[igt-dev] [RFC i-g-t 1/1] i915/pm_backlight: turn on dpms before backlight fade out and fade in

[Chegondi, Harish]

On Thu, 2019-03-14 at 07:46 +0000, Chris Wilson wrote:
> Quoting Harish Chegondi (2019-03-14 06:41:48)
> > backlight fade with suspend test turns off dpms which turns off
> > the edp backlight and panel. Then it does a runtime suspend,
> > system suspend and resume. After resume, it does a fade out and
> > fade in of the backlight brightness. From the dmesg logs of the
> > ci tests it appears that the test is setting the brightness
> > even before the edp panel and backlight are turned on resuilting
> > in the brightness values written and read to be different.
> > Turn on the dpms which turns on the edp panel and backlight
> > before backlight fade out and fade in. With this change the
> > fade_with_suspend test passes.

Chris,

My commit message was confusing. I will redo the commit message in the
next version of my patch.

> 
> But is it legal for the kernel to that? Is the kernel meant to
> restore
> the previous configuration upon resume or leave it to userspace? What
> about for fbcon?

Yes, the kernel is meant to restore the previous configuration upon
resume. In this test, before system suspend, DPMS is turned off which
sets the crtc state to inactive and edp backlight to off. After system
resume, the crtc state should still be inactive and dpms and edp
backlight should still be off. After system resume, before setting the
backlight brighness, the test should turn on the DPMS. Turning on the
DPMS would set the CRTC state to active and turn on the backlight.

-Harish.

> 
> If it is meant to leave it to userspace, why is the connector still
> even
> enabled?
> -Chris


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