[Intel-gfx] [PATCH 2/4] drm/i915: remove combination mode for backlight control, again

[Jesse Barnes]

On Thu, 30 Aug 2012 11:29:11 +0200
"Indan Zupancic" <indan at nul.nu> wrote:

> On Tue, August 28, 2012 16:55, Daniel Vetter wrote:
> > On Tue, Aug 28, 2012 at 04:39:34PM +0200, Indan Zupancic wrote:
> >> Some backlight problems on GEN4 can be solved by not fiddling with the
> >> backlight. The current code sets the backlight to 0 to disable the panel
> >> (last year anyway, maybe the code changed), but on gen >= 4 it can do the
> >> same by clearing bit 31 in BLC_PWM_CLT2. That way the original backlight
> >> value doesn't need to be saved anywhere.
> >
> > A while back I've improved the backlight code to properly switch the pipe
> > that controls the pwm and also to properly toggle the enable bit for
> > gen4+, see the new intel_panel_enable_backlight functions. Would it be
> > correct in your opinion to simply ditch the call to
> > intel_panel_actually_set_backlight for gen4+ unconditionally? Same for
> > intel_panel_disable_backlight obviously?
> 
> Yes, that seems the whole point of having the PWM disable bit.
> 
> I would also ditch the backlight_enabled state tracking, as it's
> unnecessary and incorrect because the enable/disable calls aren't
> balanced.
> 
> I'll update my kernel to the latest git code and try out how the
> current code works and if not touching LBPC at all works for gen 2
> hardware. If it doesn't then LBPC needs to be saved/restored in
> i915_suspend.c after all.
> 
> It would be nice if backlight control worked with ASLE disabled,
> that would get rid of all complexity, including combination mode.
> Or alternatively, if disabling combination mode at boot works then
> we can get rid of the complicated brightness setting code to cope
> with it.

Did we bottom out on this discussion?  Reading through the thread I
don't see any firm conclusions, and we definitely still have bugs open
that may be resolved by this incorrect patchset...

-- 
Jesse Barnes, Intel Open Source Technology Center