dma-mapping: remove DMA_ERROR_CODE

And update the documentation - dma_mapping_error has been supported
everywhere for a long time.
Signed-off-by: Christoph Hellwig <hch@lst.de>

Documentation/DMA-API-HOWTO.txt

@@ -550,32 +550,11 @@ and to unmap it:
 	dma_unmap_single(dev, dma_handle, size, direction);
 
 You should call dma_mapping_error() as dma_map_single() could fail and return
-error. Not all DMA implementations support the dma_mapping_error() interface.
-However, it is a good practice to call dma_mapping_error() interface, which
-will invoke the generic mapping error check interface. Doing so will ensure
-that the mapping code will work correctly on all DMA implementations without
-any dependency on the specifics of the underlying implementation. Using the
-returned address without checking for errors could result in failures ranging
-from panics to silent data corruption. A couple of examples of incorrect ways
-to check for errors that make assumptions about the underlying DMA
-implementation are as follows and these are applicable to dma_map_page() as
-well.
-
-Incorrect example 1:
-	dma_addr_t dma_handle;
-
-	dma_handle = dma_map_single(dev, addr, size, direction);
-	if ((dma_handle & 0xffff != 0) || (dma_handle >= 0x1000000)) {
-		goto map_error;
-	}
-
-Incorrect example 2:
-	dma_addr_t dma_handle;
-
-	dma_handle = dma_map_single(dev, addr, size, direction);
-	if (dma_handle == DMA_ERROR_CODE) {
-		goto map_error;
-	}
+error.  Doing so will ensure that the mapping code will work correctly on all
+DMA implementations without any dependency on the specifics of the underlying
+implementation. Using the returned address without checking for errors could
+result in failures ranging from panics to silent data corruption.  The same
+applies to dma_map_page() as well.
 
 You should call dma_unmap_single() when the DMA activity is finished, e.g.,
 from the interrupt which told you that the DMA transfer is done.

include/linux/dma-mapping.h

@@ -546,12 +546,7 @@ static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
 
 	if (get_dma_ops(dev)->mapping_error)
 		return get_dma_ops(dev)->mapping_error(dev, dma_addr);
-
-#ifdef DMA_ERROR_CODE
-	return dma_addr == DMA_ERROR_CODE;
-#else
 	return 0;
-#endif
 }
 
 #ifndef HAVE_ARCH_DMA_SUPPORTED