Messages in this thread | | | Subject | Re: [PATCH 2/2] [media] vb2: Add support for use_dma_bidirectional queue flag | From | Thierry Escande <> | Date | Tue, 18 Oct 2016 18:08:53 +0200 |
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Hi Sakari,
On 17/10/2016 12:06, Sakari Ailus wrote: > Hi Thierry, > > Thanks for the set. A few comments below. > > On Fri, Oct 14, 2016 at 02:08:14PM +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. > > Just out of curiosity --- when do you return these buffers back to the user? > Once they're no longer needed as reference frames? Tbh, I don't now. This is used by a rockchip vpu driver not yet upstreamed in the chromeos v4.4 kernel tree. Pawel might answer this question I guess.
> >> >> 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> >> Reviewed-by: Tomasz Figa <tfiga@chromium.org> >> Signed-off-by: Thierry Escande <thierry.escande@collabora.com> >> --- >> drivers/media/v4l2-core/videobuf2-v4l2.c | 8 ++++++-- >> include/media/videobuf2-core.h | 4 ++++ >> 2 files changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c >> index fde1e2d..9255291 100644 >> --- a/drivers/media/v4l2-core/videobuf2-v4l2.c >> +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c >> @@ -659,8 +659,12 @@ int vb2_queue_init(struct vb2_queue *q) >> * queues will always initialize waiting_for_buffers to false. >> */ >> q->quirk_poll_must_check_waiting_for_buffers = true; >> - q->dma_dir = V4L2_TYPE_IS_OUTPUT(q->type) >> - ? DMA_TO_DEVICE : DMA_FROM_DEVICE; >> + >> + if (V4L2_TYPE_IS_OUTPUT(q->type)) >> + q->dma_dir = DMA_TO_DEVICE; >> + else >> + q->dma_dir = q->use_dma_bidirectional >> + ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE; >> >> return vb2_core_queue_init(q); >> } >> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h >> index 38410dd..e613c74 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. >> + * @use_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 >> @@ -500,6 +503,7 @@ struct vb2_queue { >> unsigned fileio_write_immediately:1; >> unsigned allow_zero_bytesused:1; >> unsigned quirk_poll_must_check_waiting_for_buffers:1; >> + unsigned use_dma_bidirectional:1; > > This field is in the same struct as dma_dir which it directly affects. > > How about adding a macro instead to give you the queue DMA direction > instead? > > E.g. > > #define vb2_dma_dir(q) \ > (V4L2_TYPE_IS_OUTPUT((q)->type) ? DMA_TO_DEVICE : \ > (q)->use_dma_bidirectional ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE) > > I would call this capture_dma_bidirectional as it only affects capture. Or > simply choose DMA_BIDIRECTIONAL whenever the flag is set. Sure. Will do.
Regards, Thierry
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