On Thu, Jul 16, 2015 at 2:19 AM David Woodhouse <dwmw2@infradead.org> wrote:

> On Wed, 2015-07-15 at 18:10 -0700, Josh Triplett wrote:
> >
> > > The point here is whether or not we want to have a way to make all of
> them be
> > > enabled by default instead and see what happens, for example.
> >
> > To some degree that seems like an admission of defeat: we can't possibly
> > do the right thing by default, so we give up and add a way for the user
> > to configure it.
> >
> > We should be selecting the most sensible combination of power and
> > performance by default; we should not punt that question to the average
> > user, *or* to the distros.
>
> Not to the user, perhaps. But it's not *so* unreasonable to let each of
> the distros tune things for *their* class of users. We might want base
> profiles for 'server', 'desktop' and 'laptop on battery' that distros
> work from.
>
>
We need to be able to give even the distros more help than they have now.
The problem is that the distros simply don't have the knowledge to tune
*all* the knobs appropriately.  If we gave them one knob as you suggested
(and what Rafael is suggesting) set to a sane default determined by the
kernel - they could then use whatever userspace tool to change it based on
whatever parameters they want.

But although that's complex, it's not the real problem.
>
> The real problem, as others have said, is when we have power management
> features which work fine for 99% of the population, but fail
> occasionally on broken hardware.
>
> We can't easily blacklist the known-broken devices or whitelist the
> good ones, and we end up having to turn the feature off by default.
>
> Sure, a DMI match on "HP" and "TO BE FILLED BY OEM" would often go a
> long way for a certain class of problem, but even that's not sufficient
> :)
>

driver maintainers don't want to maintain blacklist/whitelist because it's
hard.  It'd be nice to be able to load a black list or white list of
devices from the filesystem like we do with firmware.

>
>