bitops: Adjust the comment on get_order() to describe the size==0 case

Adjust the comment on get_order() to note that the result of passing a size of
0 results in an undefined value.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: http://lkml.kernel.org/r/20120220223917.16199.9416.stgit@warthog.procyon.org.uk
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 22 insertions, 1 deletions

diff --git a/include/asm-generic/getorder.h b/include/asm-generic/getorder.h
index 67e7245dc9b3..76e9687a3c86 100644
--- a/include/asm-generic/getorder.h
+++ b/include/asm-generic/getorder.h
@@ -5,7 +5,28 @@
 
 #include <linux/compiler.h>
 
-/* Pure 2^n version of get_order */
+/**
+ * get_order - Determine the allocation order of a memory size
+ * @size: The size for which to get the order
+ *
+ * Determine the allocation order of a particular sized block of memory.  This
+ * is on a logarithmic scale, where:
+ *
+ *      0 -> 2^0 * PAGE_SIZE and below
+ *      1 -> 2^1 * PAGE_SIZE to 2^0 * PAGE_SIZE + 1
+ *      2 -> 2^2 * PAGE_SIZE to 2^1 * PAGE_SIZE + 1
+ *      3 -> 2^3 * PAGE_SIZE to 2^2 * PAGE_SIZE + 1
+ *      4 -> 2^4 * PAGE_SIZE to 2^3 * PAGE_SIZE + 1
+ *      ...
+ *
+ * The order returned is used to find the smallest allocation granule required
+ * to hold an object of the specified size.
+ *
+ * The result is undefined if the size is 0.
+ *
+ * This function may be used to initialise variables with compile time
+ * evaluations of constants.
+ */
 static inline __attribute_const__ int get_order(unsigned long size)
 {
         int order;