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Subject: Re: [RFC][PATCHv2 05/12] videobuf2: handle
 V4L2_FLAG_MEMORY_NON_CONSISTENT flag
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: <20200204025641.218376-1-senozhatsky@chromium.org>
 <20200204025641.218376-6-senozhatsky@chromium.org>
 <83147032-25a4-9450-d455-437e82e09dc8@xs4all.nl>
 <20200219090547.GF122464@google.com>
From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <9bd88d23-9c4f-05dd-2514-b7c46f03a578@xs4all.nl>
Date:   Wed, 19 Feb 2020 10:11:39 +0100
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On 2/19/20 10:05 AM, Sergey Senozhatsky wrote:
> On (20/02/19 09:48), Hans Verkuil wrote:
> [..]
>>>  int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
>>>  {
>>>  	int ret = vb2_verify_memory_type(q, req->memory, req->type);
>>> +	bool consistent = true;
>>> +
>>> +	if (req->flags & V4L2_FLAG_MEMORY_NON_CONSISTENT)
>>> +		consistent = false;
>>
>> There is no check against allow_cache_hints: if that's 0, then
>> the V4L2_FLAG_MEMORY_NON_CONSISTENT flag should be cleared since it is
>> not supported.
> 
> The check is in set_queue_consistency()

That's the check against the functionality. I'm talking about the API level:
if !q->allow_cache_hints, then clear V4L2_FLAG_MEMORY_NON_CONSISTENT from
req->flags so that, when the ioctl returns to userspace, the application can
tell that that flag was rejected.

Regards,

	Hans

> 
> static void set_queue_consistency(struct vb2_queue *q, bool consistent_mem)
> {
> 	if (!q->allow_cache_hints)
> 		return;
> 
> 	if (consistent_mem)
> 		q->dma_attrs &= ~DMA_ATTR_NON_CONSISTENT;
> 	else
> 		q->dma_attrs |= DMA_ATTR_NON_CONSISTENT;
> }
> 
> I don't explicitly clear DMA_ATTR_NON_CONSISTENT attr for
> !->allow_cache_hints queues just in case if the driver for
> some reason sets that flag. ->allow_cache_hints is, thus,
> only for cases when user-space asks us to set or clear it.
> 
> 	-ss
>