Re: [patch RFC 30/38] PCI/MSI: Allow to disable arch fallbacks

[Thomas Gleixner]

On Tue, Aug 25 2020 at 15:07, Bjorn Helgaas wrote:
>> + * The arch hooks to setup up msi irqs. Default functions are implemented
>> + * as weak symbols so that they /can/ be overriden by architecture specific
>> + * code if needed.
>> + *
>> + * They can be replaced by stubs with warnings via
>> + * CONFIG_PCI_MSI_DISABLE_ARCH_FALLBACKS when the architecture fully
>> + * utilizes direct irqdomain based setup.
>
> Do you expect *all* arches to eventually use direct irqdomain setup?

Ideally that happens some day. We have five left when x86 is converted:

IA64, MIPS, POWERPC, S390, SPARC

IA64 is unlikely to be fixed, but might be solved naturally by removal.

For the others I don't know, but it's not on the horizon anytime soon I
fear.

> And in that case, to remove the config option?

Yes, and all the code which depends on it.

> If not, it seems like it'd be nicer to have the burden on the arches
> that need/want to use arch-specific code instead of on the arches that
> do things generically.

Right, but they still share the common code there and some of them
provide only parts of the weak callbacks. I'm not sure whether it's a
good idea to copy all of this into each affected architecture.

Or did you just mean that those architectures should select
CONFIG_I_WANT_THE CRUFT instead of opting out on the fully irq domain
based ones?

Thanks,

        tglx