linux-kernel - Re: [RFC][RFT][PATCH] ACPI: Protection from suspending in the middle of EC transaction

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Date:	Sun, 31 Jan 2010 19:09:20 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Alan Jenkins <sourcejedi.lkml@...glemail.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Len Brown <lenb@...nel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Thomas Renninger <trenn@...e.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][RFT][PATCH] ACPI: Protection from suspending in the
 middle  of EC transaction

On Sun, 2010-01-31 at 14:11 +0000, Alan Jenkins wrote: 
> On 1/30/10, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > Hi,
> >
> > While Maxim is testing if the patch below helps with
> > http://bugzilla.kernel.org/show_bug.cgi?id=14668
> > I think it's necessary anyway.
> >
> > The problem is that currently there's nothing to prevent us from suspending
> > in
> > the middle of an EC transaction in progress, at least as far as I can see.
> > As a result, we can suspend with the ACPI global lock held or something like
> > this, which leads to problems especially for hibernation (if the resume
> > kernel
> > passes control to the image kernel in the middle of an EC transaction,
> > things
> > aren't nice).  For this reason I think we should wait until there are no EC
> > transactions in progress before we suspend and we should prevent any new
> > EC transactions from starting after that point.  The patch below does that.

Unfortunately, this patch even causes regressions on my notebook (it
survive 63 hibernate cycles), but now I battery driver reports 'battery
absent', backlight driver reports 0 brightness, but reload helped.

I think that not only _PTS ans _WAK are problematic. What about other
ACPI drivers that start accessing the EC before it is resumed?
I think that these cause the problems I observe.

Still, at least it does resume.

Best regards,
Maxim Levitsky


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