linux-kernel - Re: [PATCH] drm/i915: Fix invalid backpanel values for GEN3 or older chips

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Date:	Sun, 20 Nov 2011 12:22:50 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Keith Packard <keithp@...thp.com>
Cc:	Daniel Mack <zonque@...il.com>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Jesse Barnes <jbarnes@...tuousgeek.org>, harald@...hat.com,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915: Fix invalid backpanel values for GEN3 or older chips

At Sat, 19 Nov 2011 10:34:12 -0800,
Keith Packard wrote:
> 
> [1  <text/plain (quoted-printable)>]
> On Sat, 19 Nov 2011 11:05:05 +0100, Takashi Iwai <tiwai@...e.de> wrote:
> 
> > Maybe it'd be better to mention that actually setting bit-0 caused a
> > blank screen on some machines.
> 
> Was that caused by *just* setting bit zero? Or was it caused by setting
> the duty cycle to 0xffff, in which case it would be larger than the
> maximum value?
> 
> I'll clean up the commit log message with your answer and then push this out.

According to Daniels' original post:

On 11/04/2011 03:36 PM, Daniel Mack wrote:
> I'm facing a bug on a Samsung X20 notebook which features an i915
> chipset (output of 'lspci -v' attached).
>
> The effect is that setting the backlight to odd values causes the value
> to be misinterpreted. Harald Hoyer (cc:) had the same thing on a Netbook
> (I don't recall which model it was).
>
> So this will turn the backlight to full brightness:
>
> # cat /sys/class/backlight/intel_backlight/max_brightness
> 29750
> # echo 29750 > /sys/class/backlight/intel_backlight/brightness
>
> However, writing 29749 will turn the display backlight off, and 29748
> appears to be the next valid lower value.

So, writing bit-0 caused a problem, as it seems.


Takashi
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