Re: [Ksummit-discuss] [TECH TOPIC] System-wide interface to specify the level of PM tuning

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Tue, Jul 21, 2015 at 12:21 AM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> On Friday, July 17, 2015 01:41:56 PM Daniel Vetter wrote:
>> On Thu, Jul 16, 2015 at 5:58 PM, Greg KH <greg@kroah.com> wrote:
>> > On Thu, Jul 16, 2015 at 08:53:02AM -0700, Josh Triplett wrote:
>> >> But the kernel already has quirk tables for various hardware, and that
>> >> seems appropriate to continue putting in the kernel.
>> >
>> > For some types of devices, sure.  For others, like broken USB keyboards
>> > that can't handle autosuspend, no.  For those we need a userspace
>> > _whitelist_ that udev can use.  So there's no one answer that works for
>> > all types of quirks.
>>
>> Whether white or blacklist or some other mixed thing doesn't really
>> matter. Imo the important part is that driver maintainers are in the
>> best position to maintain that, and pushing it out to anyone else is
>> just really not doing our jobs. And I think for most of these quirk
>> lists the kernel does seem like the most appropriate place. If the
>> list becomes giantic then we can move it to userspace (if that's
>> really a problem, afaik no one proposed yet to move device match
>> tables into userspace either and that's kinda the same thing really).
>> But as long as there's no white/black/whatever list yet starting in
>> the kernel is imo the right place.
>
> Well, I'm wondering, then, why i915.enable_psr is not enabled by default,
> for one example?
>
> Failing to enable it prevents some SoCs from using the deepest available
> C-states which in turn hurts battery life of the systems containing them
> quite a bit, so there surely is a reason to have it enabled.

Because it's broken on a lot of machines, and it takes a pile of
effort to fix it. That work is under way now, but for a long time
priorities set by management where much more set on chasing the next
shiny thing. Took a few years of making noises about dropping it all
if it doesn't get fixed.

This is actually a perfect example of what I mean with "hey it works
on my machine here, but I can't be bothered to fix up the corner-cases
so let's keep it disabled and move on". And the corner cases are hung
machines and frozen displays (and a few other things), and we
inflicted that a few times on Linus even.

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch