On Thu, Oct 13, 2016 at 02:40:35PM +0800, Peter Xu wrote:
> > > > + return pci_translate_addr(dev, addr);
> > >
> > > Raw question: do we need to translate bar addresses as well?
> >
> > I believe, yes.
> >
> > Unless we always have identity mapping between PCI address space and
> > CPU physical address space I can not realize how could it be done
> > otherwise. But even if we were, I would leave the translation routine
> > for clarity.
>
> Sorry I didn't quite catch your point. Are we talking about IOMMU
> address remapping here? IMHO BAR addresses are from CPU's point of
> view. It's only used by CPU, not device. In that case, BAR address
> should not be translated at least by IOMMU (no matter for x86/arm or
> whatever).
>
> Take Linux as example: pci_ioremap_bar() is responsible to be called
> for any PCI drivers to map device memory bars into kernel virtual
> address space. Basically it does:
>
> void __iomem *pci_ioremap_bar(struct pci_dev *pdev, int bar)
> {
> struct resource *res = &pdev->resource[bar];
> return ioremap_nocache(res->start, resource_size(res));
> }
>
> So as it is written: I believe we don't translate the bar address
> (which should be res->start). We use it as physical address.
>
> Or, do you mean other kinds of translation that I don't aware of?
Yes, I mean translation from PCI bus address space to CPU physical
address space. These two busses are different and hence need a
translation. I assume Linux pci_dev::resource[] have translated
address, but it is not what PCI devices see. Unless I do not terribly
missing somethig, BAR addresses is what a device sees on its AD[0..31]
pins.
> Another silly question: I see pci_translate_addr() defined in both
> lib/x86/asm/pci.h and lib/asm-generic/pci-host-bridge.h. How's that
> working?
So an architecutre should implement pci_translate_addr() in order
to provide mapping between PCI bus address and CPU physical address.
These two are the implementations.
Thanks!
> Thanks,
>
> -- peterx
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