[PATCH] dma-buf: add initial vmap documentation

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 Documentation/dma-buf-sharing.txt |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index 3bbd5c5..98e9fa0 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -300,6 +300,17 @@ Access to a dma_buf from the kernel context involves three steps:
    Note that these calls need to always succeed. The exporter needs to complete
    any preparations that might fail in begin_cpu_access.
 
+   For some circumstances the overhead of kmap can be too high, a vmap interface
+   is introduced. This interface shouldn't be used very carefully, as vmalloc
+   space is a limited resources on many architectures.
+
+   Interfaces:
+      void *dma_buf_vmap(struct dma_buf *dmabuf)
+      void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
+
+   This 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.
+
 3. Finish access
 
    When the importer is done accessing the range specified in begin_cpu_access,
-- 
1.7.6