On 08/14/17 10:41, Stanimir Varbanov wrote:
> Hi,
>
> This RFC patch is intended to give to the 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 firmware side of the driver adds few
> lines padding on bottom of the image buffer, and the consequence was
> triggering of IOMMU protection faults.
>
> Probably other drivers could also has a benefit of this feature (hint)
> in the future.
>
> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx>
> ---
> drivers/media/v4l2-core/videobuf2-core.c | 3 +++
> include/media/videobuf2-core.h | 11 +++++++++++
> 2 files changed, 14 insertions(+)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 14f83cecfa92..17d07fda4cdc 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -200,6 +200,9 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
> int plane;
> int ret = -ENOMEM;
>
> + if (q->bidirectional)
> + dma_dir = DMA_BIDIRECTIONAL;
> +
Does this only have to be used in mem_alloc? In the __prepare_*() it is still using
DMA_TO/FROM_DEVICE.
I don't know enough of the low-level handling to be able to tell whether that is
a problem or not, but even if it is not then a comment somewhere to explain that
it is OK is probably a good idea.
Regards,
Hans
> /*
> * Allocate memory for all planes in this buffer
> * NOTE: mmapped areas should be page aligned
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index cb97c224be73..0b6e88e1aa79 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
> @@ -495,6 +505,7 @@ 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;
>
