linux-kernel - Re: [REGRESSION 3.14-rc6] Samsung N150 lid does not "open" after suspend to RAM.

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Date:	Wed, 26 Mar 2014 23:41:38 +0100
From:	Stefan Biereigel <stefan@...reigel.de>
To:	Kieran Clancy <clancy.kieran@...il.com>
CC:	Juan Manuel Cabo <juanmanuel.cabo@...il.com>,
	Stefan Biereigel <security@...reigel-wb.de>,
	Lan Tianyu <lantianyu1986@...il.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r kernel org" <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	San Zamoyski <san@...snet.pl>,
	"D. Jansen" <dennis.jansen@....de>,
	Maurizio D'Addona <mauritiusdadd@...il.com>
Subject: Re: [REGRESSION 3.14-rc6] Samsung N150 lid does not "open" after
 suspend to RAM.


Am 26.03.2014 23:36, schrieb Kieran Clancy:
> On Thu, Mar 27, 2014 at 6:26 AM, Stefan Biereigel <stefan@...reigel.de> wrote:
>> I tested both of your patches. The processing of events works well on my
>> N150, the lid is reported open correctly after resume.
>> For the second patch (the whitelisting-approach), I had to change the
>> Product Name to "N150/N210/N220" instead of "N150P", because that is
>> what dmidecode reports for my netbook.
> That was quick - thanks for testing!
>
> For the product name match then, it matches substrings not whole
> strings, so "N150" should be sufficient (my mistake putting P on the
> end).
Alright, so that was the problem why it did not work with your original 
patch, but I missed that it did substring matching, so "N150" should be 
ok there.
>
>> So, all three approaches work equally well for me (whitelisting my
>> broken N150, blacklisting the broken Series 5/7/9, processing all the
>> stale events). I personally would prefer a solution which needs to
>> handle (best case) no custom cases, because there are always n+1 of
>> them. But, as I don't know if there may be any problems with the
>> approach that needs no special handling (processing all stale events) in
>> the future, I'm not the one to decide the correct solution.
> I won't be able to test ec_clear_process patch until tomorrow because
> I have a full day today.
>
> On my machine, _QXX events are all something like:
>
> if (AC_PLUGGED_IN) {
>      do_something();
> }
>
> So if (for example) AC_PLUGGED_IN has changed since the event was
> produced (e.g. no longer plugged in), nothing bad should happen.
> That's not necessarily a guarantee that this wouldn't introduce new
> bugs on other machines though.
>
> I think the ideal fix would be to distinguish between events which are
> "jammed" and won't be processed (like on Series 5/7/9), and events
> which will be processed normally with GPEs (N150). I am not sure how
> to do this or if it's even possible.
>
> For example, on my machine, the EC status byte (EC_SC) seems to be
> 0x29 for jammed events, which means the SCI_EVT bit is set but we
> never got/get the interrupt. On your N150, your status byte was 0x09
> which means the SCI_EVT was not set - it was not yet asking for the OS
> to attend to this.
>
> I wonder if something as simple as this would work (in acpi_ec_clear):
>
>                  if (!(acpi_ec_read_status(ec) & ACPI_EC_FLAG_SCI))
>                          break;
>                  status = acpi_ec_query_unlocked(ec, &value);
>                  if (status || !value)
>                          break;
>
> This would make it only clear events while the SCI_EVT bit is set. I
> am not sure that it would entirely remove the race condition you are
> seeing, but it might be enough to fix it.
>
> If we cant come up with a generally applicable solution, whitelisting
> is the lesser of two evils when compared with blacklisting here. A
> jammed EC won't function _at all_, while losing one or two EC events
> on boot/resume doesn't prevent future events and is easier to work
> around (though still not ideal).
You are right there, of course. Sadly, I can find nobody near me who 
owns one of the newer Samsung machines, therefore I can only contribute 
with testing on my machine. If there is anything else I could try, let 
me know.

Best wishes,
Stefan

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