Re: [PATCH v5 4/4] PCI: keystone: Add support to build as a loadable module

[Russell King (Oracle)]

On Thu, Nov 13, 2025 at 12:13:55PM -0600, Bjorn Helgaas wrote:
> >  config PCI_KEYSTONE_HOST
> > -	bool "TI Keystone PCIe controller (host mode)"
> > +	tristate "TI Keystone PCIe controller (host mode)"
> >  	depends on ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
> >  	depends on PCI_MSI
> >  	select PCIE_DW_HOST
> > -	select PCI_KEYSTONE
> > +	select PCI_KEYSTONE if ARM
> > +	select PCI_KEYSTONE_TRISTATE if !ARM
> 
> This is kind of a lot of dancing to make keystone built-in on ARM32
> because hook_fault_code() is __init, while making it modular
> everywhere else.
> 
> Is hook_fault_code() __init for some intrinsic reason?  All the
> existing callers are __init, so that's one reason.  But could it be
> made non-__init?

Yes. To discourage use in modules, because there is *no* way to safely
remove a hook.

While one can call hook_fault_code() with a NULL handler, that doesn't
mean that another CPU isn't executing in that function. If that code
gets unmapped while another CPU is executing it (because of a module
being unmapped) then we'll get another fault.

Trying to throw locks at this doesn't help - not without holding locks
over the execution of the called function, which *will* be extremely
detrimental on all fault handling, and probably introduce deadlocks.

-- 
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