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

On 7/12/23 6:38 PM, Guenter Roeck 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.

   It seems you still don't understand... The i8253 drivers using IRQ0 live in
the arch/{mips|x86}/kernel/ code, so they're allowed to claim IRQ0 via calling
request_irq() (MIPS still does it.  They are NOT the platform drivers we're
dealing with here...

> Guenter

MBR, Sergey