diff options
| author | Christoph Hellwig <hch@lst.de> | 2020-09-11 10:56:52 +0200 |
|---|---|---|
| committer | Christoph Hellwig <hch@lst.de> | 2020-10-06 07:07:04 +0200 |
| commit | 0b1abd1fb7efafc25231c54a67c6fbb3d3127efd (patch) | |
| tree | 1a3bd0b8188be13aa6294e14b3d54922fd88dbac /kernel/dma/contiguous.c | |
| parent | 580a0cc9c3f662e0b10136bc8af1e672e472806f (diff) | |
dma-mapping: merge <linux/dma-contiguous.h> into <linux/dma-map-ops.h>
Merge dma-contiguous.h into dma-map-ops.h, after removing the comment
describing the contiguous allocator into kernel/dma/contigous.c.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Diffstat (limited to 'kernel/dma/contiguous.c')
| -rw-r--r-- | kernel/dma/contiguous.c | 30 |
1 files changed, 29 insertions, 1 deletions
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c index bf05ec2256e1..6bfb763fff6f 100644 --- a/kernel/dma/contiguous.c +++ b/kernel/dma/contiguous.c @@ -5,6 +5,34 @@ * Written by: * Marek Szyprowski <m.szyprowski@samsung.com> * Michal Nazarewicz <mina86@mina86.com> + * + * Contiguous Memory Allocator + * + * The Contiguous Memory Allocator (CMA) makes it possible to + * allocate big contiguous chunks of memory after the system has + * booted. + * + * Why is it needed? + * + * Various devices on embedded systems have no scatter-getter and/or + * IO map support and require contiguous blocks of memory to + * operate. They include devices such as cameras, hardware video + * coders, etc. + * + * Such devices often require big memory buffers (a full HD frame + * is, for instance, more then 2 mega pixels large, i.e. more than 6 + * MB of memory), which makes mechanisms such as kmalloc() or + * alloc_page() ineffective. + * + * At the same time, a solution where a big memory region is + * reserved for a device is suboptimal since often more memory is + * reserved then strictly required and, moreover, the memory is + * inaccessible to page system even if device drivers don't use it. + * + * CMA tries to solve this issue by operating on memory regions + * where only movable pages can be allocated from. This way, kernel + * can use the memory for pagecache and when device driver requests + * it, allocated pages can be migrated. */ #define pr_fmt(fmt) "cma: " fmt @@ -21,7 +49,7 @@ #include <linux/memblock.h> #include <linux/err.h> #include <linux/sizes.h> -#include <linux/dma-contiguous.h> +#include <linux/dma-map-ops.h> #include <linux/cma.h> #ifdef CONFIG_CMA_SIZE_MBYTES |