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

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Date:   Wed, 12 Jul 2023 10:15:43 +0200
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     David Laight <David.Laight@...LAB.COM>,
        Guenter Roeck <linux@...ck-us.net>,
        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

Hi David!

On Wed, 2023-07-12 at 08:12 +0000, David Laight wrote:
> From: John Paul Adrian Glaubitz
> > 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+ ?

That would make things more complicated as IRQ0 would have to be
handled individually.

> At least that would only cause issues for code that needed
> to use IRQ_0.

What issues are you seeing or expecting?

> (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.)

It's invalid for driver code, not for architecture code.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
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