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

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Date:	Mon, 27 Oct 2014 12:29:44 +0000 (GMT)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Ingo Molnar <mingo@...nel.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

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?

  Maciej
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