linux-kernel - Re: [PATCH] kexec: reenable HPET before kexec

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Date:	Thu, 23 Aug 2007 15:49:36 +0400
From:	Konstantin Baydarov <kbaidarov@...mvista.com>
To:	vgoyal@...ibm.com
Cc:	RT <linux-rt-users@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] kexec: reenable HPET before kexec

On Thu, 23 Aug 2007 14:38:45 +0530
Vivek Goyal <vgoyal@...ibm.com> wrote:
> Does your kernel 2 boot normally? I mean through BIOS and boot-loader?
> This explanation seems to be suggesting that because PM and ACPI is
> disabled, kernel 2 does not search for HPET. If this is the case,
> this kernel will not boot even through normal boot-loader and will
> try to use PIT instead?
> 
> If so, it is not an kexec issue at all.
> 
> Thanks
> Vivek

kernel 2 boots normally through BIOS and boot-loader. I agree with your
explanation.
It seems that kernel 2 can't enable PIT, when it is executed by kexec.
As kernel 1 disabled HPET(IRQ0 source) and PIT is "broken"(or isn't
enabled) IRQ0 are not triggered at all, and kernel 2 hangs.
As kernel 2 boots normally through BIOS and boot-loader, than
additional code needed(in Linux kernel init code) for PIT or ACPI
or APIC initialization, I mean the same code as executed on BIOS stage.
I agree that it's not an kexec issue. But can we use my fix as a
workaround(to make kexec work) until PIT will be fixed?
Everything above is correct for i386/x86_64 RT(2.6.23-rc2-rt2) kernel
and for i368 "plain"(2.6.23-rc3) kernel. Bug isn't reproduced in 2.6.23-rc3
x86_64 kernel, because x86_64 code never disables HPET. So on every
boot(initiated by kexec or BIOS) IRQ0 are triggered.

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