linux-kernel - Re: [PATCHv4 01/11] videobuf2: add cache management members

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Message-ID: <20200309073909.GD46830@google.com>
Date:   Mon, 9 Mar 2020 16:39:09 +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,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCHv4 01/11] videobuf2: add cache management members

On (20/03/09 08:28), Hans Verkuil wrote:
> >>> I'm looking into it. Will it work if I patch the vivid test driver to
> >>> enable/disable ->allow_cache_hints bit per-node and include the patch
> >>> into the series. So then v4l2 tests can create some nodes with
> >>> ->allow_cache_hints.  Something like this:
> >>
> >> I would add a 'cache_hints' module parameter (array of bool) to tell vivid
> >> whether cache hints should be set or not for each instance. It would be useful
> >> to have this in vivid. Don't forget to update Documentation/media/v4l-drivers/vivid.rst
> >> as well.
> > 
> > I see. Hmm, how do I do "test that V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS
> > is never set" then?
> 
> Not sure I understand your question. When requesting buffers for non-MMAP memory,
> this capability must never be returned. That has nothing to do with a cache_hints
> module option.

OK. What I thought was that not every MMAP memory node can have cache
hints enabled, so it should be verified that only MMAP nodes which were
configured to allow_cache_hints should report that CAP, the rest of MMAP
nodes (if any) should have that CAP bit clear.

	-ss