linux-kernel - Re: [PATCH] x86: Fix XT-PIC-XT-PIC in /proc/interrupts

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Message-ID: <20141027124409.GA22947@gmail.com>
Date:	Mon, 27 Oct 2014 13:44:09 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Fix XT-PIC-XT-PIC in /proc/interrupts


* Maciej W. Rozycki <macro@...ux-mips.org> wrote:

> On Mon, 27 Oct 2014, Ingo Molnar wrote:
> 
> > What's the effect of this change on the output for non-8259A irq 
> > controllers?
> 
>  Good question, I didn't expect any other IRQ controller to be used for 
> ISA interrupts (the APIC is handled elsewhere).  I have checked the 
> sources and the only other controller that can be used for `legacy_pic' 
> is `dummy_irq_chip' (cf. `default_legacy_pic' vs `null_legacy_pic' in 
> arch/x86/kernel/i8259.c).  That affects `init_ISA_irqs' only (the other 
> place, `make_8259A_irq', has a reference to `i8259A_chip' hardcoded).
> 
>  In this case the output would change from "dummy-dummy" to "dummy", 
> which IMHO has just as much value as the change from "XT-PIC-XT-PIC" to 
> "XT-PIC".  However I don't think you'd be able to request such IRQs so 
> they will never show up in /proc/interrupts, making this observation 
> largely irrelevant.  If you think I may be wrong here, then can you 
> please find such a system and try this change with it (or can someone 
> else reading this make this check for me by any chance)?  Unfortunately 
> all x86 hardware I have does have an 8259A pair.
> 
>  Also please note that both places explicitly refer to the name of the 
> IRQ chip being installed as the name of the handler as well, with 
> `i8259A_chip.name' and `chip->name' respectively, this is hardcoded.  
> So no matter which chip is used there'll be a duplicate name in 
> /proc/interrupts.
> 
>  Does this answer address your concern?

Yeah, it addresses it, I'll queue up your fix, thanks!

	Ingo
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