ARM: dma: replace ISA_DMA_THRESHOLD with a variable

ISA_DMA_THRESHOLD has been unused by non-arch code, so lets now get
rid of it from ARM by replacing it with arm_dma_zone_mask.  Move
dma_supported() and dma_set_mask() out of line, and have
dma_supported() check this new variable instead.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/dma-mapping.c

@@ -25,9 +25,11 @@
 #include <asm/tlbflush.h>
 #include <asm/sizes.h>
 
+#include "mm.h"
+
 static u64 get_coherent_dma_mask(struct device *dev)
 {
-	u64 mask = ISA_DMA_THRESHOLD;
+	u64 mask = (u64)arm_dma_limit;
 
 	if (dev) {
 		mask = dev->coherent_dma_mask;
@@ -41,10 +43,10 @@ static u64 get_coherent_dma_mask(struct device *dev)
 			return 0;
 		}
 
-		if ((~mask) & ISA_DMA_THRESHOLD) {
+		if ((~mask) & (u64)arm_dma_limit) {
 			dev_warn(dev, "coherent DMA mask %#llx is smaller "
 				 "than system GFP_DMA mask %#llx\n",
-				 mask, (unsigned long long)ISA_DMA_THRESHOLD);
+				 mask, (u64)arm_dma_limit);
 			return 0;
 		}
 	}
@@ -657,6 +659,33 @@ void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
 }
 EXPORT_SYMBOL(dma_sync_sg_for_device);
 
+/*
+ * Return whether the given device DMA address mask can be supported
+ * properly.  For example, if your device can only drive the low 24-bits
+ * during bus mastering, then you would pass 0x00ffffff as the mask
+ * to this function.
+ */
+int dma_supported(struct device *dev, u64 mask)
+{
+	if (mask < (u64)arm_dma_limit)
+		return 0;
+	return 1;
+}
+EXPORT_SYMBOL(dma_supported);
+
+int dma_set_mask(struct device *dev, u64 dma_mask)
+{
+	if (!dev->dma_mask || !dma_supported(dev, dma_mask))
+		return -EIO;
+
+#ifndef CONFIG_DMABOUNCE
+	*dev->dma_mask = dma_mask;
+#endif
+
+	return 0;
+}
+EXPORT_SYMBOL(dma_set_mask);
+
 #define PREALLOC_DMA_DEBUG_ENTRIES	4096
 
 static int __init dma_debug_do_init(void)