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Date:   Wed, 22 Jan 2020 12:48:26 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Hans Verkuil <hverkuil@xs4all.nl>
Cc:     Hans Verkuil <hans.verkuil@cisco.com>,
        Tomasz Figa <tfiga@chromium.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Sakari Ailus <sakari.ailus@iki.fi>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Pawel Osciak <posciak@chromium.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: Re: [RFC][PATCH 05/15] videobuf2: handle
 V4L2_FLAG_MEMORY_NON_CONSISTENT in REQBUFS
Message-ID: <20200122034826.GA49953@google.com>
References: <20191217032034.54897-1-senozhatsky@chromium.org>
 <20191217032034.54897-6-senozhatsky@chromium.org>
 <8d0c95c3-64a2-ec14-0ac2-204b0430b2b4@xs4all.nl>
 <20200122021805.GE149602@google.com>
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On (20/01/22 11:18), Sergey Senozhatsky wrote:
[..]
> > > +    * -
> > > +      - __u32
> > >        - ``reserved``\ [1]
> > >        - A place holder for future extensions. Drivers and applications
> > > -	must set the array to zero.
> > > +	must set the array to zero, unless application wants to specify
> > > +        buffer management ``flags``.
> > 
> > I think support for this flag should be signaled as a V4L2_BUF_CAP capability.
> > If the capability is not set, then vb2 should set 'flags' to 0 to preserve the
> > old 'Drivers and applications must set the array to zero' behavior.
> 
> The patch set adds V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS towards the end of the
> series, I guess I can shuffle the patches and change the wording here.

Or I can add separate queue flag and V4L2_BUF_CAP:

struct vb2_queue {
...
	allow_cache_hints:1
+	allow_consistency_hints:1
...
}

and then have CAP_SUPPORTS_CACHE_HINTS/CAP_SUPPORTS_CONSISTENCY_HINTS.

	-ss