[Intel-gfx] [PATCH 4/7] drm/i915: Add i830 "pipes power well"

[Chris Wilson]

On Thu, Jun 01, 2017 at 05:36:16PM +0300, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> 830 more or less requires both pipes and DPLLs to remain on as long
> as either pipe is needed. However, when neither pipe is actually needed,
> we can save a bit of power by turning everything off. To do that we add
> a new "power well" that turns both pipes and DPLLs on and off in the
> right order. Seems to save ~50mW on my Fujitsu-Siemens Lifebook S6010.
> 
> This also avoids having to abuse the load detection to force pipe A on
> at init time. That was never very robust, and it only worked for one
> pipe, whereas 830 really needs both pipes enabled. As a bonus the 830
> pipe quirk is now a bit more isolated from the rest of the mode setting
> infrastructure, which should mean that it's much less likely someone
> will accidentally break it in the future. The extra cost is of course
> slight code duplication, but that seems like a worthwile tradeoff here.

Defining it as a powerwell is an interesting way to do it, and seems
quite apt. My only nit is a request not to add to intel_display.c if we
can place it elsewhere, intel_gen2_pm.c ? gen2_runtime_pm.c?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre