[Intel-gfx] Thinkpad T420 and single/dual channel lvds
ajax at redhat.com
Wed Mar 14 11:09:19 PDT 2012
On Wed, 2012-03-14 at 17:44 +0100, Takashi Iwai wrote:
> At Wed, 14 Mar 2012 10:45:06 -0400,
> Adam Jackson wrote:
> > There may or may not be a bit for this in the VBT in the BIOS. But the
> > more reliably correct thing I suspect would be to just look at the
> > preferred mode for the panel and assume it's dual-link LVDS if the pixel
> > clock is >112MHz, since that's the crossover frequency.
> Coincidently, we hit the same issue with a HP laptop, and wondered how
> is the best way to fix. I hoped BIOS could handle better,
> i.e. setting the power bits no matter whether the lid is opened or
> not. But it doesn't set unless the lid is once opened.
> (Interestingly, the bits remain even if you close the lid again before
> booting. Just opening once seems triggering the probing of LVDS
> panel in BIOS and let it setting the right values.)
> FWIW, when I check ironalke_crtc_mode_set(), the clock of the HD+
> LVDS mode (1600x900) is 107800 (refclk 120000), while a similar
> machine with a HD panel (1366x768) shows 76300. So, I'm not sure
> whether 112MHz could be a right threshold.
Hm, fair point.
Would be interesting to compare the VBTs between the two boots. The
lvds_fp_timing struct might actually have the data we want here
regardless of how the machine booted.
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