linux-kernel - Re: [PATCH v2] Enable A20 using KBC for some MSI laptops to fix S3 resume

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Date:	Thu, 25 Oct 2012 12:00:13 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ondrej Zary <linux@...nbow-software.org>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Enable A20 using KBC for some MSI laptops to fix S3
 resume

On 10/25/2012 01:17 AM, Ondrej Zary wrote:
> On Wednesday 24 October 2012, H. Peter Anvin wrote:
>> On 10/24/2012 02:16 PM, Ondrej Zary wrote:
>>> Some MSI laptop BIOSes are broken - INT 15h code uses port 92h to enable
>>> A20 line but resume code assumes that KBC was used.
>>> The laptop will not resume from S3 otherwise but powers off after a while
>>> and then powers on again stuck with a blank screen.
>>>
>>> Fix it by enabling A20 using KBC. Affected laptop list and DMI data are
>>> from bug reports at Ubuntu Launchpad.
>>>
>>> Also add kernel parameter to easily activate this quirk on any system.
>>>
>>> Only compile tested. The original patch was tested with EX600 and PR200.
>>>
>>> Fixes https://bugzilla.kernel.org/show_bug.cgi?id=12878
>>
>> Are we guaranteed that this executes *before* the keyboard driver
>> initializes?  If not, this needs to use the i8042 interface in the input
>> subsystem or at least acquire i8042_lock.
>>
>> 	-hpa
> 
> The code is called in:
> start_kernel()->setup_arch()->acpi_boot_table_init()
> 
> I think that it's before any drivers are initialized.
> 

Yes, that is very early indeed.  Could you please, however, put in a
comment that this is safe specifically because it is invoked long before
the i8042 driver can possibly initialize?

	-hpa


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