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Diffstat (limited to 'Documentation/DMA-API-HOWTO.txt')
| -rw-r--r-- | Documentation/DMA-API-HOWTO.txt | 15 |
1 files changed, 7 insertions, 8 deletions
diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt index 1a721d0f35c8..cb712a02f59f 100644 --- a/Documentation/DMA-API-HOWTO.txt +++ b/Documentation/DMA-API-HOWTO.txt @@ -147,7 +147,7 @@ networking subsystems make sure that the buffers they use are valid for you to DMA from/to. DMA addressing capabilities -========================== +=========================== By default, the kernel assumes that your device can address 32-bits of DMA addressing. For a 64-bit capable device, this needs to be increased, and for @@ -365,13 +365,12 @@ __get_free_pages() (but takes size instead of a page order). If your driver needs regions sized smaller than a page, you may prefer using the dma_pool interface, described below. -The consistent DMA mapping interfaces, for non-NULL dev, will by -default return a DMA address which is 32-bit addressable. Even if the -device indicates (via DMA mask) that it may address the upper 32-bits, -consistent allocation will only return > 32-bit addresses for DMA if -the consistent DMA mask has been explicitly changed via -dma_set_coherent_mask(). This is true of the dma_pool interface as -well. +The consistent DMA mapping interfaces, will by default return a DMA address +which is 32-bit addressable. Even if the device indicates (via the DMA mask) +that it may address the upper 32-bits, consistent allocation will only +return > 32-bit addresses for DMA if the consistent DMA mask has been +explicitly changed via dma_set_coherent_mask(). This is true of the +dma_pool interface as well. dma_alloc_coherent() returns two values: the virtual address which you can use to access it from the CPU and dma_handle which you pass to the |