Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc

[sfrench/cifs-2.6.git] / Documentation / DMA-API-HOWTO.txt

diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
index 979228bc9035ca35463a6adfb9db2a7c9f40f9a1..4ed388356898435a12670581083a9036a71131bb 100644 (file)
--- a/Documentation/DMA-API-HOWTO.txt
+++ b/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.