powerpc: Swiotlb breaks pseries

Turning on SWIOTLB selects or enables PPC_NEED_DMA_SYNC_OPS, which means
we get the non empty versions of dma_sync_* in asm/dma-mapping.h

On my pseries machine the dma_ops have no such routines and we die with
a null pointer - this patch gets it booting, is there a more elegant way
to do it?
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

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

@@ -309,7 +309,9 @@ static inline void dma_sync_single_for_cpu(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
-	dma_ops->sync_single_range_for_cpu(dev, dma_handle, 0,
+
+	if (dma_ops->sync_single_range_for_cpu)
+		dma_ops->sync_single_range_for_cpu(dev, dma_handle, 0,
 					   size, direction);
 }
 
@@ -320,7 +322,9 @@ static inline void dma_sync_single_for_device(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
-	dma_ops->sync_single_range_for_device(dev, dma_handle,
+
+	if (dma_ops->sync_single_range_for_device)
+		dma_ops->sync_single_range_for_device(dev, dma_handle,
 					      0, size, direction);
 }
 
@@ -331,7 +335,9 @@ static inline void dma_sync_sg_for_cpu(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
-	dma_ops->sync_sg_for_cpu(dev, sgl, nents, direction);
+
+	if (dma_ops->sync_sg_for_cpu)
+		dma_ops->sync_sg_for_cpu(dev, sgl, nents, direction);
 }
 
 static inline void dma_sync_sg_for_device(struct device *dev,
@@ -341,7 +347,9 @@ static inline void dma_sync_sg_for_device(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
-	dma_ops->sync_sg_for_device(dev, sgl, nents, direction);
+
+	if (dma_ops->sync_sg_for_device)
+		dma_ops->sync_sg_for_device(dev, sgl, nents, direction);
 }
 
 static inline void dma_sync_single_range_for_cpu(struct device *dev,
@@ -351,7 +359,9 @@ static inline void dma_sync_single_range_for_cpu(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
-	dma_ops->sync_single_range_for_cpu(dev, dma_handle,
+
+	if (dma_ops->sync_single_range_for_cpu)
+		dma_ops->sync_single_range_for_cpu(dev, dma_handle,
 					   offset, size, direction);
 }
 
@@ -362,7 +372,9 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
-	dma_ops->sync_single_range_for_device(dev, dma_handle, offset,
+
+	if (dma_ops->sync_single_range_for_device)
+		dma_ops->sync_single_range_for_device(dev, dma_handle, offset,
 					      size, direction);
 }
 #else /* CONFIG_PPC_NEED_DMA_SYNC_OPS */