[Intel-gfx] [BUG] LVDS using single instead of dual channel mode

[Andreas Heider]

Hi,

after a lot of debugging i found the cause of the distortion described in my earlier mail ([Intel-gfx] No VBT in OpRegion / Switching MBP Arrandale):
 In intel_display.c, static const intel_limit_t *intel_ironlake_limit(struct drm_crtc *crtc) it didn't detect that the panel needed dual channel mode. 
((I915_READ(PCH_LVDS) & LVDS_CLKB_POWER_MASK) == LVDS_CLKB_POWER_UP) returns 0 after boot.

I added circumvented the check and forced dual channel mode and the problem is gone, but i doubt that's a solution that could make it into the main version of the driver.

How could this be resolved in a clean way?