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SubjectRe: [PATCH 5/8] arm64: irq: add a default handle_irq panic function
On 2021-02-22 11:25, Mark Rutland wrote:
> 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.

As I said, it's not a big deal. I doubt that we'll see
default_handle_irq()
exploding in practice. But the real nit here is the difference of
treatment
between IRQ and FIQ. *IF* we ever get a system that only signals its
interrupt as FIQ (and I don't see why we'd forbid that), then we would

To be clear, I don't think we should care too much either way, and I'm
fine with the code as is.

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

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