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

Takashi Iwai
2011-11-20T11:22:52Z

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@suse.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