Diffstat (limited to 'Documentation/dma-buf-sharing.txt')
1 files changed, 5 insertions, 1 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index 0188903bc9e..4966b1be42a 100644
@@ -302,7 +302,11 @@ Access to a dma_buf from the kernel context involves three steps:
void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
The vmap call can fail if there is no vmap support in the exporter, or if it
- runs out of vmalloc space. Fallback to kmap should be implemented.
+ runs out of vmalloc space. Fallback to kmap should be implemented. Note that
+ the dma-buf layer keeps a reference count for all vmap access and calls down
+ into the exporter's vmap function only when no vmapping exists, and only
+ unmaps it once. Protection against concurrent vmap/vunmap calls is provided
+ by taking the dma_buf->lock mutex.
3. Finish access