linux-kernel - Re: [PATCH v2] [ARM] gic: Unmask private interrupts on all cores during IRQ enable

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Message-ID: <20101216150357.GT9937@n2100.arm.linux.org.uk>
Date:	Thu, 16 Dec 2010 15:03:57 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Stephen Caudle <scaudle@...eaurora.org>
Cc:	dwalker@...eaurora.org, linux-arm-msm@...r.kernel.org,
	adharmap@...eaurora.org, linux-kernel@...r.kernel.org,
	miltonm@....com, linux-arm-kernel@...ts.infradead.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] [ARM] gic: Unmask private interrupts on all cores
	during IRQ enable

On Thu, Dec 16, 2010 at 09:54:23AM -0500, Stephen Caudle wrote:
> On 12/09/2010 11:24 AM, Stephen Caudle wrote:
> >> It is also unreasonable to have one core enabling the PPI on other
> >> cores where the hardware behind the interrupt may not have been
> >> initialized yet.  If it is a private interrupt for a private peripheral,
> >> then only the associated CPU should be enabling that interrupt.
> >>
> >> I guess this is something which genirq can't cope with, in which case
> >> either genirq needs to be modified to cope with private CPU interrupts,
> >> which are controlled individually by their associated CPU, or we need a
> >> private interface to support this.
> > 
> > I see your point.  Our immediate need for this is to support a
> > performance monitor interrupt that happens to be a PPI.  It is used by
> > perf events (and subsequently, oprofile).
> > 
> > Since PPIs are so machine-specific, I started looking into patching
> > perf_events.c by adding a machine specific function to handle the PMU
> > IRQ request.  For mach-msm, we would call request_irq like normal, but
> > also unmask the performance monitor interrupt on the other cores.  The
> > downside to this is that a machine specific implementation would be
> > needed anytime a PPI is requested, not just in perf_events.c.
> > 
> > Then, I saw Thomas' email regarding our local timer PPI:
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2010-December/033840.html.
> > 
> > Russell, before I submit another patch, I would like to know if you
> > prefer a more generic approach like Thomas suggests, or a
> > machine-specific approach like I have described?
> 
> Russell, what are your thoughts on this?

I've not changed my thoughts on this.  PPIs should not be handled by
genirq - it just doesn't make sense for them to be.
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