linux-kernel - Re: [PATCH] AMD Thermal Interrupt Support

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Message-ID: <3f1a065b0712271057s150b62f8nb11ebc28dc55f811@mail.gmail.com>
Date:	Thu, 27 Dec 2007 10:57:20 -0800
From:	"Russell Leidich" <rml@...gle.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, "Andi Kleen" <ak@...e.de>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...e.hu>
Subject: Re: [PATCH] AMD Thermal Interrupt Support

Thanks Andrew.  I have a few questions on your comments...

On Dec 25, 2007 2:04 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > +     unsigned int apic_lv_therm;
> > +
> > +     /* Set up APIC_LVTTHMR to issue THERMAL_APIC_VECTOR. */
> > +     apic_lv_therm = apic_read(APIC_LVTTHMR);
> > +     /*
> > +      * See if some agent other than this routine has already initialized
> > +      * APIC_LVTTHMR, i.e. if it's unmasked, but not equal to the value that
> > +      * we would have programmed, had we been here before on this core.
> > +      */
> > +     if ((!(apic_lv_therm & APIC_LVT_MASKED)) && ((apic_lv_therm &
> > +             (APIC_MODE_MASK | APIC_VECTOR_MASK)) != (APIC_DM_FIXED |
> > +             THERMAL_APIC_VECTOR))) {
> > +             unsigned int cpu = smp_processor_id();
>
> afaict this function is called while the calling thread is running
> preemptibly.  This smp_processor_id() call should have generated a runtime
> warning if it was tested with all debug options enabled?

I thought that the whole point of on_each_cpu(&thermal_apic_init,
NULL, 1, 0) was to ensure that thermal_apic_init() runs
(nonpreemptibly) on each core.  No?

> > +static void default_smp_thermal_interrupt(void) {}
>
> static void default_smp_thermal_interrupt(void)
> {
> }
>
> please.
>
>
> Can this function ever actually be called?

My colleauge was concerned that we have a do-nothing handler in case
we get a spurious thermal interrupt.  In my view, there's no point
programming for the possibility of broken hardware.  On the other
hand, I do need some sort of indirection to bind the entry.S thermal
handler from assembly language to either Intel or AMD C code.  Trouble
is, at compiletime, we might have both Intel and AMD support
installed, but only one of them should actually receive the interrupt
at runtime.  So I think I need to do runtime binding, unless I want to
do CPUID inside the ISR.  What do you think?

-- 
Russell Leidich
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