linux-kernel - Re: your patch "x86, 8042: Enable A20 using KBC to fix S3 resume on some MSI laptops"

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Date:	Mon, 14 Jan 2013 09:29:38 +0100
From:	Ondrej Zary <linux@...nbow-software.org>
To:	"Jan Beulich" <JBeulich@...e.com>
Cc:	dmitry.torokhov@...il.com, hpa@...ux.intel.com,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org
Subject: Re: your patch "x86, 8042: Enable A20 using KBC to fix S3 resume on some MSI laptops"

On Monday 14 January 2013, Jan Beulich wrote:
> Ondrej,
>
> I see two problems with this patch: For one, on a system without
> i8042 the code at the place it got inserted ought to incur a stall of
> 1s (50us * I8042_CTL_TIMEOUT [10000] * 2). I believe that this
> code should not be run before i8042_controller_check() completed
> successfully, but at the very least the second call to
> i8042_command() should be conditional upon the first being
> successful (effectively halving the stall).

I believe that all PnP-capable systems without 8042 will exit with -ENODEV 
after x86_platform.i8042_detect(). Old non-PnP systems usually have 8042.

> Second, considering that enabling A20 (even if just in a fake way),
> is a core system operation, I don't think it belongs into a driver
> that is only optionally present in the kernel.

The first version of this patch added A20 enabling to early init code. But 
that could be dangerous as it was run before any 8042 detection, possibly 
breaking systems without 8042. I haven't found a better place for this.

-- 
Ondrej Zary
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