linux-kernel - Re: [PATCH v3,1/2] media: v4l UAPI: add V4L2_BUF_CAP_SUPPORTS_RO

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Message-ID: <047b49b0-53d4-3ddf-e629-1686a6d4eb31@xs4all.nl>
Date:   Thu, 23 Jul 2020 10:10:35 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Yunfei Dong <yunfei.dong@...iatek.com>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Tomasz Figa <tfiga@...omium.org>,
        Alexandre Courbot <acourbot@...omium.org>
Subject: Re: [PATCH v3,1/2] media: v4l UAPI: add
 V4L2_BUF_CAP_SUPPORTS_RO_REQUESTS

On 01/07/2020 11:35, Yunfei Dong wrote:
> This patch adds support for the V4L2_BUF_CAP_SUPPORTS_RO_REQUESTS
> flag. This flag is used for Read-only(Ro) Request.
> 
> Signed-off-by: Yunfei Dong <yunfei.dong@...iatek.com>
> ---
>  Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> index b6d52083707b..7c7451773b8e 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> @@ -126,6 +126,7 @@ aborting or finishing any DMA in progress, an implicit
>  .. _V4L2-BUF-CAP-SUPPORTS-REQUESTS:
>  .. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS:
>  .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF:
> +.. _V4L2-BUF-CAP-SUPPORTS-RO-REQUESTS:
>  
>  .. cssclass:: longtable
>  
> @@ -156,6 +157,9 @@ 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_RO_REQUESTS``
> +      - 0x00000040
> +      - This buffer type supports :ref:`requests <media-request-api>`.

This is wrong, it supports *read-only* requests.

Also, Documentation/userspace-api/media/mediactl/request-api.rst should mention
read-only requests: I think a new section "Read-Only Requests" explaining the
purpose and use of such requests would be best. It can be inserted just before
the "Example for a Codec Device" at the end.

Regards,

	Hans

>  
>  Return Value
>  ============
>