linux-kernel - Re: [RFC][PATCH 05/15] videobuf2: handle V4L2_FLAG_MEMORY_NON

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Message-ID: <7c4accc6-56f2-ecd0-1549-a4114b339ce8@xs4all.nl>
Date:   Thu, 23 Jan 2020 12:08:34 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     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 05/15] videobuf2: handle
 V4L2_FLAG_MEMORY_NON_CONSISTENT in REQBUFS

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
>