[PATCH 05/12] dma-buf: add explicit buffer pinning

[Christian König]

Add optional explicit pinning callbacks instead of implicitly assume the
exporter pins the buffer when a mapping is created.

Signed-off-by: Christian König <christian.koenig at amd.com>
---
 drivers/dma-buf/dma-buf.c | 39 +++++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h   | 37 +++++++++++++++++++++++++++++++------
 2 files changed, 70 insertions(+), 6 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index a3738fab3927..f23ff8355505 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -630,6 +630,41 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
 }
 EXPORT_SYMBOL_GPL(dma_buf_detach);
 
+/**
+ * dma_buf_pin - Lock down the DMA-buf
+ *
+ * @dmabuf:	[in]	DMA-buf to lock down.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure.
+ */
+int dma_buf_pin(struct dma_buf *dmabuf)
+{
+	int ret = 0;
+
+	reservation_object_assert_held(dmabuf->resv);
+
+	if (dmabuf->ops->pin)
+		ret = dmabuf->ops->pin(dmabuf);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dma_buf_pin);
+
+/**
+ * dma_buf_unpin - Remove lock from DMA-buf
+ *
+ * @dmabuf:	[in]	DMA-buf to unlock.
+ */
+void dma_buf_unpin(struct dma_buf *dmabuf)
+{
+	reservation_object_assert_held(dmabuf->resv);
+
+	if (dmabuf->ops->unpin)
+		dmabuf->ops->unpin(dmabuf);
+}
+EXPORT_SYMBOL_GPL(dma_buf_unpin);
+
 /**
  * dma_buf_map_attachment_locked - Maps the buffer into _device_ address space
  * with the reservation lock held. Is a wrapper for map_dma_buf() of the
@@ -666,6 +701,8 @@ dma_buf_map_attachment_locked(struct dma_buf_attachment *attach,
 	 */
 	if (attach->invalidate)
 		list_del(&attach->node);
+	else
+		dma_buf_pin(attach->dmabuf);
 	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
 	if (attach->invalidate)
 		list_add(&attach->node, &attach->dmabuf->attachments);
@@ -735,6 +772,8 @@ void dma_buf_unmap_attachment_locked(struct dma_buf_attachment *attach,
 
 	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
 						direction);
+	if (!attach->invalidate)
+		dma_buf_unpin(attach->dmabuf);
 }
 EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment_locked);
 
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index ece4638359a8..a615b74e5894 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -100,14 +100,40 @@ struct dma_buf_ops {
 	 */
 	void (*detach)(struct dma_buf *, struct dma_buf_attachment *);
 
+	/**
+	 * @pin_dma_buf:
+	 *
+	 * This is called by dma_buf_pin and lets the exporter know that an
+	 * importer assumes that the DMA-buf can't be invalidated any more.
+	 *
+	 * This is called with the dmabuf->resv object locked.
+	 *
+	 * This callback is optional.
+	 *
+	 * Returns:
+	 *
+	 * 0 on success, negative error code on failure.
+	 */
+	int (*pin)(struct dma_buf *);
+
+	/**
+	 * @unpin_dma_buf:
+	 *
+	 * This is called by dma_buf_unpin and lets the exporter know that an
+	 * importer doesn't need to the DMA-buf to stay were it is any more.
+	 *
+	 * This is called with the dmabuf->resv object locked.
+	 *
+	 * This callback is optional.
+	 */
+	void (*unpin)(struct dma_buf *);
+
 	/**
 	 * @map_dma_buf:
 	 *
 	 * This is called by dma_buf_map_attachment() and is used to map a
 	 * shared &dma_buf into device address space, and it is mandatory. It
-	 * can only be called if @attach has been called successfully. This
-	 * essentially pins the DMA buffer into place, and it cannot be moved
-	 * any more
+	 * can only be called if @attach has been called successfully.
 	 *
 	 * This call may sleep, e.g. when the backing storage first needs to be
 	 * allocated, or moved to a location suitable for all currently attached
@@ -148,9 +174,6 @@ struct dma_buf_ops {
 	 *
 	 * This is called by dma_buf_unmap_attachment() and should unmap and
 	 * release the &sg_table allocated in @map_dma_buf, and it is mandatory.
-	 * It should also unpin the backing storage if this is the last mapping
-	 * of the DMA buffer, it the exporter supports backing storage
-	 * migration.
 	 *
 	 * This is always called with the dmabuf->resv object locked when
 	 * no_sgt_cache is true.
@@ -442,6 +465,8 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
 struct dma_buf *dma_buf_get(int fd);
 void dma_buf_put(struct dma_buf *dmabuf);
 
+int dma_buf_pin(struct dma_buf *dmabuf);
+void dma_buf_unpin(struct dma_buf *dmabuf);
 struct sg_table *dma_buf_map_attachment_locked(struct dma_buf_attachment *,
 					       enum dma_data_direction);
 struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
-- 
2.17.1