Re: [PATCH v4 05/19] irqchip: add nps Internal and external irqchips

From: Marc Zyngier
Date: Tue Jan 12 2016 - 04:28:26 EST

On 12/01/16 09:12, Vineet Gupta wrote:


>> HANDLE_DOMAIN_IRQ is not mandatory at all - a number of architectures
>> had something open-coded in the past (with some drawbacks and/or bugs),
>> and this config option is just one of the ways to get it right.
>> MIPS/PPC perform the reverse lookup directly, without using this
>> infrastructure, and that would be a valid approach for ARC too.
> I'd rather use the generic infrastructure and improve it if needed !
>>>> Marc, I hope you are back from holidays. When u get a chance could you please
>>>> respond to above.
>>>> Also I tool a stab at it anyways.
>>>> 1. Enabled HANDLE_DOMAIN_IRQ
>>>> 2. arch_do_IRQ() calls handle_domain_irq(NULL, hwirq, regs) since that code
>>>> doesn't know about domains.
>>>> It fails w/o irq_set_default_host() being called.
>> Well, that's expected. unless you use the underlying primitive
>> (__handle_domain_irq) and pass false as the parameter for lookup (see
>> handle_IRQ() in arch/arm/kernel/irq.c). This is what we use for "legacy"
>> platforms that do not support domains.
> Right I saw that and that causes virq = hwirq - kind of defeats the purpose if we
> were doing this on ARC.

You can forget about this if you convert all your platforms to using
domains. But if you have to deal with a transition period (which, in the
ARM case, will last exactly forever because some platforms will never be
converted to DT), this comes in handy.

>>>> If we go back to sunxi example you quoted above, it relies on driver passing the
>>>> domain to handle_domain_irq(). IMHO it is simpler if we had the default domain.
>>>> So long story short, ARC can be made to use handle_domain_irq() w/o the song and
>>>> dance of registering another callback from irqchip code if we retained the default
>>>> domain setting.
>> This only works if you can guarantee that you will never have another
>> irqchip calling irq_set_default_host()... If your system is always
>> simple enough to guarantee that, why not.
> ATM we can certainly assume that.
> However with ARM approach two irqchips can still call set_handle_irq() and only
> the first one succeeds (and others return silently). That seems wrong to me -
> irq_xxx.c will still use the handler registered by say irq_sun41.c ?

Oh, this is by no mean foolproof. We do rely on irqchips installing
their primary handler only if they are truly the primary irqchip (they
do not have a parent). Anything else will fail badly.

So if you're confident that you can ensure that noone will set de
default domain twice, you'll be fine.


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