linux-kernel - Re: Ask help about pre_init_apic

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Date:	Thu, 11 Sep 2014 23:59:25 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
cc:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	x86@...nel.org
Subject: Re: Ask help about pre_init_apic_IRQ0()

On Thu, 11 Sep 2014, Andy Shevchenko wrote:
> On Thu, 2014-09-11 at 16:35 +0200, Thomas Gleixner wrote:
> > On Thu, 11 Sep 2014, Andy Shevchenko wrote:
> > > On Thu, 2014-09-11 at 14:58 +0200, Thomas Gleixner wrote:
> > > []
> > > 
> > > > According to the MID code the apbt horror is only used for moorestown.
> > > > Medfield and later use the local apic timer without the apbt nonsense.
> > > > 
> > > > The best thing we can do is to drop moorestown support and get rid of
> > > > that apbt nonsense alltogether.
> > > 
> > > Alan Cox removed Moorestown (as a platform) support in 2012 IIRC.
> > > So, AFAIK you may safely remove those leftovers.
> > 
> > Good.
> >  
> > > > I don't think anyone deeply cares about it not being supported from
> > > > 3.18 on. The number of devices which sport a moorestown should be
> > > > pretty limited and the only relevant use case of those is to act as a
> > > > pocket heater with short battery life time. Its pretty pointless to
> > > > update kernels on pocket heaters except for bragging reasons.
> > > > 
> > > > If someone at Intel really thinks that we need to keep moorestown
> > > > alive for other than documentary and sentimental reasons, then we can
> > > > move the apbt setup to x86_init.timers.setup_percpu_clockev(). At that
> > > > point the IOAPIC is setup already, so it should just work. Untested
> > > > patch below.
> > > 
> > > Suddenly I have one priority work to do and my Medfield tablet doesn't
> > > boot by some reason. I would try to test it as soon as I can.
> > 
> > The patch wont make a difference, except you add
> 
> With patch nothing happened indeed.
> 
> 
> >      x86_intel_mid_timer=apbt_only
> 
> [    0.116839] BUG: unable to handle kernel NULL pointer dereference at
> 0000003a
> [    0.123803] IP: [<c1071c0e>] setup_irq+0xf/0x4d
> ...
> 
> > or
> >      x86_intel_mid_timer=lapic_and_apbt
> 
> [    0.116858] BUG: unable to handle kernel NULL pointer dereference at
> 0000003a
> [    0.123820] IP: [<c1071c0e>] setup_irq+0xf/0x4d
> ...
> 
> > 
> > on the kernel commandline. But even w/o that patch I doubt that
> > anything post moorestown even has that apbt trainwreck implemented. If
> > I'm right then the commandline option will prevent the thing to boot
> > at all, which is an even better reason to remove that crap
> > alltogether.
> 
> See above.

That was with the patch applied, right? What happens if you undo the
patch and add the command line options?

Thanks,

	tglx


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