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-rw-r--r--Documentation/usb/dma.txt11
1 files changed, 6 insertions, 5 deletions
diff --git a/Documentation/usb/dma.txt b/Documentation/usb/dma.txt
index e8b50b7de9d9..cfdcd16e3abf 100644
--- a/Documentation/usb/dma.txt
+++ b/Documentation/usb/dma.txt
@@ -6,8 +6,9 @@ in the kernel usb programming guide (kerneldoc, from the source code).
6API OVERVIEW 6API OVERVIEW
7 7
8The big picture is that USB drivers can continue to ignore most DMA issues, 8The big picture is that USB drivers can continue to ignore most DMA issues,
9though they still must provide DMA-ready buffers (see DMA-mapping.txt). 9though they still must provide DMA-ready buffers (see
10That's how they've worked through the 2.4 (and earlier) kernels. 10Documentation/PCI/PCI-DMA-mapping.txt). That's how they've worked through
11the 2.4 (and earlier) kernels.
11 12
12OR: they can now be DMA-aware. 13OR: they can now be DMA-aware.
13 14
@@ -62,8 +63,8 @@ and effects like cache-trashing can impose subtle penalties.
62 force a consistent memory access ordering by using memory barriers. It's 63 force a consistent memory access ordering by using memory barriers. It's
63 not using a streaming DMA mapping, so it's good for small transfers on 64 not using a streaming DMA mapping, so it's good for small transfers on
64 systems where the I/O would otherwise thrash an IOMMU mapping. (See 65 systems where the I/O would otherwise thrash an IOMMU mapping. (See
65 Documentation/DMA-mapping.txt for definitions of "coherent" and "streaming" 66 Documentation/PCI/PCI-DMA-mapping.txt for definitions of "coherent" and
66 DMA mappings.) 67 "streaming" DMA mappings.)
67 68
68 Asking for 1/Nth of a page (as well as asking for N pages) is reasonably 69 Asking for 1/Nth of a page (as well as asking for N pages) is reasonably
69 space-efficient. 70 space-efficient.
@@ -93,7 +94,7 @@ WORKING WITH EXISTING BUFFERS
93Existing buffers aren't usable for DMA without first being mapped into the 94Existing buffers aren't usable for DMA without first being mapped into the
94DMA address space of the device. However, most buffers passed to your 95DMA address space of the device. However, most buffers passed to your
95driver can safely be used with such DMA mapping. (See the first section 96driver can safely be used with such DMA mapping. (See the first section
96of DMA-mapping.txt, titled "What memory is DMA-able?") 97of Documentation/PCI/PCI-DMA-mapping.txt, titled "What memory is DMA-able?")
97 98
98- When you're using scatterlists, you can map everything at once. On some 99- When you're using scatterlists, you can map everything at once. On some
99 systems, this kicks in an IOMMU and turns the scatterlists into single 100 systems, this kicks in an IOMMU and turns the scatterlists into single