linux-kernel - [PATCH v6 11/14] videobuf2: add begin/end cpu

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Date:   Fri, 15 May 2020 01:01:50 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Hans Verkuil <hans.verkuil@...co.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tomasz Figa <tfiga@...omium.org>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH v6 11/14] videobuf2: add begin/end cpu_access callbacks to dma-sg

From: Sergey Senozhatsky <senozhatsky@...omium.org>

Provide begin_cpu_access() and end_cpu_access() dma_buf_ops
callbacks for cache synchronisation on exported buffers.

V4L2_FLAG_MEMORY_NON_CONSISTENT has no effect on dma-sg buffers.
dma-sg allocates memory using the page allocator directly, so
there is no memory consistency guarantee.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 .../media/common/videobuf2/videobuf2-dma-sg.c | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
index 92072a08af25..595137e358e7 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
@@ -120,6 +120,12 @@ static void *vb2_dma_sg_alloc(struct device *dev, unsigned long dma_attrs,
 	buf->num_pages = size >> PAGE_SHIFT;
 	buf->dma_sgt = &buf->sg_table;
 
+	/*
+	 * NOTE: dma-sg allocates memory using the page allocator directly, so
+	 * there is no memory consistency guarantee, hence dma-sg ignores DMA
+	 * attributes passed from the upper layer. That means that
+	 * V4L2_FLAG_MEMORY_NON_CONSISTENT has no effect on dma-sg buffers.
+	 */
 	buf->pages = kvmalloc_array(buf->num_pages, sizeof(struct page *),
 				    GFP_KERNEL | __GFP_ZERO);
 	if (!buf->pages)
@@ -469,6 +475,28 @@ static void vb2_dma_sg_dmabuf_ops_release(struct dma_buf *dbuf)
 	vb2_dma_sg_put(dbuf->priv);
 }
 
+static int
+vb2_dma_sg_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf,
+				       enum dma_data_direction direction)
+{
+	struct vb2_dma_sg_buf *buf = dbuf->priv;
+	struct sg_table *sgt = buf->dma_sgt;
+
+	dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
+	return 0;
+}
+
+static int
+vb2_dma_sg_dmabuf_ops_end_cpu_access(struct dma_buf *dbuf,
+				     enum dma_data_direction direction)
+{
+	struct vb2_dma_sg_buf *buf = dbuf->priv;
+	struct sg_table *sgt = buf->dma_sgt;
+
+	dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
+	return 0;
+}
+
 static void *vb2_dma_sg_dmabuf_ops_vmap(struct dma_buf *dbuf)
 {
 	struct vb2_dma_sg_buf *buf = dbuf->priv;
@@ -487,6 +515,8 @@ static const struct dma_buf_ops vb2_dma_sg_dmabuf_ops = {
 	.detach = vb2_dma_sg_dmabuf_ops_detach,
 	.map_dma_buf = vb2_dma_sg_dmabuf_ops_map,
 	.unmap_dma_buf = vb2_dma_sg_dmabuf_ops_unmap,
+	.begin_cpu_access = vb2_dma_sg_dmabuf_ops_begin_cpu_access,
+	.end_cpu_access = vb2_dma_sg_dmabuf_ops_end_cpu_access,
 	.vmap = vb2_dma_sg_dmabuf_ops_vmap,
 	.mmap = vb2_dma_sg_dmabuf_ops_mmap,
 	.release = vb2_dma_sg_dmabuf_ops_release,
-- 
2.26.2