On Wed, 2012-03-14 at 13:37 +0100, Helge Bahmann wrote: > Hi everyone, > > Booting a Thinkpad T420 with the lid closed results and opening it subsequently results in an > unusable picture on the panel (and no amount of resetting makes it usable): The even pixels show > the nominal content of the framebuffer (with the right half missing) whlie the odd pixels show a > red-/blueish flicker. > > A little bit of investigation revealed that with the lid closed on boot, the panel ends up driven in > lvds single channel mode, which the panel probably does not like. It appears that the i915 driver > relies on the BIOS setting up the PCH_LVDS register for dual channel and will otherwise not ever > consider switching. > > While the following hack makes my display work, it is quite obviously not the right thing to do -- > could you investigate if there is a "proper" way to determine whether the panel is supposed to be > driven dual channel? Nice find! 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. - ajax -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 198 bytes Desc: This is a digitally signed message part URL: <http://lists.freedesktop.org/archives/intel-gfx/attachments/20120314/5f419bee/attachment.pgp>
