linux-kernel - Re: [RFC][PATCH 13/15] videobuf2: do not sync buffers for DMABUF queues

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Message-ID: <20200124073250.GA100275@google.com>
Date:   Fri, 24 Jan 2020 16:32:50 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Hans Verkuil <hverkuil@...all.nl>
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,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [RFC][PATCH 13/15] videobuf2: do not sync buffers for DMABUF
 queues

On (20/01/24 11:25), Sergey Senozhatsky wrote:
[..]
>
> > Then, if q->allow_cache_hint is set, then default to a cache sync (cache clean)
> > in the prepare for OUTPUT buffers and a cache sync (cache invalidate) in the
> > finish for CAPTURE buffers.
>
> We alter default cache sync behaviour based both on queue ->memory
> type and queue ->dma_dir. Shall both of those cases depend on
> ->allow_cache_hints, or q->memory can be independent?
>
> static void set_buffer_cache_hints(struct vb2_queue *q,
> 				   struct vb2_buffer *vb,
> 				   struct v4l2_buffer *b)
> {
> 	if (!q->allow_cache_hints)
> 		return;
>
> 	/*
> 	 * 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;
> 	}

I personally would prefer this to be above ->allow_cache_hints check,
IOW to be independent. Because we need to skip flush/invalidation for
DMABUF anyway, that's what allocators do in ->prepare() and ->finish()
currently.

	-ss