linux-kernel - Re: [PATCHv3 05/11] videobuf2: handle V4L2_FLAG_MEMORY_NON

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Message-ID: <20200228013820.GM122464@google.com>
Date:   Fri, 28 Feb 2020 10:38:20 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Sakari Ailus <sakari.ailus@....fi>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Pawel Osciak <posciak@...omium.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 05/11] videobuf2: handle
 V4L2_FLAG_MEMORY_NON_CONSISTENT flag

On (20/02/27 13:36), Hans Verkuil wrote:
> > diff --git a/Documentation/media/uapi/v4l/vidioc-create-bufs.rst b/Documentation/media/uapi/v4l/vidioc-create-bufs.rst
> > index bd08e4f77ae4..6a8a4d5de2f1 100644
> > --- a/Documentation/media/uapi/v4l/vidioc-create-bufs.rst
> > +++ b/Documentation/media/uapi/v4l/vidioc-create-bufs.rst
> > @@ -121,7 +121,13 @@ than the number requested.
> >  	other changes, then set ``count`` to 0, ``memory`` to
> >  	``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.
> >      * - __u32
> > -      - ``reserved``\ [7]
> > +      - ``flags``
> > +      - Specifies additional buffer management attributes.
> > +	See :ref:`memory-flags`. Old drivers and applications must set it to
> > +	zero.
> 
> Drop the last sentence, it's not relevant.

OK.

> > +
> > +    * - __u32
> > +      - ``reserved``\ [6]
> >        - A place holder for future extensions. Drivers and applications
> >  	must set the array to zero.
> 
> Old drivers and applications still think reserved is [7] and will zero this.

OK.

Hmm... If those apps use hard-coded size then we might have a problem.
If they use sizeof(reserved) then everything is OK. Shall we also have
a union here?

> > diff --git a/Documentation/media/uapi/v4l/vidioc-reqbufs.rst b/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> > index 917df6fb6486..e52cc4401fba 100644
> > --- a/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> > +++ b/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> > @@ -112,10 +112,19 @@ aborting or finishing any DMA in progress, an implicit
> >  	``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will
> >  	free any previously allocated buffers, so this is typically something
> >  	that will be done at the start of the application.
> > -    * - __u32
> > +    * - union
> > +      - (anonymous)
> 
> Anonymous unions are formatted a bit differently (I made a very recent patch
> that unified the union formatting in the v4l docs). See e.g.
> Documentation/media/uapi/v4l/vidioc-g-ext-ctrls.rst.

OK, will take a look.

	-ss