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SubjectRe: [PATCHv3 03/11] videobuf2: add V4L2_FLAG_MEMORY_NON_CONSISTENT flag
On (20/02/27 13:25), Hans Verkuil wrote:
[..]
> > + - vb2 buffer is allocated either in consistent (it will be automatically
>
> vb2 -> A
>
> (vb2 is a kAPI term, and shouldn't be used in uAPI documentation)
>
> > + coherent between CPU and bus) or non-consistent memory. The latter
>
> CPU and bus -> the CPU and the bus
>
> > + can provide performance gains, for instance CPU cache sync/flush
>
> CPU -> the CPU
>
> > + operations can be avoided if the buffer is accessed by the corresponding
> > + device only and CPU does not read/write to/from that buffer. However,
>
> CPU -> the CPU
>
> > + this requires extra care from the driver -- it must guarantee memory
> > + consistency by issuing cache flush/sync when consistency is needed.
>
> cache -> a cache
>
> > + If this flag is set V4L2 will attempt to allocate vb2 buffer in
>
> vb2 -> the
>
> > + non-consistent memory. The flag takes effect only if the buffer is
> > + used for :ref:`memory mapping <mmap>` I/O and the queue reports
>
> reports -> reports the

OK.

> > +++ b/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> > @@ -156,6 +156,13 @@ aborting or finishing any DMA in progress, an implicit
> > - Only valid for stateless decoders. If set, then userspace can set the
> > ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag to hold off on returning the
> > capture buffer until the OUTPUT timestamp changes.
> > + * - ``V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS``
> > + - 0x00000040
> > + - Set when the queue/buffer support memory consistency and cache
>
> support -> supports

OK.

> > +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > @@ -711,6 +711,8 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
> > *caps |= V4L2_BUF_CAP_SUPPORTS_DMABUF;
> > if (q->subsystem_flags & VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF)
> > *caps |= V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF;
> > + if ((q->allow_cache_hints != 0) && (q->io_modes & VB2_MMAP))
>
> Just say:
>
> if (q->allow_cache_hints && (q->io_modes & VB2_MMAP))

OK.

-ss

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