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SubjectRe: [PATCH 5/8] arm64: irq: add a default handle_irq panic function
On Mon, Feb 22, 2021 at 10:48:11AM +0000, Marc Zyngier wrote:
> On 2021-02-22 09:59, Mark Rutland wrote:
> > On Fri, Feb 19, 2021 at 11:39:01AM +0000, Mark Rutland wrote:
> > > +void (*handle_arch_irq)(struct pt_regs *) __ro_after_init =
> > > default_handle_irq;
> > >
> > > int __init set_handle_irq(void (*handle_irq)(struct pt_regs *))
> > > {
> > > - if (handle_arch_irq)
> > > + if (handle_arch_irq != default_handle_irq)
> > > return -EBUSY;
> > >
> > > handle_arch_irq = handle_irq;
> > > @@ -87,7 +92,7 @@ void __init init_IRQ(void)
> > > init_irq_stacks();
> > > init_irq_scs();
> > > irqchip_init();
> > > - if (!handle_arch_irq)
> > > + if (handle_arch_irq == default_handle_irq)
> > > panic("No interrupt controller found.");
>
> It also seems odd to have both default_handle_irq() that panics,
> and init_IRQ that panics as well. Not a big deal, but maybe
> we should just drop this altogether and get the firework on the
> first interrupt.

My gut feeling was that both were useful, and served slightly different
cases:

* The panic in default_handle_irq() helps if we unexpectedly unmask IRQ
too early. This is mostly a nicety over the current behaviour of
branching to NULL in this case.

* The panic in init_IRQ() gives us a consistent point at which we can
note the absence of a root IRQ controller even if all IRQs are
quiescent. This is a bit nicer to debug than seeing a load of driver
probes fail their request_irq() or whatever.
... so I'd err on the side of keeping both, but if you think otherwise
I'm happy to change this.

Thanks,
Mark.

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