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

[Anders Kaseorg]

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?

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?

Anders