Re: Aw: Re: [PATCH] pci: mediatek: fix warning in msi.h

[Marc Zyngier]

On 2020-11-02 22:18, Thomas Gleixner wrote:
> On Mon, Nov 02 2020 at 17:16, Thomas Gleixner wrote:
> > On Mon, Nov 02 2020 at 11:30, Marc Zyngier wrote:
> > > --- a/drivers/pci/probe.c
> > > +++ b/drivers/pci/probe.c
> > > @@ -871,6 +871,8 @@ static void pci_set_bus_msi_domain(struct pci_bus
> > > *bus)
> > >   		d = pci_host_bridge_msi_domain(b);
> > >
> > >   	dev_set_msi_domain(&bus->dev, d);
> > > +	if (!d)
> > > +		bus->bus_flags |= PCI_BUS_FLAGS_NO_MSI;
> >
> > Hrm, that might break legacy setups (no irqdomain support). I'd rather
> > prefer to explicitly tell the pci core at host registration time.
>
> s/might break/ breaks /     Just validated :)

For my own edification, can you point me to the failing case?

> So we really need some other solution and removing the warning is not 
> an
> option. If MSI is enabled then we want to get a warning when a PCI
> device has no MSI domain associated. Explicitly expressing the PCIE
> brigde misfeature of not supporting MSI is way better than silently
> returning an error code which is swallowed anyway.

I don't disagree here, though the PCI_MSI_ARCH_FALLBACKS mechanism
makes it more difficult to establish.

> Whatever the preferred way is via flags at host probe time or flagging
> it post probe I don't care much as long as it is consistent.

Host probe time is going to require some changes in the core PCI api,
as everything that checks for a MSI domain is based on the pci_bus
structure, which is only allocated much later.

I'll have a think.

        M.
--
Jazz is not dead. It just smells funny...