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Subject: Re: [PATCH] sh: Avoid using IRQ0 on SH3 and SH4
To:     Guenter Roeck <linux@roeck-us.net>,
        Sergei Shtylyov <sergei.shtylyov@gmail.com>,
        David Laight <David.Laight@ACULAB.COM>,
        'John Paul Adrian Glaubitz' <glaubitz@physik.fu-berlin.de>,
        Geert Uytterhoeven <geert@linux-m68k.org>
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        Rich Felker <dalias@libc.org>,
        "linux-sh@vger.kernel.org" <linux-sh@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Sergey Shtylyov <s.shtylyov@omp.ru>
Organization: Open Mobile Platform
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Date:   Wed, 12 Jul 2023 19:22:54 +0300
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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