Commit cfecde435dda78248d6fcdc424bed68d5db6be0b turns screen blank

[Jeff Chua <jeff.chua.linux@gmail.com>]

The following commit causes screen to become blank. Upon boot up, screen 
becomes blank (monitor can't sync to pc) with i915 compiled in the 
kernel. With i915 as module, system boots up fine, but becomes blank as 
soon as the module is loaded.

Reverting it solves the problem. Problem only happens only Dell Optiplex 
780 with external LCD. But, works fine on Lenovo X201s internal LCD.


Thanks,
Jeff

commit cfecde435dda78248d6fcdc424bed68d5db6be0b
Author: Carl Worth <cworth@cworth.org>
Date:   Thu Apr 8 23:31:57 2010 -0700

     drm/i915: Don't enable pipe/plane/VCO early (wait for DPMS on).

     The existing code handling the DPMS ON event is much more careful to
     ensure that these registers are enabled according to strict sequencing
     requirements. Enabling these early in mode_set simply defeats that.

     Signed-off-by: Carl Worth <cworth@cworth.org>
     Signed-off-by: Eric Anholt <eric@anholt.net>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3ee68bc..243dfb8 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3463,11 +3463,6 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
  			pipeconf &= ~PIPEACONF_DOUBLE_WIDE;
  	}

-	dspcntr |= DISPLAY_PLANE_ENABLE;
-	pipeconf |= PIPEACONF_ENABLE;
-	dpll |= DPLL_VCO_ENABLE;
-
-
  	/* Disable the panel fitter if it was on our pipe */
  	if (!HAS_PCH_SPLIT(dev) && intel_panel_fitter_pipe(dev) == pipe)
  		I915_WRITE(PFIT_CONTROL, 0);