Blackfin arch: enable a choice to provide 4M DMA memory

support two cascaded AD73322 cards, more uncached DMA
memory is needed, so add a choice to provide 4M DMA memory
Signed-off-by: NCliff Cai <cliff.cai@analog.com>
Signed-off-by: NBryan Wu <cooloney@kernel.org>

arch/blackfin/Kconfig

@@ -685,6 +685,8 @@ choice
 	prompt "Uncached SDRAM region"
 	default DMA_UNCACHED_1M
 	depends on BFIN_DMA_5XX
+config DMA_UNCACHED_4M
+	bool "Enable 4M DMA region"
 config DMA_UNCACHED_2M
 	bool "Enable 2M DMA region"
 config DMA_UNCACHED_1M

include/asm-blackfin/bfin-global.h

@@ -37,7 +37,9 @@
 #include <linux/linkage.h>
 #include <linux/types.h>
 
-#if defined(CONFIG_DMA_UNCACHED_2M)
+#if defined(CONFIG_DMA_UNCACHED_4M)
+# define DMA_UNCACHED_REGION (4 * 1024 * 1024)
+#elif defined(CONFIG_DMA_UNCACHED_2M)
 # define DMA_UNCACHED_REGION (2 * 1024 * 1024)
 #elif defined(CONFIG_DMA_UNCACHED_1M)
 # define DMA_UNCACHED_REGION (1024 * 1024)