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authorMatthew Wilcox <matthew@wil.cx>2007-10-16 23:31:27 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-17 08:43:06 -0700
commitd1482f40c975e883f209aab659ec75a0afd84075 (patch)
treeb5104116cd40cdd2d06bd1ae555c9558efed6829 /Documentation/DMA-mapping.txt
parent814073620a2eb520c8bb38e0038fd1c78011fe21 (diff)
downloadlwn-d1482f40c975e883f209aab659ec75a0afd84075.tar.gz
lwn-d1482f40c975e883f209aab659ec75a0afd84075.zip
Update DMA-mapping documentation
A couple of updates haven't considered whether the documentation makes sense as a whole any more. Three changes here: - Remove the reference to the "DAC Addressing for Address Space Hungry Devices" section which was deleted by Jan Beulich. - Remove the comment about DMA_24BIT_MASK which became obsolete when Tobias Klauser changed the code to actually use DMA_24BIT_MASK. - Remove the section "64-bit DMA and DAC cycle support" since it's fully covered above, and contains a reference to the section deleted by Jan. Signed-off-by: Matthew Wilcox <willy@linux.intel.com> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/DMA-mapping.txt')
-rw-r--r--Documentation/DMA-mapping.txt20
1 files changed, 0 insertions, 20 deletions
diff --git a/Documentation/DMA-mapping.txt b/Documentation/DMA-mapping.txt
index 3c8ae020b6a7..d84f89dbf921 100644
--- a/Documentation/DMA-mapping.txt
+++ b/Documentation/DMA-mapping.txt
@@ -189,12 +189,6 @@ smaller mask as pci_set_dma_mask(). However for the rare case that a
device driver only uses consistent allocations, one would have to
check the return value from pci_set_consistent_dma_mask().
-If your 64-bit device is going to be an enormous consumer of DMA
-mappings, this can be problematic since the DMA mappings are a
-finite resource on many platforms. Please see the "DAC Addressing
-for Address Space Hungry Devices" section near the end of this
-document for how to handle this case.
-
Finally, if your device can only drive the low 24-bits of
address during PCI bus mastering you might do something like:
@@ -203,8 +197,6 @@ address during PCI bus mastering you might do something like:
"mydev: 24-bit DMA addressing not available.\n");
goto ignore_this_device;
}
-[Better use DMA_24BIT_MASK instead of 0x00ffffff.
-See linux/include/dma-mapping.h for reference.]
When pci_set_dma_mask() is successful, and returns zero, the PCI layer
saves away this mask you have provided. The PCI layer will use this
@@ -652,18 +644,6 @@ It is planned to completely remove virt_to_bus() and bus_to_virt() as
they are entirely deprecated. Some ports already do not provide these
as it is impossible to correctly support them.
- 64-bit DMA and DAC cycle support
-
-Do you understand all of the text above? Great, then you already
-know how to use 64-bit DMA addressing under Linux. Simply make
-the appropriate pci_set_dma_mask() calls based upon your cards
-capabilities, then use the mapping APIs above.
-
-It is that simple.
-
-Well, not for some odd devices. See the next section for information
-about that.
-
Optimizing Unmap State Space Consumption
On many platforms, pci_unmap_{single,page}() is simply a nop.