Messages in this thread | | | Date | Tue, 3 Jun 2008 15:43:43 +0900 | Subject | Re: [PATCH -mm] x86 calgary: fix handling of devces that aren't behind the Calgary | From | FUJITA Tomonori <> |
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On Tue, 3 Jun 2008 08:21:46 +0300 Muli Ben-Yehuda <muli@il.ibm.com> wrote:
> On Sat, May 31, 2008 at 01:31:33PM +0900, FUJITA Tomonori wrote: > > > The calgary code can give drivers addresses above 4GB which is very > > bad for hardware that is only 32bit DMA addressable: > > > > http://lkml.org/lkml/2008/5/8/423 > > > > This patch tries to fix the problem by using per-device > > dma_mapping_ops support. This fixes the calgary code to use swiotlb > > or nommu properly for devices which are not behind the > > Calgary/CalIOC2. > > > > With this patch, the calgary code sets the global dma_ops to swiotlb > > or nommu, and the dma_ops of devices behind the Calgary/CalIOC2 to > > calgary_dma_ops. So the calgary code can handle devices safely that > > aren't behind the Calgary/CalIOC2. > > This seems a little backward to me. I thought we were going to get rid > of the global dma_ops?
Yeah, I think that we can (though I'm not sure yet if it's the cleanest way to handle IOMMUs). I think that it would better to clean up the x86 IOMMU startup code a bit. Currently, IOMMUs interact too much. It might take time for me to figure out the cleanest way so I tried to fix the Calgary problem in the easiest way.
Yeah, I'm not sure if x86 maintainers are ok with the cleanup. If they are, I'll try.
> If not, assuming going through the global one > would be more efficient, Calgary should be the global one and > nommu/swiotlb should be used on devices that do not have translation > enabled. The reason why is that the majority of devices on a Calgary > system, assuming Calgary is in use, will have translation enabled.
get_dma_ops() checks dev->archdata.dma_ops first then uses the global if device dma_ops is NULL. So I'm not sure about the efficiency.
But I agreed that it's a bit odd to set nommu/swiotlb to the global ops since the majority of devices uses calgary_ops on a Calgary system, as you said. The patch does that just because seems that it's the easiest way to handle devices that aren't behind Calgary.
> In general the patch looks good, barring the point above. We'll give > it a spin on some Calgary/CalIOC2 machines.
Thanks,
Please feel free to drop the patch if you want to fix the problem differently. I just wanted to see how the per-device ops can handle the problem.
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