linux-kernel - Re: [RFC][PATCHv2 02/12] videobuf2: handle V4L2 buffer cache flags

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Message-ID: <20200205081350.GK41358@google.com>
Date:   Wed, 5 Feb 2020 17:13:50 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
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][PATCHv2 02/12] videobuf2: handle V4L2 buffer cache flags

On (20/02/04 11:56), Sergey Senozhatsky wrote:
> +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;
> +	}
> +
> +	if (!q->allow_cache_hints)
> +		return;
> +
> +	vb->need_cache_sync_on_prepare = 1;
> +	/*
> +	 * ->finish() cache sync can be avoided when queue direction is
> +	 * TO_DEVICE.
> +	 */
> +	if (q->dma_dir != DMA_TO_DEVICE)
> +		vb->need_cache_sync_on_finish = 1;
> +	else
> +		vb->need_cache_sync_on_finish = 0;
> +
> +	if (b->flags & V4L2_BUF_FLAG_NO_CACHE_INVALIDATE)
> +		vb->need_cache_sync_on_finish = 0;
> +
> +	if (b->flags & V4L2_BUF_FLAG_NO_CACHE_CLEAN)
> +		vb->need_cache_sync_on_prepare = 0;
> +}

Last minute changes (tm), sorry. This is not right.


====8<====8<====

From: Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH] videobuf2: handle V4L2 buffer cache flags

Set video buffer cache management flags corresponding to V4L2 cache
flags.

Both ->prepare() and ->finish() cache management hints should be
passed during this stage (buffer preparation), because there is no
other way for user-space to skip ->finish() cache flush.

There are two possible alternative approaches:
- The first one is to move cache sync from ->finish() to dqbuf().
  But this breaks some drivers, that need to fix-up buffers before
  dequeueing them.

- The second one is to move ->finish() call from ->done() to dqbuf.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 .../media/common/videobuf2/videobuf2-v4l2.c   | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index eb5d5db96552..8ef57496b34a 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -337,6 +337,41 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
 	return 0;
 }
 
+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;
+	}
+
+	vb->need_cache_sync_on_prepare = 1;
+	vb->need_cache_sync_on_finish = 1;
+
+	if (!q->allow_cache_hints)
+		return;
+
+	/*
+	 * ->finish() cache sync can be avoided when queue direction is
+	 * TO_DEVICE.
+	 */
+	if (q->dma_dir == DMA_TO_DEVICE)
+		vb->need_cache_sync_on_finish = 0;
+
+	if (b->flags & V4L2_BUF_FLAG_NO_CACHE_INVALIDATE)
+		vb->need_cache_sync_on_finish = 0;
+
+	if (b->flags & V4L2_BUF_FLAG_NO_CACHE_CLEAN)
+		vb->need_cache_sync_on_prepare = 0;
+}
+
 static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
 				    struct v4l2_buffer *b, bool is_prepare,
 				    struct media_request **p_req)
@@ -381,6 +416,7 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *md
 	}
 
 	if (!vb->prepared) {
+		set_buffer_cache_hints(q, vb, b);
 		/* Copy relevant information provided by the userspace */
 		memset(vbuf->planes, 0,
 		       sizeof(vbuf->planes[0]) * vb->num_planes);
-- 
2.25.0.341.g760bfbb309-goog