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

[Thierry Reding <thierry.reding@xxxxxxxxx>]

On Thu, Sep 25, 2014 at 03:48:55PM +0100, Liviu Dudau wrote:
> On Thu, Sep 25, 2014 at 09:42:36AM +0200, Thierry Reding wrote:
> > On Thu, Sep 25, 2014 at 11:14:10AM +0800, Yijing Wang wrote:
> > > This series is based Bjorn's pci/msi branch
> > > git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git pci/msi
> > > 
> > > Currently, there are a lot of weak arch functions in MSI code.
> > > Thierry Reding Introduced MSI chip framework to configure MSI/MSI-X in 
> > > arm.
> > > This series use MSI chip framework to refactor MSI code across all 
> > > platforms
> > > to eliminate weak arch functions. Then all MSI irqs will be managed in a 
> > > unified framework. Because this series changed a lot of ARCH MSI code,
> > > so tests in the platforms which MSI code modified are warmly welcomed!
> > 
> > Apart from the comments to the individual patches I very much like where
> > this is going. Thanks for taking care of this.
> > 
> > Thierry
> 
> 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. =)

> 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.

> 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.

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

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