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

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Message-Id: <200806250908.59315.bjorn.helgaas@hp.com>
Date:	Wed, 25 Jun 2008 09:08:58 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Zhao Yakui <yakui.zhao@...el.com>
Cc:	Vegard Nossum <vegard.nossum@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Len Brown <lenb@...nel.org>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: [PATCH] ACPI: don't walk tables if ACPI was disabled

On Tuesday 24 June 2008 07:37:37 pm Zhao Yakui wrote:
> On Tue, 2008-06-24 at 13:52 +0200, Vegard Nossum wrote:
> > On 6/24/08, Ingo Molnar <mingo@...e.hu> wrote:
> > > i havent seen the warning reappear with your fix after thousands of
> > > bootups - so i guess we can consider it fixed.
> > >
> > > Len, please consider the patch below. (it's in tip/out-of-tree)
> > 
> > No, please don't :-)
> > 
> > It fixes your particular case (the acpi_rtc_init() hunk of the patch),
> > but the acpi_walk_namespace() part should be changed to a WARN(). But
> > that is likely to cause a lot of "spurious" reports, so the other acpi
> > drivers should be fixed as well.
> In fact this issue is related with the following factors:
>    a. when acpi is disabled, OS won't initialize the ACPI mutex, which
> is accessed by many ACPI interface functions. For example:
> acpi_walk_namespace, acpi_install_fixed_event_handler.
>    b. When acpi is disabled, some drivers will call the ACPI interface
> functions. For example: The acpi_walk_namespace is called in
> dock_init/bay_init.

I think most current uses of acpi_walk_namespace() are indications
that the ACPI or PNP core is missing something.

In dock_init() and bay_init(), it's used to bind a driver to a
device.  I think it would be better if we could figure out how to
use the usual acpi_bus_register_driver() interface.  Actually, it
looks like this is already 90% done: acpi_dock_match() does the
same thing as is_dock(), so it looks like dock_init() could easily
be converted to register as a driver for ACPI_DOCK_HID.

bay_init() looks similar, with acpi_bay_match(), is_ejectable_bay(),
ACPI_BAY_HID, etc.

Other users of acpi_walk_namespace() are often to install notify
handlers to deal with add/remove events.  I think these are telling
us that we need to implement the "TBD: Handle device insertion/removal"
pieces in acpi_bus_check_device().

> The acpi_install_fixed_event_handler is called in 
> the acpi_rtc_init.

Yes (via rtc_wake_setup()).  I think this should be moved into the
RTC driver itself.  I have some ideas on how to do this; I'll post
a patch in a few days.  But for 2.6.26, I think the minimal fix of
checking acpi_disabled in acpi_rtc_init() is better.

Bjorn

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