Re: [PATCH 1/7] media: vb2: add bidirectional flag in vb2_queue

[Hans Verkuil]

On 08/18/17 16:16, Stanimir Varbanov wrote:
> This change is intended to give to the v4l2 drivers a choice to
> change the default behavior of the v4l2-core DMA mapping direction
> from DMA_TO/FROM_DEVICE (depending on the buffer type CAPTURE or
> OUTPUT) to DMA_BIDIRECTIONAL during queue_init time.
> 
> Initially the issue with DMA mapping direction has been found in
> Venus encoder driver where the hardware (firmware side) adds few
> lines padding on bottom of the image buffer, and the consequence
> is triggering of IOMMU protection faults.
> 
> This will help supporting venus encoder (and probably other drivers
> in the future) which wants to map output type of buffers as
> read/write.
> 
> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx>
> ---
>  drivers/media/v4l2-core/videobuf2-core.c | 17 ++++++++---------
>  include/media/videobuf2-core.h           | 13 +++++++++++++
>  2 files changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 0924594989b4..cb115ba6a1d2 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -194,8 +194,6 @@ 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;
>  	void *mem_priv;
>  	int plane;
>  	int ret = -ENOMEM;
> @@ -209,7 +207,7 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
>  
>  		mem_priv = call_ptr_memop(vb, alloc,
>  				q->alloc_devs[plane] ? : q->dev,
> -				q->dma_attrs, size, dma_dir, q->gfp_flags);
> +				q->dma_attrs, size, q->dma_dir, q->gfp_flags);
>  		if (IS_ERR_OR_NULL(mem_priv)) {
>  			if (mem_priv)
>  				ret = PTR_ERR(mem_priv);
> @@ -978,8 +976,6 @@ static int __prepare_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;
>  	bool reacquired = vb->planes[0].mem_priv == NULL;
>  
>  	memset(planes, 0, sizeof(planes[0]) * vb->num_planes);
> @@ -1030,7 +1026,7 @@ static int __prepare_userptr(struct vb2_buffer *vb, const void *pb)
>  		mem_priv = call_ptr_memop(vb, get_userptr,
>  				q->alloc_devs[plane] ? : q->dev,
>  				planes[plane].m.userptr,
> -				planes[plane].length, dma_dir);
> +				planes[plane].length, q->dma_dir);
>  		if (IS_ERR(mem_priv)) {
>  			dprintk(1, "failed acquiring userspace memory for plane %d\n",
>  				plane);
> @@ -1096,8 +1092,6 @@ static int __prepare_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;
>  	bool reacquired = vb->planes[0].mem_priv == NULL;
>  
>  	memset(planes, 0, sizeof(planes[0]) * vb->num_planes);
> @@ -1156,7 +1150,7 @@ static int __prepare_dmabuf(struct vb2_buffer *vb, const void *pb)
>  		/* Acquire each plane's memory */
>  		mem_priv = call_ptr_memop(vb, attach_dmabuf,
>  				q->alloc_devs[plane] ? : q->dev,
> -				dbuf, planes[plane].length, dma_dir);
> +				dbuf, planes[plane].length, q->dma_dir);
>  		if (IS_ERR(mem_priv)) {
>  			dprintk(1, "failed to attach dmabuf\n");
>  			ret = PTR_ERR(mem_priv);
> @@ -2003,6 +1997,11 @@ int vb2_core_queue_init(struct vb2_queue *q)
>  	if (q->buf_struct_size == 0)
>  		q->buf_struct_size = sizeof(struct vb2_buffer);
>  
> +	if (q->bidirectional)
> +		q->dma_dir = DMA_BIDIRECTIONAL;
> +	else
> +		q->dma_dir = q->is_output ? DMA_TO_DEVICE : DMA_FROM_DEVICE;
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(vb2_core_queue_init);
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index cb97c224be73..ede09fff1de8 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -427,6 +427,17 @@ struct vb2_buf_ops {
>   * @dev:	device to use for the default allocation context if the driver
>   *		doesn't fill in the @alloc_devs array.
>   * @dma_attrs:	DMA attributes to use for the DMA.
> + * @dma_dir:	DMA mapping direction.

This one should be moved to the 'Private elements' section. This is set and used
by the vb2 core, drivers won't set this.

Looks good otherwise.

Regards,

	Hans

> + * @bidirectional: when this flag is set the DMA direction for the buffers of
> + *		this queue will be overridden with DMA_BIDIRECTIONAL direction.
> + *		This is useful in cases where the hardware (firmware) writes to
> + *		a buffer which is mapped as read (DMA_TO_DEVICE), or reads from
> + *		buffer which is mapped for write (DMA_FROM_DEVICE) in order
> + *		to satisfy some internal hardware restrictions or adds a padding
> + *		needed by the processing algorithm. In case the DMA mapping is
> + *		not bidirectional but the hardware (firmware) trying to access
> + *		the buffer (in the opposite direction) this could lead to an
> + *		IOMMU protection faults.
>   * @fileio_read_once:		report EOF after reading the first buffer
>   * @fileio_write_immediately:	queue buffer after each write() call
>   * @allow_zero_bytesused:	allow bytesused == 0 to be passed to the driver
> @@ -495,6 +506,8 @@ struct vb2_queue {
>  	unsigned int			io_modes;
>  	struct device			*dev;
>  	unsigned long			dma_attrs;
> +	enum dma_data_direction		dma_dir;
> +	unsigned			bidirectional:1;
>  	unsigned			fileio_read_once:1;
>  	unsigned			fileio_write_immediately:1;
>  	unsigned			allow_zero_bytesused:1;
>