linux-kernel - Re: [PATCH] x86: update mptable v7

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Date:	Wed, 18 Jun 2008 21:32:01 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"Len Brown" <lenb@...nel.org>, "Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: update mptable v7

"Yinghai Lu" <yhlu.kernel@...il.com> writes:

> On Wed, Jun 18, 2008 at 5:33 PM, Len Brown <lenb@...nel.org> wrote:
>>
>>
>> On Wed, 18 Jun 2008, Yinghai Lu wrote:
>>
>>> On Wed, Jun 18, 2008 at 3:18 PM, Len Brown <lenb@...nel.org> wrote:
>>> >
>>> >
>>> > On Sun, 1 Jun 2008, Yinghai Lu wrote:
>>> >
>>> >>
>>> >> make mptable to be consistent to acpi routing, so we could
>>> >> 1. kexec kernel with acpi=off
>>> >> 2. workaround BIOS that acpi routing is working, but mptable is not right.
>>> >> so can use kernel/kexec to start other os that doesn't have good acpi
> support
>>> >
>>> > Is this an effort to boot an ACPI-mode kernel,
>>> > and then kexec a non-ACPI kernel?
>>>
>>> Yes,
>>
>> Why is this feature needed?
>> There are a number of ways that the resulting kernel may fail,
>> all platform specific.
>
> other os still doesn't have update acpi irq routing support. but has
> broken mptable.

Which is at least in part a reason to go back to the BIOS manufacturer
and get them to fix their table.

I can see a warning coming from the kernel if these two tables are inconsistent
though.

>>> > Doing so could confuse the heck out of the platform firmware,
>>> > which will think that an ACPI-mode kernel is still running.
>>> >
>>> > Note that it is a historic artifact, now considered a bug,
>>> > that ACPI uses the MPS code.  We should be divorcing these
>>> > two bodies of code rather than mixing them further.
>>>
>>> how about adding config option to not compile mptable related info?
>>
>> That's the idea.
>> CONFIG_MPS=n CONFIG_ACPI=y should build and run on
>> every PC built in this century.
>>
>> This was prototyped a long while back, but the
>> tree has churned so much since then the old
>> prototype is worthless.
>
> will look at it tonight.
>
> when EFI is popular, there is no reason to compile mps related stuff
> in kernel again. esp for 64 bit.

? EFI has nothing to do with this.  ACPI is popular today and EFI preserves
EFI.

> BTW, it is funny that Suse still has fallsafe boot entry with acpi=off.

Silly question.  Given that even writing to this table is platform specific.
Any chance we can do this any a userspace utility writing through /dev/mem
for the systems that need it?   We can even bundle the utility in the kexec-tools
package to make it easier to distribute.

Eric
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