linux-kernel - Re: [PATCH] acpi: Avoid dropping rapid hotkey events (or other GPEs) on Asus EeePC

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Date:	Wed, 13 Aug 2008 12:51:06 +0100
From:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Alexey Starikovskiy <astarikovskiy@...e.de>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	hmh@....eng.br, Maximilian Engelhardt <maxi@...monizer.de>,
	stable@...nel.org
Subject: Re: [PATCH] acpi: Avoid dropping rapid hotkey events (or other GPEs)
 on Asus EeePC

[Dupe apology: CC'd to stable@...nel.org, with the right address this time]

Andrew Morton wrote:
> On Wed, 13 Aug 2008 11:21:10 +0100 Alan Jenkins <alan-jenkins@...fmail.co.uk> wrote:
>
>   
>> Andrew Morton wrote:
>>     
>>> Did this get fixed yet?
>>>
>>> I have an patch in -mm which I just restored (I had to tempdrop it
>>> because the acpi tree was busted for some time).  But it seems to be
>>> old.
>>>
>>> http://bugzilla.kernel.org/show_bug.cgi?id=10919 is marked "resolved"
>>> but the reporter (Maximilian) seems to think otherwise.  2.6.26.x is,
>>> afaik, still unfixed, as is 2.6.27-rc.
>>>   
>>>       
>> That's correct.  I think this specific patch should go in 2.6.27 and
>> 2.6.26-stable.  No objections have been raised so far.
>>
>> I still need this patch to make my brightness and volume control keys
>> usable in 2.6.27-rc3.  (They auto-repeat fast enough to trigger the
>> bug).  This is true even after applying the latest patches from bug
>> 10919 (#25 + #27).
>>
>>     
>
> Confusing.  Please send the patch which you think we should apply.
>
>   
>> I think the 10919 fix makes it harder to reproduce, but it definitely
>> still happens.  I guess this is because the polling-driven EC
>> transactions add 1ms delays between each byte.  The slower timings leave
>> a window where the buggy behaviour of my EC can make a difference.  (It
>> has been seen to clear the "pending event" bit after a single event is
>> read, despite having more events pending).
>>
>> There are more serious consequences of this bug.  After a while it can
>> confuse the EC enough to cause lockups or reboots during boot, or after
>> pressing a single hotkey.  This bad state is preserved over reboots,
>> even into known good kernels.  Fortunately the badness clears when power
>> is removed for a long enough period.  For a while I was worried that
>> something had physically burnt out.
>>     
>
> Oh gad.  And there's no workaround?
>
Sorry, that was confusing.

The patch in currently in -mm _is_ the workaround for this damage.  It
was not initially obvious just how important it was :-).  I've
re-attached it as requested.

10919, "laggy hotkeys" is just what it says; ACPI EC events are slower
because of polling.  It appears to be a more cosmetic issue which is
orthogonal to the _dropping_ of events.

Thanks
Alan


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