linux-kernel - Re: [RFC][PATCH 03/15] videobuf2: add V4L2_FLAG_MEMORY_NON

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Date:   Fri, 10 Jan 2020 18:46:07 +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: [RFC][PATCH 03/15] videobuf2: add
 V4L2_FLAG_MEMORY_NON_CONSISTENT flag

On (20/01/10 10:36), Hans Verkuil wrote:
[..]
> > diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
> > index 9149b57728e5..b08b5609f5f3 100644
> > --- a/Documentation/media/uapi/v4l/buffer.rst
> > +++ b/Documentation/media/uapi/v4l/buffer.rst
> > @@ -705,6 +705,25 @@ Buffer Flags
> >  
> >  .. c:type:: v4l2_memory
> >  
> > +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
> > +      - Set DMA_ATTR_NON_CONSISTENT queue memory consistency bit,
> > +	so all queue buffers may be allocated in non-consistent memory.
> 
> This needs much more extensive documentation. This is a userspace API,
> and it shouldn't refer to a kernelspace API. Instead, explain what it
> means from a user perspective. Also, how does this relate to the cache
> buffer flags?
> 
> These things are tricky, so it is worth spending some time on writing
> good documentation.

Agreed. I'll give it a shot, will try to improve it.

	-ss