From c907e0eb43a522de60fb651c011c553f87273222 Mon Sep 17 00:00:00 2001 From: Brian Starkey Date: Tue, 22 Mar 2016 14:28:00 -0700 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 Reviewed-by: Catalin Marinas Cc: Dan Williams Cc: Greg Kroah-Hartman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/memremap.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) (limited to 'kernel/memremap.c') diff --git a/kernel/memremap.c b/kernel/memremap.c index e5e685e6ff2a..a6d382312e6f 100644 --- a/kernel/memremap.c +++ b/kernel/memremap.c @@ -41,11 +41,13 @@ static void *try_ram_remap(resource_size_t offset, size_t 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_t offset, size_t 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, size_t size, unsigned long flags) 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); -- cgit