linux-kernel - Re: [PATCH] genirq: do not mask interrupts by default

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Message-Id: <1174982665.14065.5.camel@localhost.localdomain>
Date:	Tue, 27 Mar 2007 18:04:24 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...l.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Mackerras <paulus@...ba.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [PATCH] genirq: do not mask interrupts by default

On Tue, 2007-03-27 at 09:32 +0200, Ingo Molnar wrote:
> * Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> 
> > Note that I'm not opposed to the change at all, I think it's a good 
> > idea, I'm just worried I'm discovering it a bit late and I've seen 
> > PICs broken in some many colorful ways that I'm a bit worried... Oh 
> > well...
> 
> This change does not really change irq-flow semantics, what it does is 
> that disable_irq()'s effect is delayed. The irq controller does not have 
> to re-assert the irq, we've got the soft-resend mechanism. What am i 
> missing? Are you worried about this change causing actual breakage? (and 
> i'm sorry about not having Cc:-ed you explicitly, i could have sworn you 
> were included in that discussion but apparently not!)

I'm worried about some broken controllers I know of that might indeed
swallow the interrupt if it occurs, we ack it, then disable it, and
later on re-enable it...

I think the main case I have in mind (pmac-pic) has the necessary
retrigger all over the place but there is definitely a change in the
flow of disabling/enabling here.

Anyway, I'll run some tests tomorrow and make noise if I find something
broken, though I can't test the various embedded thingies in
arch/powerpc.

Ben.


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