drm/i915: Initialize CHV digital lock detect threshold

Initialize lock detect threshold and select coarse threshold for the
case where M2 fraction division is disabled.

v2: Split the changes into multiple smaller patches (Ville)
v3: Clear out the old bits before we modify those bits as RMW (Ville)
v4: Reset coarse threshold when M2 fraction is enabled (Ville)

Signed-off-by: Vijay Purushothaman <vijay.a.purushothaman@linux.intel.com>
Reviewed-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 8676cb8..2eea258 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6207,6 +6207,15 @@
 		dpio_val |= DPIO_CHV_FRAC_DIV_EN;
 	vlv_dpio_write(dev_priv, pipe, CHV_PLL_DW3(port), dpio_val);
 
+	/* Program digital lock detect threshold */
+	dpio_val = vlv_dpio_read(dev_priv, pipe, CHV_PLL_DW9(port));
+	dpio_val &= ~(DPIO_CHV_INT_LOCK_THRESHOLD_MASK |
+					DPIO_CHV_INT_LOCK_THRESHOLD_SEL_COARSE);
+	dpio_val |= (0x5 << DPIO_CHV_INT_LOCK_THRESHOLD_SHIFT);
+	if (!bestm2_frac)
+		dpio_val |= DPIO_CHV_INT_LOCK_THRESHOLD_SEL_COARSE;
+	vlv_dpio_write(dev_priv, pipe, CHV_PLL_DW9(port), dpio_val);
+
 	/* Loop filter */
 	refclk = i9xx_get_refclk(crtc, 0);
 	loopfilter = 5 << DPIO_CHV_PROP_COEFF_SHIFT |