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

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Message-ID: <20240522111622.GA31185@pendragon.ideasonboard.com>
Date: Wed, 22 May 2024 14:16:22 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Yunfei Dong <yunfei.dong@...iatek.com>
Cc: Jeffrey Kardatzke <jkardatzke@...gle.com>,
	Nícolas F . R . A . Prado <nfraprado@...labora.com>,
	Nathan Hebert <nhebert@...omium.org>,
	Nicolas Dufresne <nicolas.dufresne@...labora.com>,
	Hans Verkuil <hverkuil-cisco@...all.nl>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Benjamin Gaignard <benjamin.gaignard@...labora.com>,
	Sebastian Fricke <sebastian.fricke@...labora.com>,
	Tomasz Figa <tfiga@...omium.org>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Chen-Yu Tsai <wenst@...omium.org>, Yong Wu <yong.wu@...iatek.com>,
	Hsin-Yi Wang <hsinyi@...omium.org>,
	Fritz Koenig <frkoenig@...omium.org>,
	Daniel Vetter <daniel@...ll.ch>, Steve Cho <stevecho@...omium.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Brian Starkey <Brian.Starkey@....com>,
	John Stultz <jstultz@...gle.com>,
	"T . J . Mercier" <tjmercier@...gle.com>,
	Christian König <christian.koenig@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v6,04/24] v4l: add documentation for restricted memory
 flag

Hi Jefrey,

Thank you for the patch.

On Thu, May 16, 2024 at 08:20:42PM +0800, Yunfei Dong wrote:
> From: Jeffrey Kardatzke <jkardatzke@...gle.com>
> 
> Adds documentation for V4L2_MEMORY_FLAG_RESTRICTED.
> 
> Signed-off-by: Jeffrey Kardatzke <jkardatzke@...gle.com>
> Signed-off-by: Yunfei Dong <yunfei.dong@...iatek.com>
> ---
>  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