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>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a126a31dde020c58395e073e630996422116b949..809e880bc78762c9b8a8f160ec0efb1a9a35e311 100644 (file)
--- 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 134f763d90fdaf36668198cf6ac3d0406c77efdc..61a33f4ba608cdc2fe01f691f46f92b2aba1d3e7 100644 (file)
--- 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".