CMA: document cma=0

It isn't obvious that CMA can be disabled on the kernel's command line, so
document it.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Chuck Ebbert <cebbert.lkml@gmail.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 5 insertions, 1 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a126a31dde02..809e880bc787 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -656,7 +656,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         Sets the size of kernel global memory area for
                         contiguous memory allocations and optionally the
                         placement constraint by the physical address range of
-                        memory allocations. For more information, see
+                        memory allocations. A value of 0 disables CMA
+                        altogether. For more information, see
                         include/linux/dma-contiguous.h
 
         cmo_free_hint=  [PPC] Format: { yes | no }
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 134f763d90fd..61a33f4ba608 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -252,6 +252,9 @@ config DMA_CMA
           to allocate big physically-contiguous blocks of memory for use with
           hardware components that do not support I/O map nor scatter-gather.
 
+          You can disable CMA by specifying "cma=0" on the kernel's command
+          line.
+
           For more information see <include/linux/dma-contiguous.h>.
           If unsure, say "n".