linux-kernel - Re: [PATCH 27/30] ACPI: EC: Add a quirk for CLEVO M720T/M730T laptop

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Date:	Tue, 9 Oct 2012 15:19:59 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Jonathan Nieder <jrnieder@...il.com>
Cc:	Len Brown <lenb@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Brown, Len" <len.brown@...el.com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 27/30] ACPI: EC: Add a quirk for CLEVO M720T/M730T
 laptop

On Mon, 8 Oct 2012 23:59:07 -0700
Jonathan Nieder <jrnieder@...il.com> wrote:

> Feng Tang wrote:
> > Jonathan Nieder <jrnieder@...il.com> wrote:
> 
> >> What would go wrong if the threshold were just increased to 20 on all
> >> models?
> >
> > Then some other platform will stop to work.
> >	https://bugzilla.kernel.org/show_bug.cgi?id=11892 
> >
> > The 26/30 and 27/30 patches are bound together to fix one bug. Some
> > quote from description from the 26th patch:
> >
> > ACPI_EC_STORM_THRESHOLD was initially 20 when it's created, and
> > was changed to 8 in 2.6.28 commit 06cf7d3c7 "ACPI: EC: lower interrupt storm
> > threshold" to fix kernel bug 11892 by forcing the laptop in that bug to
> > work in polling mode.
> >
> > Hope this answers your question.
> 
> Thanks much.  Yes, that clarifies.
> 
> The magic numbers are not too thrilling.  If the polling mode just
> doesn't work on the Clevo M720, why isn't the appropriate storm
> threshold 999999 or infinity rather than 20?  Do we know why the
> polling mode doesn't work?

I don't know why it doesn't work, if you check the https://bugzilla.kernel.org/show_bug.cgi?id=45151 
you'll see the debugging model is
   test result --> patch --> 1-2 weeks + result --> patch
    --> 1-2 weeks + result ...
over and over, which makes it difficult to root cause it but
provide a workaround.

And frankly speaking, I'm not sure if I can figure it out 100%
even if I had that HW at hand. As per my understanding, EC is
very tricky, as OS, ACPI FW, EC FW, BIOS will all access it
without a global lock (in most cases), which makes it hard
to work properly without race condition. Not mentioning its
hardware may be broken.

Thanks,
Feng 
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