dma-mapping: deprecate dma_zalloc_coherent

We now always return zeroed memory from dma_alloc_coherent.  Note that
simply passing GFP_ZERO to dma_alloc_coherent wasn't always doing the
right thing to start with given that various allocators are not backed
by the page allocator and thus would ignore GFP_ZERO.
Signed-off-by: NChristoph Hellwig <hch@lst.de>

Documentation/DMA-API.txt

@@ -58,15 +58,6 @@ specify the ``GFP_`` flags (see kmalloc()) for the allocation (the
 implementation may choose to ignore flags that affect the location of
 the returned memory, like GFP_DMA).
 
-::
-
-	void *
-	dma_zalloc_coherent(struct device *dev, size_t size,
-			    dma_addr_t *dma_handle, gfp_t flag)
-
-Wraps dma_alloc_coherent() and also zeroes the returned memory if the
-allocation attempt succeeded.
-
 ::
 
 	void

include/linux/dma-mapping.h

@@ -644,12 +644,13 @@ static inline unsigned long dma_max_pfn(struct device *dev)
 }
 #endif
 
+/*
+ * Please always use dma_alloc_coherent instead as it already zeroes the memory!
+ */
 static inline void *dma_zalloc_coherent(struct device *dev, size_t size,
 					dma_addr_t *dma_handle, gfp_t flag)
 {
-	void *ret = dma_alloc_coherent(dev, size, dma_handle,
-				       flag | __GFP_ZERO);
-	return ret;
+	return dma_alloc_coherent(dev, size, dma_handle, flag);
 }
 
 static inline int dma_get_cache_alignment(void)