[PATCH] cma: debug: document new debugfs interface

[Sasha Levin <sasha.levin@oracle.com>]

Document the structure and files under the new debugfs interface.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 Documentation/cma/debugfs.txt |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
 create mode 100644 Documentation/cma/debugfs.txt

diff --git a/Documentation/cma/debugfs.txt b/Documentation/cma/debugfs.txt
new file mode 100644
index 0000000..6cef20a
--- /dev/null
+++ b/Documentation/cma/debugfs.txt
@@ -0,0 +1,21 @@
+The CMA debugfs interface is useful to retrieve basic information out of the
+different CMA areas and to test allocation/release in each of the areas.
+
+Each CMA zone represents a directory under <debugfs>/cma/, indexed by the
+kernel's CMA index. So the first CMA zone would be:
+
+	<debugfs>/cma/cma-0
+
+The structure of the files created under that directory is as follows:
+
+ - [RO] base_pfn: The base PFN (Page Frame Number) of the zone.
+ - [RO] count: Amount of memory in the CMA area.
+ - [RO] order_per_bit: Order of pages represented by one bit.
+ - [RO] bitmap: The bitmap of page states in the zone.
+ - [WO] alloc: Allocate N pages from that CMA area. For example:
+
+	echo 5 > <debugfs>/cma/cma-2/alloc
+
+would try to allocate 5 pages from the cma-2 area.
+
+ - [WO] free: Free N pages from that CMA area, similar to the above.
-- 
1.7.10.4

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