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

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Message-ID: <b02489c7-96de-b6ed-07b9-9ba423af34c6@roeck-us.net>
Date:   Wed, 12 Jul 2023 08:38:38 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Sergei Shtylyov <sergei.shtylyov@...il.com>,
        David Laight <David.Laight@...LAB.COM>,
        'John Paul Adrian Glaubitz' <glaubitz@...sik.fu-berlin.de>,
        Sergey Shtylyov <s.shtylyov@....ru>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sh: Avoid using IRQ0 on SH3 and SH4

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