Re: [PATCH 1/6] powerpc/kconfig: Move NR_IRQS into "Kernel Options"

[Arnd Bergmann <arnd@arndb.de>]

On Monday 12 October 2015 21:00:25 Michael Ellerman wrote:
> On Thu, 2015-10-08 at 23:30 +0200, Arnd Bergmann wrote:
> > On Friday 09 October 2015 08:09:12 Michael Ellerman wrote:
> > > Currently the NR_IRQS option sits at the top level, which is ugly in
> > > menuconfig. It's not something users will commonly need to worry about
> > > so move it into "Kernel Options".
> > 
> > Is this option actually still meaningful at all, when you select CONFIG_SPARSE_IRQ
> > unconditionally?
> 
> It's still used for #define NR_IRQS, which is still used by the generic irq
> code and also some drivers.

Drivers shouldn't use it, and I don't see any driver using it that can be
enabled on powerpc.

The question is rather whether you have any devices on powerpc that
get a hardwired IRQ number from a statically defined platform device
rather from DT.

If there are any ISA devices, the driver might try to use an interrupt
number that is hardcoded in the driver as a number from 0 to 15.
I guess that could happen on old CHRP or 6xx machines.

> So we need some value for that, whether it needs to be user defined or if we
> could just pick a value I'm not sure. x86 seem to just define it based on
> NR_CPUs and some other factors.

What happens if you set it to 16?

	Arnd