The patch titled
Subject: memremap: add MEMREMAP_WC flag
has been added to the -mm tree. Its filename is
memremap-add-memremap_wc-flag.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/memremap-add-memremap_wc-flag.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/memremap-add-memremap_wc-flag.patch
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------------------------------------------------------
From: Brian Starkey <brian.starkey@xxxxxxx>
Subject: memremap: add MEMREMAP_WC flag
Add a flag to memremap() for writecombine mappings. Mappings satisfied by
this flag will not be cached, however writes may be delayed or combined
into more efficient bursts. This is most suitable for buffers written
sequentially by the CPU for use by other DMA devices.
Signed-off-by: Brian Starkey <brian.starkey@xxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/io.h | 1 +
kernel/memremap.c | 13 +++++++++++--
2 files changed, 12 insertions(+), 2 deletions(-)
diff -puN include/linux/io.h~memremap-add-memremap_wc-flag include/linux/io.h
--- a/include/linux/io.h~memremap-add-memremap_wc-flag
+++ a/include/linux/io.h
@@ -135,6 +135,7 @@ enum {
/* See memremap() kernel-doc for usage description... */
MEMREMAP_WB = 1 << 0,
MEMREMAP_WT = 1 << 1,
+ MEMREMAP_WC = 1 << 2,
};
void *memremap(resource_size_t offset, size_t size, unsigned long flags);
diff -puN kernel/memremap.c~memremap-add-memremap_wc-flag kernel/memremap.c
--- a/kernel/memremap.c~memremap-add-memremap_wc-flag
+++ a/kernel/memremap.c
@@ -41,11 +41,13 @@ static void *try_ram_remap(resource_size
* memremap() - remap an iomem_resource as cacheable memory
* @offset: iomem resource start address
* @size: size of remap
- * @flags: either MEMREMAP_WB or MEMREMAP_WT
+ * @flags: any of MEMREMAP_WB, MEMREMAP_WT and MEMREMAP_WC
*
* memremap() is "ioremap" for cases where it is known that the resource
* being mapped does not have i/o side effects and the __iomem
- * annotation is not applicable.
+ * annotation is not applicable. In the case of multiple flags, the different
+ * mapping types will be attempted in the order listed below until one of
+ * them succeeds.
*
* MEMREMAP_WB - matches the default mapping for System RAM on
* the architecture. This is usually a read-allocate write-back cache.
@@ -57,6 +59,10 @@ static void *try_ram_remap(resource_size
* cache or are written through to memory and never exist in a
* cache-dirty state with respect to program visibility. Attempts to
* map System RAM with this mapping type will fail.
+ *
+ * MEMREMAP_WC - establish a writecombine mapping, whereby writes may
+ * be coalesced together (e.g. in the CPU's write buffers), but is otherwise
+ * uncached. Attempts to map System RAM with this mapping type will fail.
*/
void *memremap(resource_size_t offset, size_t size, unsigned long flags)
{
@@ -102,6 +108,9 @@ void *memremap(resource_size_t offset, s
if (!addr && (flags & MEMREMAP_WT))
addr = ioremap_wt(offset, size);
+ if (!addr && (flags & MEMREMAP_WC))
+ addr = ioremap_wc(offset, size);
+
return addr;
}
EXPORT_SYMBOL(memremap);
_
Patches currently in -mm which might be from brian.starkey@xxxxxxx are
memremap-dont-modify-flags.patch
memremap-add-memremap_wc-flag.patch
drivers-dma-coherent-use-memremap_wc-for-dma_memory_map.patch
drivers-dma-coherent-use-memset_io-for-dma_memory_io-mappings.patch
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