drm/i915: IBX has a fixed pch pll to pch pipe mapping

This should fix breakage introduced in

commit ee7b9f9
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Fri Apr 20 17:11:53 2012 +0100

    drm/i915: manage PCH PLLs separately from pipes

v2: Add a DRM_DEBUG_KMS message to explain why a given pll was
selected, suggested by Chris Wilson.

v3: Actually run git add.

Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=49712
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -2911,6 +2911,17 @@ static struct intel_pch_pll *intel_get_pch_pll(struct intel_crtc *intel_crtc, u3
 		goto prepare;
 	}
 
+	if (HAS_PCH_IBX(dev_priv->dev)) {
+		/* Ironlake PCH has a fixed PLL->PCH pipe mapping. */
+		i = intel_crtc->pipe;
+		pll = &dev_priv->pch_plls[i];
+
+		DRM_DEBUG_KMS("CRTC:%d using pre-allocated PCH PLL %x\n",
+			      intel_crtc->base.base.id, pll->pll_reg);
+
+		goto found;
+	}
+
 	for (i = 0; i < dev_priv->num_pch_pll; i++) {
 		pll = &dev_priv->pch_plls[i];