linux-kernel - Re: [PATCH v6 03/14] videobuf2: handle V4L2 buffer cache flags

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Message-ID: <20200602101834.GA617@jagdpanzerIV.localdomain>
Date:   Tue, 2 Jun 2020 19:18:34 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tomasz Figa <tfiga@...omium.org>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v6 03/14] videobuf2: handle V4L2 buffer cache flags

Hi Hans,

On (20/06/02 11:51), Hans Verkuil wrote:
> Hi Sergey,
> 
> While doing final testing for this patch series (together with the v4l-utils patch)
> I found one remaining issue:

Thanks for the report.

> > +static void set_buffer_cache_hints(struct vb2_queue *q,
> > +				   struct vb2_buffer *vb,
> > +				   struct v4l2_buffer *b)
> > +{
> > +	/*
> > +	 * DMA exporter should take care of cache syncs, so we can avoid
> > +	 * explicit ->prepare()/->finish() syncs. For other ->memory types
> > +	 * we always need ->prepare() or/and ->finish() cache sync.
> > +	 */
> > +	if (q->memory == VB2_MEMORY_DMABUF) {
> > +		vb->need_cache_sync_on_finish = 0;
> > +		vb->need_cache_sync_on_prepare = 0;
> > +		return;
> > +	}
> > +
> > +	/*
> > +	 * Cache sync/invalidation flags are set by default in order to
> > +	 * preserve existing behaviour for old apps/drivers.
> > +	 */
> > +	vb->need_cache_sync_on_prepare = 1;
> > +	vb->need_cache_sync_on_finish = 1;
> > +
> > +	if (!vb2_queue_allows_cache_hints(q)) {
> > +		/*
> > +		 * Clear buffer cache flags if queue does not support user
> > +		 * space hints. That's to indicate to userspace that these
> > +		 * flags won't work.
> > +		 */
> > +		b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_INVALIDATE;
> > +		b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_CLEAN;
> > +		return;
> > +	}
> 
> These two flags need to be cleared for VB2_MEMORY_DMABUF as well in the test above.
> This bug is causing v4l2-compliance failures (use the test-media script in contrib/test
> in v4l-utils: 'sudo test-media vim2m').

Sorry, Hans, do you suggest to have something like this:

	if (q->memory == VB2_MEMORY_DMABUF) {
		vb->need_cache_sync_on_finish = 0;
		vb->need_cache_sync_on_prepare = 0;
		b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_INVALIDATE;
		b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_CLEAN;
		return;
	}

I didn't clear the ->flags there because we clear the vb flush/sync
flags: ->need_cache_sync_on_finish/prepare are zeros for DMABUF memory
type. Which is equivalent to passing V4L2_BUF_FLAG_NO_CACHE_INVALIDATE
V4L2_BUF_FLAG_NO_CACHE_CLEAN. IOW we would clearing both "vb's do cache
sync" and request's "do not cache sync".

> It's enough to post a v6.1 for this patch, everything else is fine.

Thanks!

	-ss