dma-mapping: reflow dma_supported

dma_supported has become too much spaghetti for my taste.  Reflow it to
remove the duplicate use_dma_iommu condition and make the main path more
obvious.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Leon Romanovsky <leon@kernel.org>

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 022d670f8cad296bc270eb02c8edb3e895f40f30..b839683da0baf0a8b2c076fe36a5b963a25d988d 100644 (file)
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -841,20 +841,23 @@ static int dma_supported(struct device *dev, u64 mask)
 {
        const struct dma_map_ops *ops = get_dma_ops(dev);
 
-       if (WARN_ON(ops && use_dma_iommu(dev)))
-               return false;
-
-       if (use_dma_iommu(dev))
+       if (use_dma_iommu(dev)) {
+               if (WARN_ON(ops))
+                       return false;
                return true;
+       }
+
        /*
-        * ->dma_supported sets the bypass flag, so we must always call
-        * into the method here unless the device is truly direct mapped.
+        * ->dma_supported sets and clears the bypass flag, so ignore it here
+        * and always call into the method if there is one.
         */
-       if (!ops)
-               return dma_direct_supported(dev, mask);
-       if (!ops->dma_supported)
-               return 1;
-       return ops->dma_supported(dev, mask);
+       if (ops) {
+               if (!ops->dma_supported)
+                       return true;
+               return ops->dma_supported(dev, mask);
+       }
+
+       return dma_direct_supported(dev, mask);
 }
 
 bool dma_pci_p2pdma_supported(struct device *dev)