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Update DMA-mapping documentation

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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>
This commit is contained in:
Matthew Wilcox 2007-10-16 23:31:27 -07:00 committed by Linus Torvalds
parent 814073620a
commit d1482f40c9
1 changed files with 0 additions and 20 deletions
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20
Documentation/DMA-mapping.txt
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@ -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.