Re: [Xen-devel] [PATCH v2 00/22] Use MSI chip framework to configure MSI/MSI-X in all platforms

[Liviu Dudau <liviu@xxxxxxxxxxx>]

On Fri, Sep 26, 2014 at 11:42:23AM +0800, Yijing Wang wrote:
> >> I am actually in disagreement with you, Thierry. I don't like the general 
> >> direction
> >> of the patches, or at least I don't like the fact that we don't have a 
> >> portable
> >> way of setting up the msi_chip without having to rely on weak 
> >> architectural hooks.
> > 
> > Oh, good. That's actually one of the things I said I wasn't happy with
> > either. =)
> 
> Hm, I decide to drop weak arch_find_msi_chip(), no one likes it.
> Let's find a better solution :)
> 
> > 
> >> I'm surprised no one considers the case of a platform having more than one 
> >> host
> >> bridge and possibly more than one MSI unit. With the current proposed 
> >> patchset I
> >> can't see how that would work.
> > 
> > The PCI core can already deal with that. An MSI chip can be set per bus
> > and the weak pcibios_add_bus() can be used to set that. Often it might
> > not even be necessary to do it via pcibios_add_bus() if you create the
> > root bus directly, since you can attach the MSI chip at that time.
> 
> Yes, PCI hostbridge driver find the matched msi chip during its 
> initialization,
> and assign the msi chip to PCI bus in pcibios_add_bus().
> 
> > 
> >> What I would like to see is a way of creating the pci_host_bridge 
> >> structure outside
> >> the pci_create_root_bus(). That would then allow us to pass this sort of 
> >> platform
> >> details like associated msi_chip into the host bridge and the child busses 
> >> will
> >> have an easy way of finding the information needed by finding the root bus 
> >> and then
> >> the host bridge structure. Then the generic pci_scan_root_bus() can be 
> >> used by (mostly)
> >> everyone and the drivers can remove their kludges that try to work around 
> >> the
> >> current limitations.
> 
> So I think maybe save msi chip in PCI arch sysdata is a good candidate.

Except that arch sysdata at the moment is an opaque pointer. I am all in favour 
in
changing the type of sysdata from void* into pci_host_bridge* and arches can 
wrap their old
sysdata around the pci_host_bridge*.

Best regards,
Liviu

> 
> > 
> > I think both issues are orthogonal. Last time I checked a lot of work
> > was still necessary to unify host bridges enough so that it could be
> > shared across architectures. But perhaps some of that work has
> > happened in the meantime.
> > 
> > But like I said, when you create the root bus, you can easily attach the
> > MSI chip to it.
> > 
> > Thierry
> > 
> 
> 
> -- 
> Thanks!
> Yijing
> 
> 

-- 
-------------------
   .oooO
   (   )
    \ (  Oooo.
     \_) (   )
          ) /
         (_/

 One small step
   for me ...


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