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Subject: Re: [RFC][PATCH 05/15] videobuf2: handle
 V4L2_FLAG_MEMORY_NON_CONSISTENT in REQBUFS
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
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
References: <20191217032034.54897-1-senozhatsky@chromium.org>
 <20191217032034.54897-6-senozhatsky@chromium.org>
 <8d0c95c3-64a2-ec14-0ac2-204b0430b2b4@xs4all.nl>
 <20200122021805.GE149602@google.com> <20200122034826.GA49953@google.com>
From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <7c4accc6-56f2-ecd0-1549-a4114b339ce8@xs4all.nl>
Date:   Thu, 23 Jan 2020 12:08:34 +0100
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On 1/22/20 4:48 AM, Sergey Senozhatsky wrote:
> 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.

Don't these two go hand-in-hand? I.e. either neither are supported, or
both are supported? If so, then one queue flag is sufficient.

Regards,

	Hans

> 
> 	-ss
>