nios2: add dma_alloc_coherent

This function return cache-line aligned allocation which is mapped
to uncached io region.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: Scott McNutt <smcnutt@psyent.com>

arch/nios2/include/asm/dma-mapping.h

+#ifndef __ASM_NIOS2_DMA_MAPPING_H
+#define __ASM_NIOS2_DMA_MAPPING_H
+
+/* dma_alloc_coherent() return cache-line aligned allocation which is mapped
+ * to uncached io region.
+ *
+ * IO_REGION_BASE should be defined in board config header file
+ *   0x80000000 for nommu, 0xe0000000 for mmu
+ */
+
+static inline void *dma_alloc_coherent(size_t len, unsigned long *handle)
+{
+	void *addr = malloc(len + CONFIG_SYS_DCACHELINE_SIZE);
+	if (!addr)
+		return 0;
+	flush_dcache((unsigned long)addr, len + CONFIG_SYS_DCACHELINE_SIZE);
+	*handle = ((unsigned long)addr +
+		   (CONFIG_SYS_DCACHELINE_SIZE - 1)) &
+		~(CONFIG_SYS_DCACHELINE_SIZE - 1) & ~(IO_REGION_BASE);
+	return (void *)(*handle | IO_REGION_BASE);
+}
+
+#endif /* __ASM_NIOS2_DMA_MAPPING_H */