[PATCH][RFC] arm: dma-mapping: Add support for allocating/mapping cached buffers

[Laura Abbott]

There are currently no dma allocation APIs that support cached
buffers. For some use cases, caching provides a signficiant
performance boost that beats write-combining regions. Add
apis to allocate and map a cached DMA region.

Signed-off-by: Laura Abbott <lauraa at codeaurora.org>
---
 arch/arm/include/asm/dma-mapping.h |   21 +++++++++++++++++++++
 arch/arm/mm/dma-mapping.c          |   21 +++++++++++++++++++++
 2 files changed, 42 insertions(+), 0 deletions(-)

diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
index dc988ff..1565403 100644
--- a/arch/arm/include/asm/dma-mapping.h
+++ b/arch/arm/include/asm/dma-mapping.h
@@ -239,12 +239,33 @@ int dma_mmap_coherent(struct device *, struct vm_area_struct *,
 extern void *dma_alloc_writecombine(struct device *, size_t, dma_addr_t *,
 		gfp_t);
 
+/**
+ * dma_alloc_cached - allocate cached memory for DMA
+ * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
+ * @size: required memory size
+ * @handle: bus-specific DMA address
+ *
+ * Allocate some cached memory for a device for
+ * performing DMA.  This function allocates pages, and will
+ * return the CPU-viewed address, and sets @handle to be the
+ * device-viewed address.
+ */
+extern void *dma_alloc_cached(struct device *, size_t, dma_addr_t *,
+		gfp_t);
+
 #define dma_free_writecombine(dev,size,cpu_addr,handle) \
 	dma_free_coherent(dev,size,cpu_addr,handle)
 
+#define dma_free_cached(dev,size,cpu_addr,handle) \
+	dma_free_coherent(dev,size,cpu_addr,handle)
+
 int dma_mmap_writecombine(struct device *, struct vm_area_struct *,
 		void *, dma_addr_t, size_t);
 
+
+int dma_mmap_cached(struct device *, struct vm_area_struct *,
+		void *, dma_addr_t, size_t);
+
 /*
  * This can be called during boot to increase the size of the consistent
  * DMA region above it's default value of 2MB. It must be called before the
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index b1911c4..f396ddc 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -633,6 +633,20 @@ dma_alloc_writecombine(struct device *dev, size_t size, dma_addr_t *handle, gfp_
 }
 EXPORT_SYMBOL(dma_alloc_writecombine);
 
+/*
+ * Allocate a cached DMA region
+ */
+void *
+dma_alloc_cached(struct device *dev, size_t size, dma_addr_t *handle, gfp_t gfp)
+{
+	return __dma_alloc(dev, size, handle, gfp,
+			   pgprot_kernel,
+			   __builtin_return_address(0));
+}
+EXPORT_SYMBOL(dma_alloc_cached);
+
+
+
 static int dma_mmap(struct device *dev, struct vm_area_struct *vma,
 		    void *cpu_addr, dma_addr_t dma_addr, size_t size)
 {
@@ -664,6 +678,13 @@ int dma_mmap_writecombine(struct device *dev, struct vm_area_struct *vma,
 }
 EXPORT_SYMBOL(dma_mmap_writecombine);
 
+int dma_mmap_cached(struct device *dev, struct vm_area_struct *vma,
+			  void *cpu_addr, dma_addr_t dma_addr, size_t size)
+{
+	return dma_mmap(dev, vma, cpu_addr, dma_addr, size);
+}
+EXPORT_SYMBOL(dma_mmap_cached);
+
 
 /*
  * Free a buffer as defined by the above mapping.
-- 
1.7.8.3