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

[Igor Gnatenko <i.gnatenko.brain@gmail.com>]

On Sat, 2013-08-03 at 13:54 +0200, Rafael J. Wysocki wrote:
> On Friday, August 02, 2013 08:48:09 PM Felipe Contreras wrote:
> > On Fri, Aug 2, 2013 at 5:21 PM, Rafael J. Wysocki <rjw@sisk.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@sisk.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.
> 
> A revert can be done in -rc5 just fine.  If we don't have a working fix this
> week, I'll do the revert.
> 
> > >> > 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?
> 
> If the blacklisting leads to problems, they may not be reported in the 3.12
> time frame, but much later.  For example because people won't realize that
> the problems are caused by the blacklisting until much much later.  And then
> we'll be in a spot where whatever we do will break things for someone.
> 
> And we had situations like that in the past, which is the source of my concern.
> You obviously don't have that experience, or you won't be so eager to inflict
> the blacklisting on everyone.
> 
> Anyway, as you know, but conveniently don't mention, I asked some experienced
> people for opinions about that.  If they agree with you, we will add the
> blacklist.  If they don't, we won't add it.
> 
> Rafael
> 
I am opposed to this patch. On ThinkPad X230 I had problems with it.
Felipe, come over to dark side. They have cookies.
-- 
Igor Gnatenko
Fedora release 19 (Schrödinger’s Cat)
Linux 3.10.4-300.fc19.x86_64