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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>
This commit is contained in:
Christoph Hellwig 2017-05-22 10:58:49 +02:00
parent 9eef8b8cc2
commit f51f288e23
2 changed files with 5 additions and 31 deletions
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31
Documentation/DMA-API-HOWTO.txt
View File

@ -550,32 +550,11 @@ and to unmap it:
dma_unmap_single(dev, dma_handle, size, direction); dma_unmap_single(dev, dma_handle, size, direction);
You should call dma_mapping_error() as dma_map_single() could fail and return 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. error. Doing so will ensure that the mapping code will work correctly on all
However, it is a good practice to call dma_mapping_error() interface, which DMA implementations without any dependency on the specifics of the underlying
will invoke the generic mapping error check interface. Doing so will ensure implementation. Using the returned address without checking for errors could
that the mapping code will work correctly on all DMA implementations without result in failures ranging from panics to silent data corruption. The same
any dependency on the specifics of the underlying implementation. Using the applies to dma_map_page() as well.
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;
}
You should call dma_unmap_single() when the DMA activity is finished, e.g., 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. from the interrupt which told you that the DMA transfer is done.

5
include/linux/dma-mapping.h
View File

@ -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) if (get_dma_ops(dev)->mapping_error)
return get_dma_ops(dev)->mapping_error(dev, dma_addr); return get_dma_ops(dev)->mapping_error(dev, dma_addr);
#ifdef DMA_ERROR_CODE
return dma_addr == DMA_ERROR_CODE;
#else
return 0; return 0;
#endif
} }
#ifndef HAVE_ARCH_DMA_SUPPORTED #ifndef HAVE_ARCH_DMA_SUPPORTED