From: Daniel Vetter <daniel@ffwll.ch>
To: Jani Nikula <jani.nikula@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915/vlv: hack to init backlight regs if BIOS fails to do so
Date: Wed, 25 Sep 2013 22:53:14 +0200 [thread overview]
Message-ID: <20130925205314.GP12663@phenom.ffwll.local> (raw)
In-Reply-To: <87bo3glt00.fsf@intel.com>
On Wed, Sep 25, 2013 at 08:18:39PM +0300, Jani Nikula wrote:
> On Wed, 25 Sep 2013, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> > Still digging up the actual VBT info for this, but wanted to get this
> > out there for testing, or in case others are also bugged by this.
>
> I had a look at this a few weeks back. The VBT value for max backlight
> is in Hz (as is the value you get through opregion) and transforming
> that into the value the registers eat needs some digging. I tried, but
> none of the real world examples of VBT and PWM freq matched any of that,
> so I moved on...
>
> > This can happen if you boot with an external display connected. In that
> > case, the attached eDP backlight modulation frequency may not be
> > programmed, so we need to use something (in this case the value my BIOS
> > normally programs with just the internal display enabled).
>
> Something similar is required for non-vlv ChromeOS stuff too AFAIK.
Afaik ChromeOS doesn't have a vbt, so I think we need to shovel some
failsafe (yeah, failsafe and backlight doesn't compute, I know) default
into the regs in case all else fails.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
prev parent reply other threads:[~2013-09-25 20:52 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-25 16:40 [PATCH] drm/i915/vlv: hack to init backlight regs if BIOS fails to do so Jesse Barnes
2013-09-25 17:18 ` Jani Nikula
2013-09-25 17:31 ` Jesse Barnes
2013-09-25 17:47 ` Jesse Barnes
2013-09-25 20:53 ` Daniel Vetter [this message]
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