linux-kernel - Re: [PATCH] ACPI: don't walk tables if ACPI was disabled

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Date:	Sat, 21 Jun 2008 10:19:38 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Len Brown" <lenb@...nel.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, "Zhao Yakui" <yakui.zhao@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Alexey Starikovskiy" <astarikovskiy@...e.de>,
	"Yinghai Lu" <yhlu.kernel@...il.com>,
	"Bjorn Helgaas" <bjorn.helgaas@...com>
Subject: Re: [PATCH] ACPI: don't walk tables if ACPI was disabled

On Fri, Jun 20, 2008 at 11:27 PM, Vegard Nossum <vegard.nossum@...il.com> wrote:
> So I guess this function, pnpbios_init() needs the check as well. In
> fact, it has this:
>
> #ifdef CONFIG_PNPACPI
>        if (!acpi_disabled && !pnpacpi_disabled) {
>                pnpbios_disabled = 1;
>                printk(KERN_INFO "PnPBIOS: Disabled by ACPI PNP\n");
>                return -ENODEV;
>        }
> #endif                          /* CONFIG_ACPI */
>
> ...I guess that should be changed to say if (acpi_disabled ||
> pnpacpi_disabled)? Or... I don't understand the purpose of the
> original test. But it seems to be there since the beginning of time
> (or, well, v2.6.12-rc2).

Nope. I found the introduction of the change in the historical git repository:

commit 4723ebe898a32262ed49fe677897ccea47e72ff4
Author: Adam Belay <ambx1@....rr.com>
Date:   Sun Oct 24 15:07:32 2004 -0400

    [PNPBIOS] disable if ACPI is active

    As further ACPI pnp functionaility is implemented it is no longer
    safe to run ACPI and PNPBIOS concurrently.

    We therefore take the following approach:
    - attempt to enable ACPI support
    - if ACPI fails (blacklist etc.) enable pnpbios support
    - if ACPI support is not compiled in the kernel enable pnpbios support

    Signed-off-by: Adam Belay <ambx1@....rr.com>

and now I understand the purpose of the check; pnpbios does not depend
on ACPI; ACPI/pnpacpi is incompatible with pnpbios.

Yet it remains a fact that pnpbios will discover devices which then
ACPI code uses erroneously. Which means that my original fix for Ingo
probably is the right one after all. Should I submit another patch
which does the right thing for everything under drivers/acpi/, or can
you do it on your own? :-)


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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