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

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Date:   Wed, 12 Jul 2023 19:25:24 +0300
From:   Sergey Shtylyov <s.shtylyov@....ru>
To:     Guenter Roeck <linux@...ck-us.net>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        David Laight <David.Laight@...LAB.COM>,
        'John Paul Adrian Glaubitz' <glaubitz@...sik.fu-berlin.de>,
        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 7:22 PM, Sergey Shtylyov 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.

   x86 too. PowerPC used to do that too, IIRC...

>> They are NOT the platform drivers we're dealing with here...

>> Guenter

MBR, Sergey