Comment 21 for bug 1251065

Out of curiosity more than anything else, can you try

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 27300d6b583b..eb2fa4b89219 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5548,6 +5548,8 @@ static void gen3_init_clock_gating(struct drm_device *dev)
        if (IS_PINEVIEW(dev))
                I915_WRITE(ECOSKPD, _MASKED_BIT_ENABLE(ECO_GATING_CX_ONLY));

+ I915_WRITE(DSPCLK_GATE_D, I915_READ(DSPCLK_GATE_D) | DPLUNIT_CLOCK_GATE_DISABLE);
+
        /* IIR "flip pending" means done if this bit is set */
        I915_WRITE(ECOSKPD, _MASKED_BIT_DISABLE(ECO_FLIP_DONE));
 }

and see if that cures the random lines?