Re: [PATCH] sh: Avoid using IRQ0 on SH3 and SH4

[Guenter Roeck]

On 7/12/23 01:20, Sergei Shtylyov wrote:
> On 7/12/23 11:12 AM, David Laight wrote:
>
> > > Sent: 09 July 2023 00:13
> > ....
> > > Looking at arch/sh/boards/mach-r2d/irq.c, there is some IRQ translation going
> > > on and maybe that's the part where we need to correct the offset by 16?
> >
> > Would it be less problematic to use (say) 16 for IRQ_0
> > leaving IRQ_1+ as 1+ ?
>
>     I don't think so.
>
> > At least that would only cause issues for code that needed
> > to use IRQ_0.
> >
> > (It has to be said that making IRQ 0 invalid seemed wrong
> > to me. x86 (IBM PC) gets away with it because IRQ 0 is
> > always assigned to platform specific hardware.)
>
>     Not only x86, IIRC.
>     Have you seen the commit below?
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ce753ad1549cbe9ccaea4c06a1f5fa47432c8289

Quoting:

using IRQ0 is considered invalid (according to Linus) outside the arch/ code
                                                      ^^^^^^^^^^^^^^^^^^^^^^

The changes here were made _in_ the arch code. While there may be valid
arguments for doing that, quoting the above commit as reason isn't really
sufficient.

Guenter