[Intel-gfx] PROBLEM: Native backlight regressed from logarithmic to linear scale

[Daniel Vetter]

On Tue, Jul 29, 2014 at 06:14:16AM -0400, Anders Kaseorg wrote:
> On Tue, 29 Jul 2014, Hans de Goede wrote:
> > I've been thinking a bit about this, and I believe that the right answer 
> > here is to do the linear to logarithmic mapping in user-space. The intel 
> > backlight interface has a type of raw, clearly signalling to userspace 
> > that it is a raw "untranslated" interface, as such any fanciness such as 
> > creating a logarithmic scale should be done in userspace IMHO.
> 
> I was going to respond that the kernel does its own brightness stepping 
> when userspace isn’t paying attention.  But apparently only acpi_video 
> does that, and intel_backlight does not; my brightness keys now have no 
> effect outside of the X server.  Is that the expected behavior?

Userspace on linux is supposed to catch brightness keys and update the
backlight. Some acpi drivers do funny stuff behind everyone's back, but
generally that's the expected behavior. You'd need a deamon for the
backlight to work on the console.

> In any case, if you think punting part of the problem to userspace is the 
> right answer, then to flesh out the details: do you think it’s right for 
> userspace to assume that any backlight with type ‘raw’ is a linear scale 
> that needs to be converted, and one with type ‘firmware’ or ‘platform’ has 
> already been converted appropriately?

I don't think you can generally assume anything - what we do is send the
pwm signal, how linearly that translates into brightness is totally panel
and driver dependent. So no matter what you pick someone will complain I
think.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch