Re: [PATCH v6,04/24] v4l: add documentation for restricted memory flag

[Laurent Pinchart]

Hi Jefrey,

Thank you for the patch.

On Thu, May 16, 2024 at 08:20:42PM +0800, Yunfei Dong wrote:
> From: Jeffrey Kardatzke <jkardatzke@xxxxxxxxxx>
> 
> Adds documentation for V4L2_MEMORY_FLAG_RESTRICTED.
> 
> Signed-off-by: Jeffrey Kardatzke <jkardatzke@xxxxxxxxxx>
> Signed-off-by: Yunfei Dong <yunfei.dong@xxxxxxxxxxxx>
> ---
>  Documentation/userspace-api/media/v4l/buffer.rst | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst
> index 52bbee81c080..807e43bfed2b 100644
> --- a/Documentation/userspace-api/media/v4l/buffer.rst
> +++ b/Documentation/userspace-api/media/v4l/buffer.rst
> @@ -696,7 +696,7 @@ enum v4l2_memory
>  
>  .. _memory-flags:
>  
> -Memory Consistency Flags
> +Memory Flags
>  ------------------------
>  
>  .. raw:: latex
> @@ -728,6 +728,14 @@ Memory Consistency Flags
>  	only if the buffer is used for :ref:`memory mapping <mmap>` I/O and the
>  	queue reports the :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS
>  	<V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability.
> +    * .. _`V4L2-MEMORY-FLAG-RESTRICTED`:
> +
> +      - ``V4L2_MEMORY_FLAG_RESTRICTED``
> +      - 0x00000002
> +      - The queued buffers are expected to be in restricted memory. If not, an
> +	error will be returned. This flag can only be used with ``V4L2_MEMORY_DMABUF``.
> +	Typically restricted buffers are allocated using a restricted dma-heap. This flag
> +	can only be specified if the ``V4L2_BUF_CAP_SUPPORTS_RESTRICTED_MEM`` is set.

Why is this flag needed ? Given that the usage model requires the V4L2
device to be a dma buf importer, why would userspace set the
V4L2_BUF_CAP_SUPPORTS_RESTRICTED_MEM flag and pass a non-restricted
buffer to the device ?

The V4L2_BUF_CAP_SUPPORTS_RESTRICTED_MEM flag also needs to be
documented in the relevant section, I don't think that's done in this
series.

>  
>  .. raw:: latex
>  

-- 
Regards,

Laurent Pinchart