631f08b 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -433,6 +433,9 @@ struct vb2_buf_ops {
>   * @quirk_poll_must_check_waiting_for_buffers: Return POLLERR at poll when QBUF
>   *              has not been called. This is a vb1 idiom that has been adopted
>   *              also by vb2.
> + * @capture_dma_bidirectional:	use DMA_BIDIRECTIONAL for CAPTURE buffers; this
> + *				allows HW to read from the CAPTURE buffers in
> + *				addition to writing; ignored for OUTPUT queues.
>   * @lock:	pointer to a mutex that protects the vb2_queue struct. The
>   *		driver can set this to a mutex to let the v4l2 core serialize
>   *		the queuing ioctls. If the driver wants to handle locking
> @@ -499,6 +502,7 @@ struct vb2_queue {
>  	unsigned			fileio_write_immediately:1;
>  	unsigned			allow_zero_bytesused:1;
>  	unsigned		   quirk_poll_must_check_waiting_for_buffers:1;
> +	unsigned			capture_dma_bidirectional:1;
>  
>  	struct mutex			*lock;
>  	void				*owner;
> @@ -554,6 +558,17 @@ struct vb2_queue {
>  #endif
>  };
>  
> +/*
> + * Return the corresponding DMA direction given the vb2_queue type (capture or
> + * output). returns DMA_BIRECTIONAL for capture buffers if the vb2_queue field

DMA_BIDIRECTIONAL

With that fixed,

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>

> + * capture_dma_bidirectional is set by the driver.
> + */
> +#define VB2_DMA_DIR(q) (V4L2_TYPE_IS_OUTPUT((q)->type)   \
> +			? DMA_TO_DEVICE                  \
> +			: (q)->capture_dma_bidirectional \
> +			  ? DMA_BIDIRECTIONAL            \
> +			  : DMA_FROM_DEVICE)
> +
>  /**
>   * vb2_plane_vaddr() - Return a kernel virtual address of a given plane
>   * @vb:		vb2_buffer to which the plane in question belongs to

-- 
Sakari Ailus
e-mail: sakari.ailus@iki.fi	XMPP: sailus@retiisi.org.uk