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SubjectRe: [PATCHv3 03/11] videobuf2: add V4L2_FLAG_MEMORY_NON_CONSISTENT flag
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On 2/26/20 12:15 PM, Sergey Senozhatsky wrote:
> By setting or clearing V4L2_FLAG_MEMORY_NON_CONSISTENT flag
> user-space should be able to set or clear queue's NON_CONSISTENT
> ->dma_attrs. Queue's ->dma_attrs are passed to the underlying
> allocator in __vb2_buf_mem_alloc(), so thus user-space is able
> to request vb2 buffer's memory to be either consistent (coherent)
> or non-consistent.
>
> The patch set also adds a corresponding capability flag:
> fill_buf_caps() reports V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS when
> queue supports user-space cache management hints.
>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---
> Documentation/media/uapi/v4l/buffer.rst | 29 +++++++++++++++++++
> .../media/uapi/v4l/vidioc-reqbufs.rst | 7 +++++
> .../media/common/videobuf2/videobuf2-v4l2.c | 2 ++
> include/uapi/linux/videodev2.h | 3 ++
> 4 files changed, 41 insertions(+)
>
> diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
> index 3112300c2fa0..6b629ac59bf2 100644
> --- a/Documentation/media/uapi/v4l/buffer.rst
> +++ b/Documentation/media/uapi/v4l/buffer.rst
> @@ -681,6 +681,35 @@ Buffer Flags
>
> \normalsize
>
> +.. _memory-flags:
> +
> +Memory Consistency Flags
> +========================
> +
> +.. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}|
> +
> +.. cssclass:: longtable
> +
> +.. flat-table::
> + :header-rows: 0
> + :stub-columns: 0
> + :widths: 3 1 4
> +
> + * .. _`V4L2_FLAG_MEMORY_NON_CONSISTENT`:
> +
> + - ``V4L2_FLAG_MEMORY_NON_CONSISTENT``
> + - 0x00000001
> + - 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

> + :ref:`V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS` capability.
>
> .. c:type:: v4l2_memory
>
> diff --git a/Documentation/media/uapi/v4l/vidioc-reqbufs.rst b/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> index d0c643db477a..917df6fb6486 100644
> --- a/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> +++ 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

> + management hints. See :ref:`V4L2_FLAG_MEMORY_NON_CONSISTENT`,
> + :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE` and
> + :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN`.
> +
>
> Return Value
> ============
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 2a604bd7793a..f91cba37e223 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ 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))

Regards,

Hans

> + *caps |= V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS;
> #ifdef CONFIG_MEDIA_CONTROLLER_REQUEST_API
> if (q->supports_requests)
> *caps |= V4L2_BUF_CAP_SUPPORTS_REQUESTS;
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 5f9357dcb060..e92c29864730 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -189,6 +189,8 @@ enum v4l2_memory {
> V4L2_MEMORY_DMABUF = 4,
> };
>
> +#define V4L2_FLAG_MEMORY_NON_CONSISTENT (1 << 0)
> +
> /* see also http://vektor.theorem.ca/graphics/ycbcr/ */
> enum v4l2_colorspace {
> /*
> @@ -946,6 +948,7 @@ struct v4l2_requestbuffers {
> #define V4L2_BUF_CAP_SUPPORTS_REQUESTS (1 << 3)
> #define V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS (1 << 4)
> #define V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF (1 << 5)
> +#define V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS (1 << 6)
>
> /**
> * struct v4l2_plane - plane info for multi-planar buffers
>

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