Messages in this thread | | | Subject | Re: [PATCH] RFC: kills consistent_dma_mask | From | Jes Sorensen <> | Date | 19 Aug 2003 05:21:08 -0400 |
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>>>>> "Krzysztof" == Krzysztof Halasa <khc@pm.waw.pl> writes:
Krzysztof> "David S. Miller" <davem@redhat.com> writes: >> The ia64 support code to do things with consistent_dma_mask just >> isn't in the tree yet.
Krzysztof> Ok. Any pointer so I can see how is it used?
drivers/net/tg3.c was the case where we needed it first. If you grab the official ia64 kernel patch and look in the arch/ia64/sn/io code you will find places that consider it.
>> Because the other platforms don't to do anything special wrt. this >> they can just ignore consitent_dma_mask altogether.
Krzysztof> No. The documentation states that consistent_dma_mask (and Krzysztof> not dma_mask) will be used when doing Krzysztof> pci_alloc_consistent(). This is, obviously, false on most Krzysztof> platforms.
It's not being used on those platforms because I couldn't implement it on all of them - I just don't have the hardware. We implemented it on ia64 because thats where we needed it, Andi Kleen then implemented it on x86_64 because he needed it there. If there are PPC boxes out there with similar issues then I am sure that the PPC maintainers will implement support for this when they need it.
Krzysztof> It is perfectly reasonable to expect that Krzysztof> setting consistent_dma_mask to, say, 28 bits will cause Krzysztof> pci_alloc_consistent to return memory from first 256 Krzysztof> MB. This is not true on most platforms, for example i386 Krzysztof> happily allocs memory near the top in such case.
The default for pci_alloc_consistent() on ia32 is that pci_dev->consistent_dma_mask == 32 bit. If you need something else for a reason, please feel free to implement support for it.
Krzysztof> If we really need two masks, they can't be ignored on some Krzysztof> archs.
So *fix* it! This is Linux, it's Free Software, you have the source, you have the right to fix bugs!
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