[ARM] Extend DMA API on ARM for DMA-able writecombining memory.

This is mainly for ARM framebuffer drivers, some of which are
presently either open-coding this functionality, or using some
internal ARM architecture function to get what they want.

arch/arm/mm/consistent.c

@@ -226,6 +226,20 @@ dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *handle, int gfp)
 }
 EXPORT_SYMBOL(dma_alloc_coherent);
 
+/*
+ * Allocate a writecombining region, in much the same way as
+ * dma_alloc_coherent above.
+ */
+void *
+dma_alloc_writecombine(struct device *dev, size_t size, dma_addr_t *handle, int gfp)
+{
+	if (dev == NULL || *dev->dma_mask != 0xffffffff)
+		gfp |= GFP_DMA;
+
+	return consistent_alloc(gfp, size, handle, PTE_BUFFERABLE);
+}
+EXPORT_SYMBOL(dma_alloc_writecombine);
+
 /*
  * free a page as defined by the above mapping.
  */

include/asm-arm/dma-mapping.h

@@ -106,6 +106,23 @@ dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
 	consistent_free(cpu_addr, size, handle);
 }
 
+/**
+ * dma_alloc_writecombine - allocate writecombining 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 uncached, buffered 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_writecombine(struct device *dev, size_t size, dma_addr_t *handle, int gfp);
+
+#define dma_free_writecombine(dev,size,cpu_addr,handle) \
+	dma_free_coherent(dev,size,cpu_addr,handle)
+
 /**
  * dma_map_single - map a single buffer for streaming DMA
  * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices