linux-kernel - Re: [BUG] 2.6.25-rc2-git8 fails to boot on 486 due to TSC breakage

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Message-ID: <18369.35401.678391.183329@harpo.it.uu.se>
Date:	Sun, 24 Feb 2008 16:16:25 +0100
From:	Mikael Pettersson <mikpe@...uu.se>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Mikael Pettersson <mikpe@...uu.se>, linux-kernel@...r.kernel.org,
	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de
Subject: Re: [BUG] 2.6.25-rc2-git8 fails to boot on 486 due to TSC breakage

Ingo Molnar writes:
 > 
 > * Mikael Pettersson <mikpe@...uu.se> wrote:
 > 
 > > The kernel for this 486 has CONFIG_M486=y and CONFIG_M586TSC=n, but 
 > > the 2.6.25 kernels still try to access the TSC. Here's the oops from 
 > > 2.6.25-rc2-git8:
 > 
 > hm, could you send me the full .config you used?

I've put it here:
<http://user.it.uu.se/~mikpe/linux/tmp/config-2.6.24-git8>

Meanwhile, I've traced the breakage to 2.6.24-git8.

2.6.24-git8 changed include/asm-x86/tsc.h:get_cycles() to call
rdtscll() even if CONFIG_X86_TSC isn't set. The call is protected
by a cpu_has_tsc test, but starting with 2.6.24-git8 cpu_has_tsc
is non-zero on this machine, which is very very wrong.

Diffing dmesg between git7 and git8 doesn't sched any light since
git8 also removed the printouts of the x86 caps as they were being
initialised and updated. I'm currently adding those printouts back
in the hope of seeing where and when the caps get broken.
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