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SubjectRe: PATCH 2.4.0 parisc PCI support

Ivan Kokshaysky wrote:
> Well, it seems that I finally see what is wrong with your code, and
> why it worked in your case. You assume that "window" resources of
> the bridge are already known when we call pbus_assign_resources_sorted().
> This is incorrect. we know the "sizes" of all child resources from the bus walk?
I'll check that and see if it can be safely changed.

> Probably you rely on pci_read_bridge_bases() doing
> something meaningful (I looked at the parisc pci code in current 2.4.x,
> don't know about your CVS tree).

Nope - don't call that for A500 (machines with PDC PAT)...that might in
fact be another problem later related to some PDC (aka BIOS) changes.

> Yes, at least some of the DEC bridges
> after power-up/reset have 0s in base/limit registers. This means
> that you have ranges 0000-0fff (4K) for IO and 00000000-000fffff (1M)
> for MEM. Obviously it's enough to hold all resources on the
> cards you've tested, but it won't work in common case. There is
> a lot of reasons why; just a couple of them:
> - according to PPB specification, base/limits registers of the bridge
> after reset are *undefined*, so you'll probably have troubles
> with non-DEC bridges.
> - there is a number of alpha systems with a built-in PCI-PCI bridge
> and real PCI slots behind it. Obviously 4K/1M isn't enough for
> these systems, and it was the main reason of rewriting that code.
> etc etc etc.

Yup - I think you are right on all counts here.
I'll rework the parisc code tonight/tomorrow and see if I can get rid
of the contentious generic PCI changes. I should be able to.

> Basically, you won't know bridge "window" size for a given bus until
> you'll have allocated *all* devices on *all* its child busses.

Linux doesn't. It's possible to deal with window register size in
the initial bus walk (where BAR sizes are determined).

> Besides, including bridge resources in the "sort lists" is meaningless,
> since these resources have fixed alignment - 4K for IO and 1M for MEM,
> unlike "regular" ones, which alignment == size.

The alignment would have to be handled correctly and I thought
pcibios_align_resource() did that. I see now the arch/parisc one doesn't
and others probably don't either. Let me think about this more...

> Unfortunately I haven't anything with a bridge handy at the moment
> to test that patch. Besides, we'll have here a sort of holidays till
> Sunday. So maybe next week...

np. thanks.

> > I don't think existing PCI code is very "dirty".
> I hope so. :-)


> However, some problems need to be worked out:
> 1. generic vs. arch code - we've already discussed some of these
> 2. Prefetchable Memory - do we need to deal with it? Though looking
> at modern x86 systems I tend to keep it disabled :-)

Ditto for parisc.

> 3. pdev_enable_device() - it's a bit ugly, confuses people and
> possibly is not needed at all.



Grant Grundler
parisc-linux {PCI|IOMMU|SMP} hacker
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