linux-kernel - Re: [GIT PULL] ACPI and power management fixes for v3.11-rc4

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Message-ID: <CAMP44s1Knox3oVt3-ePkDHxa2uNQAFVFRwmVTATNknWA46b_Uw@mail.gmail.com>
Date:	Fri, 2 Aug 2013 20:48:09 -0500
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [GIT PULL] ACPI and power management fixes for v3.11-rc4

On Fri, Aug 2, 2013 at 5:21 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Friday, August 02, 2013 04:31:37 PM Felipe Contreras wrote:
>> On Fri, Aug 2, 2013 at 4:21 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> > On Friday, August 02, 2013 02:12:49 PM Felipe Contreras wrote:
>>
>> >> You forgot this patch:
>> >>
>> >> https://git.kernel.org/cgit/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=3706231332d57072e0e2c0e59975443f3f18e673
>> >>
>> >> Or do you think it's fine to boot these machines into a black screen?
>> >
>> > Seriously, what's wrong with you?!
>> >
>> > I didn't forget about it, I just didn't include it into this particular
>> > pull request.
>> >
>> > And I'm not even sure I will push it for 3.11, because I prefer to revert
>> > efaa14c for 3.11 if that's necessary to make your broken box work as before.
>>
>> The issue happens in more than just "my broken box", and yes,
>> reverting that patch would help (in more than just my box), in the
>> sense that at least Linux won't boot into a black screen.
>>
>> But the backlight control still wouldn't work, as it hasn't worked
>> since v3.7, possibly in many ASUS laptops, for that you need more than
>> just reverting efaa14c.
>
> Yes, last time it worked in 3.6 and in particular it doesn't work in 3.10.
> My current goal is bring things back to the 3.10 state first, possibly without
> introducing any new problems, because we're kind of late in the cycle.
> That's better done by reverting stuff known to have introduced problems in
> the first place and not by doing things that may introduce more of them.
>
> And your blacklisting patch has potential to introduce problems.  Your goal is
> to bring backlight control to the 3.6 state on that particular machine, but
> the blacklist is done at the *system* level and very well may affect more
> things than just backlight.  You may not see any problems resulting from it
> and you may not care even if there are some, but other users of it may use
> different user space, for example, and may see problems that you're not seeing.
>
> That's why I'd very much prefer to do the revert at this point.

Yes, that's fine, either the revert, or the patch I mentioned, or
something else, but something has to be done, and it was better to do
it in v3.11-rc4 than in v3.11-rc5, because that change itself can
cause further problems.

>> > Well, perhaps I just won't push it at all so that you actually can go and
>> > complain to Linus about that ...
>>
>> That is very responsible from you. Screw the users, right?
>
> No, that's not my goal, sorry for disappointing you.
>
> The problem is that I'm not really convinced about the validity of the
> blacklisting approach to begin with.  As I said, the blacklisting is done
> on the system level and the goal is to work around backlight control problems.
> That sounds like a sledgehammer approach to me, which I don't really like.
> If the blacklisting was more targeted, done at the video driver level etc.,
> I wouldn't really have any concerns about it, but that's not the case.
>
> And since people evidently could live for over 6 months with the backlight
> control problems, maybe they'll survive some more time still and allow us to
> find a better approach?

They probably can survive without Linux at all, that doesn't mean we
are doing our job.

Let's do a though experiment, let's say you are right, and they can
survive the 6 months it would take you to find the "perfect" solution,
say in v3.13. What's wrong with having a partial solution in v3.12? If
the blacklisting doesn't work properly (there's absolutely no evidence
for that), then you revert it on v3.12.1.

What's wrong with that approach?

-- 
Felipe Contreras
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