From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH 6/6] drm/i915: set the backlight panel
 delays registers to 1
Date: Tue, 28 Jan 2014 09:02:14 +0100
Message-ID: <20140128080214.GK9772@phenom.ffwll.local>
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To: Jani Nikula <jani.nikula@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org, Paulo Zanoni <paulo.r.zanoni@intel.com>
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On Tue, Jan 28, 2014 at 09:57:57AM +0200, Jani Nikula wrote:
> On Thu, 19 Dec 2013, Paulo Zanoni <przanoni@gmail.com> wrote:
> > From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> >
> > Because we already do the wait in software: see
> > ironlake_wait_backlight_on and ironlake_edp_wait_backlight_off.
> >
> > For the "backlight on" delay, even BSpec says we need to program 0x1
> > to PP_ON_DELAYS 12:0.
> >
> > For the "backlight off" delay, if we don't do the same thing, when we
> > call ironlake_wait_panel_off we'll end up waiting for the it again.
> >
> > On my machine the off delay is 200ms, so we save this amount of time
> > whenever we disable the panel (e.g, suspend).
> 
> Whoa. This appears to fix an eDP black screen with 24->18 bpp dithering:
> 
> https://bugs.freedesktop.org/show_bug.cgi?id=73567#c21

I dunno whether I should cry or laugh ... Problem is that I don't really
see a way to port just this patch to 3.14. So we need the entire series,
which is a bit much imo. At least until we have more users scaling our
walls.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch