[PATCH v5 1/6] dma-buf: Add dma_buf_{begin,end}_access()

[Paul Cercueil]

These functions should be used by device drivers when they start and
stop accessing the data of DMABUF. It allows DMABUF importers to cache
the dma_buf_attachment while ensuring that the data they want to access
is available for their device when the DMA transfers take place.

Signed-off-by: Paul Cercueil <paul at crapouillou.net>

---
v5: New patch
---
 drivers/dma-buf/dma-buf.c | 66 +++++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h   | 37 ++++++++++++++++++++++
 2 files changed, 103 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 8fe5aa67b167..a8bab6c18fcd 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -830,6 +830,8 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
  *     - dma_buf_mmap()
  *     - dma_buf_begin_cpu_access()
  *     - dma_buf_end_cpu_access()
+ *     - dma_buf_begin_access()
+ *     - dma_buf_end_access()
  *     - dma_buf_map_attachment_unlocked()
  *     - dma_buf_unmap_attachment_unlocked()
  *     - dma_buf_vmap_unlocked()
@@ -1602,6 +1604,70 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)
 }
 EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap_unlocked, DMA_BUF);
 
+/**
+ * @dma_buf_begin_access - Call before any hardware access from/to the DMABUF
+ * @attach:	[in]	attachment used for hardware access
+ * @sg_table:	[in]	scatterlist used for the DMA transfer
+ * @direction:  [in]    direction of DMA transfer
+ */
+int dma_buf_begin_access(struct dma_buf_attachment *attach,
+			 struct sg_table *sgt, enum dma_data_direction dir)
+{
+	struct dma_buf *dmabuf;
+	bool cookie;
+	int ret;
+
+	if (WARN_ON(!attach))
+		return -EINVAL;
+
+	dmabuf = attach->dmabuf;
+
+	if (!dmabuf->ops->begin_access)
+		return 0;
+
+	cookie = dma_fence_begin_signalling();
+	ret = dmabuf->ops->begin_access(attach, sgt, dir);
+	dma_fence_end_signalling(cookie);
+
+	if (WARN_ON_ONCE(ret))
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_begin_access, DMA_BUF);
+
+/**
+ * @dma_buf_end_access - Call after any hardware access from/to the DMABUF
+ * @attach:	[in]	attachment used for hardware access
+ * @sg_table:	[in]	scatterlist used for the DMA transfer
+ * @direction:  [in]    direction of DMA transfer
+ */
+int dma_buf_end_access(struct dma_buf_attachment *attach,
+		       struct sg_table *sgt, enum dma_data_direction dir)
+{
+	struct dma_buf *dmabuf;
+	bool cookie;
+	int ret;
+
+	if (WARN_ON(!attach))
+		return -EINVAL;
+
+	dmabuf = attach->dmabuf;
+
+	if (!dmabuf->ops->end_access)
+		return 0;
+
+	cookie = dma_fence_begin_signalling();
+	ret = dmabuf->ops->end_access(attach, sgt, dir);
+	dma_fence_end_signalling(cookie);
+
+	if (WARN_ON_ONCE(ret))
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_end_access, DMA_BUF);
+
 #ifdef CONFIG_DEBUG_FS
 static int dma_buf_debug_show(struct seq_file *s, void *unused)
 {
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 8ff4add71f88..8ba612c7cc16 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -246,6 +246,38 @@ struct dma_buf_ops {
 	 */
 	int (*end_cpu_access)(struct dma_buf *, enum dma_data_direction);
 
+	/**
+	 * @begin_access:
+	 *
+	 * This is called from dma_buf_begin_access() when a device driver
+	 * wants to access the data of the DMABUF. The exporter can use this
+	 * to flush/sync the caches if needed.
+	 *
+	 * This callback is optional.
+	 *
+	 * Returns:
+	 *
+	 * 0 on success or a negative error code on failure.
+	 */
+	int (*begin_access)(struct dma_buf_attachment *, struct sg_table *,
+			    enum dma_data_direction);
+
+	/**
+	 * @end_access:
+	 *
+	 * This is called from dma_buf_end_access() when a device driver is
+	 * done accessing the data of the DMABUF. The exporter can use this
+	 * to flush/sync the caches if needed.
+	 *
+	 * This callback is optional.
+	 *
+	 * Returns:
+	 *
+	 * 0 on success or a negative error code on failure.
+	 */
+	int (*end_access)(struct dma_buf_attachment *, struct sg_table *,
+			  enum dma_data_direction);
+
 	/**
 	 * @mmap:
 	 *
@@ -606,6 +638,11 @@ void dma_buf_detach(struct dma_buf *dmabuf,
 int dma_buf_pin(struct dma_buf_attachment *attach);
 void dma_buf_unpin(struct dma_buf_attachment *attach);
 
+int dma_buf_begin_access(struct dma_buf_attachment *attach,
+			 struct sg_table *sgt, enum dma_data_direction dir);
+int dma_buf_end_access(struct dma_buf_attachment *attach,
+		       struct sg_table *sgt, enum dma_data_direction dir);
+
 struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info);
 
 int dma_buf_fd(struct dma_buf *dmabuf, int flags);
-- 
2.43.0