Re: [PATCH 1/7 v2] media: vb2: add bidirectional flag in vb2_queue

[Hans Verkuil]

On 08/21/2017 11:29 AM, Marek Szyprowski wrote:
> Hi Stanimir,
> 
> On 2017-08-21 11:09, 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>
> 
> This has been already discussed about a year ago, but it got lost in
> meantime, probably due to lack of users. I hope that this time it
> finally will get into vb2.
> 
> For the reference, see https://patchwork.kernel.org/patch/9388163/

Interesting.

Stanimir, I like your implementation better than the macro in the old
patch. But as it said there, videobuf2-dma-sg/contig/vmalloc.c have references
to DMA_FROM_DEVICE that won't work with BIDIRECTIONAL, so those need
to be adapted as well. I missed that when I reviewed your patch :-(

Regards,

	Hans

> 
>> ---
>> v2: move dma_dir into private section.
>>
>>   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..ef9b64398c8c 100644
>> --- a/include/media/videobuf2-core.h
>> +++ b/include/media/videobuf2-core.h
>> @@ -427,6 +427,16 @@ 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.
>> + * @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
>> @@ -465,6 +475,7 @@ struct vb2_buf_ops {
>>    * Private elements (won't appear at the uAPI book):
>>    * @mmap_lock:	private mutex used when buffers are allocated/freed/mmapped
>>    * @memory:	current memory type used
>> + * @dma_dir:	DMA mapping direction.
>>    * @bufs:	videobuf buffer structures
>>    * @num_buffers: number of allocated/used buffers
>>    * @queued_list: list of buffers currently queued from userspace
>> @@ -495,6 +506,7 @@ struct vb2_queue {
>>   	unsigned int			io_modes;
>>   	struct device			*dev;
>>   	unsigned long			dma_attrs;
>> +	unsigned			bidirectional:1;
>>   	unsigned			fileio_read_once:1;
>>   	unsigned			fileio_write_immediately:1;
>>   	unsigned			allow_zero_bytesused:1;
>> @@ -516,6 +528,7 @@ struct vb2_queue {
>>   	/* private: internal use only */
>>   	struct mutex			mmap_lock;
>>   	unsigned int			memory;
>> +	enum dma_data_direction		dma_dir;
>>   	struct vb2_buffer		*bufs[VB2_MAX_FRAME];
>>   	unsigned int			num_buffers;
>>   
> 
> Best regards
>