ARM: another fix for the DMA mapping checks

Peter reports that OMAP audio broke with the recent fix for these
checks, caused by OMAP audio using a 64-bit DMA mask.  We should
allow 64-bit DMA masks even with 32-bit dma_addr_t if we can be sure
the amount of RAM we have won't allow the 32-bit dma_addr_t to
overflow.  Unfortunately, the checks to detect overflow were not
correct.
Tested-by: NPeter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/dma-mapping.c

@@ -158,52 +158,62 @@ struct dma_map_ops arm_coherent_dma_ops = {
 };
 EXPORT_SYMBOL(arm_coherent_dma_ops);
 
-static u64 get_coherent_dma_mask(struct device *dev)
+static int __dma_supported(struct device *dev, u64 mask, bool warn)
 {
-	u64 mask = (u64)DMA_BIT_MASK(32);
-
-	if (dev) {
 	unsigned long max_dma_pfn;
 
-		mask = dev->coherent_dma_mask;
-
-		/*
-		 * Sanity check the DMA mask - it must be non-zero, and
-		 * must be able to be satisfied by a DMA allocation.
-		 */
-		if (mask == 0) {
-			dev_warn(dev, "coherent DMA mask is unset\n");
-			return 0;
-		}
-
-		max_dma_pfn = min(max_pfn, arm_dma_pfn_limit);
-
 	/*
 	 * If the mask allows for more memory than we can address,
-		 * and we actually have that much memory, then fail the
-		 * allocation.
+	 * and we actually have that much memory, then we must
+	 * indicate that DMA to this device is not supported.
 	 */
 	if (sizeof(mask) != sizeof(dma_addr_t) &&
 	    mask > (dma_addr_t)~0 &&
-		    dma_to_pfn(dev, ~0) > max_dma_pfn) {
+	    dma_to_pfn(dev, ~0) < max_pfn) {
+		if (warn) {
 			dev_warn(dev, "Coherent DMA mask %#llx is larger than dma_addr_t allows\n",
 				 mask);
 			dev_warn(dev, "Driver did not use or check the return value from dma_set_coherent_mask()?\n");
+		}
 		return 0;
 	}
 
+	max_dma_pfn = min(max_pfn, arm_dma_pfn_limit);
+
 	/*
-		 * Now check that the mask, when translated to a PFN,
-		 * fits within the allowable addresses which we can
-		 * allocate.
+	 * Translate the device's DMA mask to a PFN limit.  This
+	 * PFN number includes the page which we can DMA to.
 	 */
 	if (dma_to_pfn(dev, mask) < max_dma_pfn) {
+		if (warn)
 			dev_warn(dev, "Coherent DMA mask %#llx (pfn %#lx-%#lx) covers a smaller range of system memory than the DMA zone pfn 0x0-%#lx\n",
 				 mask,
 				 dma_to_pfn(dev, 0), dma_to_pfn(dev, mask) + 1,
-				 arm_dma_pfn_limit + 1);
+				 max_dma_pfn + 1);
 		return 0;
 	}
+
+	return 1;
+}
+
+static u64 get_coherent_dma_mask(struct device *dev)
+{
+	u64 mask = (u64)DMA_BIT_MASK(32);
+
+	if (dev) {
+		mask = dev->coherent_dma_mask;
+
+		/*
+		 * Sanity check the DMA mask - it must be non-zero, and
+		 * must be able to be satisfied by a DMA allocation.
+		 */
+		if (mask == 0) {
+			dev_warn(dev, "coherent DMA mask is unset\n");
+			return 0;
+		}
+
+		if (!__dma_supported(dev, mask, true))
+			return 0;
 	}
 
 	return mask;
@@ -1032,28 +1042,7 @@ void arm_dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
  */
 int dma_supported(struct device *dev, u64 mask)
 {
-	unsigned long limit;
-
-	/*
-	 * If the mask allows for more memory than we can address,
-	 * and we actually have that much memory, then we must
-	 * indicate that DMA to this device is not supported.
-	 */
-	if (sizeof(mask) != sizeof(dma_addr_t) &&
-	    mask > (dma_addr_t)~0 &&
-	    dma_to_pfn(dev, ~0) > arm_dma_pfn_limit)
-		return 0;
-
-	/*
-	 * Translate the device's DMA mask to a PFN limit.  This
-	 * PFN number includes the page which we can DMA to.
-	 */
-	limit = dma_to_pfn(dev, mask);
-
-	if (limit < arm_dma_pfn_limit)
-		return 0;
-
-	return 1;
+	return __dma_supported(dev, mask, false);
 }
 EXPORT_SYMBOL(dma_supported);