Date: Thu, 14 Aug 2003 22:40:02 +0100
From: Jamie Lokier <jamie@shareable.org>
To: Mikael Pettersson <mikpe@csd.uu.se>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Ruben Puettmann <ruben@puettmann.net>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: 2.4.22 APM problems with IBM Thinkpad's
Message-ID: <20030814214002.GB12420@mail.jlokier.co.uk>
References: <20030813123119.GA25111@puettmann.net> <16186.14686.455795.927909@gargle.gargle.HOWL> <1060783884.8008.64.camel@dhcp23.swansea.linux.org.uk> <20030814173327.GB10889@mail.jlokier.co.uk> <16187.60175.449778.748247@gargle.gargle.HOWL>
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Mikael Pettersson wrote:
> Jamie Lokier writes:
>  > Alan Cox wrote:
>  > > On Mer, 2003-08-13 at 14:13, Mikael Pettersson wrote:
>  > > > With APIC support enabled (SMP or UP_APIC), APM must be constrained:
>  > > > DISPLAY_BLANK off
>  > > > CPU_IDLE off
>  > > > built-in driver, not module
>  > > 
>  > > This isnt sufficient because some of the SMM traps off the FN-key 
>  > > sequences also crash thinkpads if APIC is enabled. Basically *dont use
>  > > local apic* except on SMP.
>  > 
>  > Is it feasible to disable the APIC during BIOS calls,?
> 
> I don't think so.
> One problem is that BIOS calls can be very frequent (one every time
> the kernel calls pm_idle, if CPU_IDLE=y, and one each time one of those
> battery-monitoring applets feels like polling the battery status).
>
> Each time we'd have to go through a full lapic_suspend/lapic_resume
> cycle, like we do now for PM suspends, and each time the local APIC
> timer would lose ticks.

That'll just be another way of losing ticks, then :)

> And in an UP_IOAPIC system we'd better disable
> and reenable the I/O-APIC too (or reprogram it to PIC mode, but that's
> horrible). Not pretty.
> 
> Personally I'd prefer checks in apm.c that cause it to refuse to do
> any BIOS calls except at suspend or poweroff.

I'd prefer that if APM idle or blanking are enabled, the default
interrupt mode is to not use the APIC.

Saving power is pretty desirable on a laptop.

-- Jamie
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