linux-kernel - Re: [RFC][PATCHv2 05/12] videobuf2: handle V4L2_FLAG_MEMORY_NON

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Message-ID: <20200219090547.GF122464@google.com>
Date:   Wed, 19 Feb 2020 18:05:47 +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
Subject: Re: [RFC][PATCHv2 05/12] videobuf2: handle
 V4L2_FLAG_MEMORY_NON_CONSISTENT flag

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()

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