[PATCHv3 1/1] staging/ion: Add support to get ion handle from dma buf

[Rohit kumar <rohit.kr@samsung.com>]

Currently we can only import dma buf fd's to get ion_handle.
Adding support to import dma buf handles to support kernel
specific use cases.

An example use case is in linux platforms such as Tizen, in which
DRM-GEM is used for buffer management for graphics. It has gem_handle
corresponding to a buffer and uses gem_name for sharing the buffer
with other processes. However,it also uses dma_buf fd for 3d operations.
For wayland, there are multiple calls for gem_handle to dma_buf fd
conversion. So, we store dma_buf associated with buffer. But, there is
no api for getting ion_handle from dma_buf. This patch exposes api to
retrieve the ion handle from dma_buf for similar use cases. With this
patch, we can integrate ION within DRM-GEM for buffer management and
dma_buf sharing.

Signed-off-by: Rohit kumar <rohit.kr@samsung.com>
---
v2: Updated commit message with use case explanation, as suggested by
    Laura Abbott<labbott@redhat.com>
v3: Fixed dmabuf refcount issue in ion_import_dma_buf. dma_buf_put()
    was being called without dma_buf_get(), so moving it to
    ion_import_dma_buf_fd().

 drivers/staging/android/ion/ion.c |   26 ++++++++++++++++++--------
 drivers/staging/android/ion/ion.h |   20 ++++++++++++++++----
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index e237e9f..7e86e18 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -1151,22 +1151,18 @@ int ion_share_dma_buf_fd(struct ion_client *client, struct ion_handle *handle)
 }
 EXPORT_SYMBOL(ion_share_dma_buf_fd);
 
-struct ion_handle *ion_import_dma_buf(struct ion_client *client, int fd)
+struct ion_handle *ion_import_dma_buf(struct ion_client *client,
+				      struct dma_buf *dmabuf)
 {
-	struct dma_buf *dmabuf;
 	struct ion_buffer *buffer;
 	struct ion_handle *handle;
 	int ret;
 
-	dmabuf = dma_buf_get(fd);
-	if (IS_ERR(dmabuf))
-		return ERR_CAST(dmabuf);
 	/* if this memory came from ion */
 
 	if (dmabuf->ops != &dma_buf_ops) {
 		pr_err("%s: can not import dmabuf from another exporter\n",
 		       __func__);
-		dma_buf_put(dmabuf);
 		return ERR_PTR(-EINVAL);
 	}
 	buffer = dmabuf->priv;
@@ -1194,11 +1190,25 @@ struct ion_handle *ion_import_dma_buf(struct ion_client *client, int fd)
 	}
 
 end:
-	dma_buf_put(dmabuf);
 	return handle;
 }
 EXPORT_SYMBOL(ion_import_dma_buf);
 
+struct ion_handle *ion_import_dma_buf_fd(struct ion_client *client, int fd)
+{
+	struct dma_buf *dmabuf;
+	struct ion_handle *handle;
+
+	dmabuf = dma_buf_get(fd);
+	if (IS_ERR(dmabuf))
+		return ERR_CAST(dmabuf);
+
+	handle = ion_import_dma_buf(client, dmabuf);
+	dma_buf_put(dmabuf);
+	return handle;
+}
+EXPORT_SYMBOL(ion_import_dma_buf_fd);
+
 static int ion_sync_for_device(struct ion_client *client, int fd)
 {
 	struct dma_buf *dmabuf;
@@ -1306,7 +1316,7 @@ static long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	{
 		struct ion_handle *handle;
 
-		handle = ion_import_dma_buf(client, data.fd.fd);
+		handle = ion_import_dma_buf_fd(client, data.fd.fd);
 		if (IS_ERR(handle))
 			ret = PTR_ERR(handle);
 		else
diff --git a/drivers/staging/android/ion/ion.h b/drivers/staging/android/ion/ion.h
index b860c5f..a1331fc 100644
--- a/drivers/staging/android/ion/ion.h
+++ b/drivers/staging/android/ion/ion.h
@@ -192,14 +192,26 @@ struct dma_buf *ion_share_dma_buf(struct ion_client *client,
 int ion_share_dma_buf_fd(struct ion_client *client, struct ion_handle *handle);
 
 /**
- * ion_import_dma_buf() - given an dma-buf fd from the ion exporter get handle
+ * ion_import_dma_buf() - get ion_handle from dma-buf
+ * @client:	the client
+ * @dmabuf:	the dma-buf
+ *
+ * Get the ion_buffer associated with the dma-buf and return the ion_handle.
+ * If no ion_handle exists for this buffer, return newly created ion_handle.
+ * If dma-buf from another exporter is passed, return ERR_PTR(-EINVAL)
+ */
+struct ion_handle *ion_import_dma_buf(struct ion_client *client,
+				      struct dma_buf *dmabuf);
+
+/**
+ * ion_import_dma_buf_fd() - given a dma-buf fd from the ion exporter get handle
  * @client:	the client
  * @fd:		the dma-buf fd
  *
- * Given an dma-buf fd that was allocated through ion via ion_share_dma_buf,
- * import that fd and return a handle representing it.  If a dma-buf from
+ * Given an dma-buf fd that was allocated through ion via ion_share_dma_buf_fd,
+ * import that fd and return a handle representing it. If a dma-buf from
  * another exporter is passed in this function will return ERR_PTR(-EINVAL)
  */
-struct ion_handle *ion_import_dma_buf(struct ion_client *client, int fd);
+struct ion_handle *ion_import_dma_buf_fd(struct ion_client *client, int fd);
 
 #endif /* _LINUX_ION_H */
-- 
1.7.9.5