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@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/io.h b/include/linux/io.h
index 32403b5716e5b8c4a5eb21bfad1f2e4bf7604501..e2c8419278c192fd8002ae0b470ea2421dc51a57 100644 (file)
--- a/include/linux/io.h
+++ b/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 --git a/kernel/memremap.c b/kernel/memremap.c
index e5e685e6ff2adaa1a0ad27a81766f384cfa34b31..a6d382312e6f3ff2cdb0bb526f8bbd2978ebffc1 100644 (file)
--- 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);