drm/i915: Don't read out port_clock on CHV when DPLL is disabled

Check whether the DPLL is even enabled before readoing out the dividers
and trying to derive port_clock on CHV. We already did this on VLV.

Also remove the comment "MIPI" comment from the VLV code since we call
this function whenever the pipe is enabled.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1458052809-23426-9-git-send-email-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -8009,8 +8009,8 @@ static void vlv_crtc_clock_get(struct intel_crtc *crtc,
 	u32 mdiv;
 	int refclk = 100000;
 
-	/* In case of MIPI DPLL will not even be used */
-	if (!(pipe_config->dpll_hw_state.dpll & DPLL_VCO_ENABLE))
+	/* In case of DSI, DPLL will not be used */
+	if ((pipe_config->dpll_hw_state.dpll & DPLL_VCO_ENABLE) == 0)
 		return;
 
 	mutex_lock(&dev_priv->sb_lock);
@@ -8106,6 +8106,10 @@ static void chv_crtc_clock_get(struct intel_crtc *crtc,
 	u32 cmn_dw13, pll_dw0, pll_dw1, pll_dw2, pll_dw3;
 	int refclk = 100000;
 
+	/* In case of DSI, DPLL will not be used */
+	if ((pipe_config->dpll_hw_state.dpll & DPLL_VCO_ENABLE) == 0)
+		return;
+
 	mutex_lock(&dev_priv->sb_lock);
 	cmn_dw13 = vlv_dpio_read(dev_priv, pipe, CHV_CMN_DW13(port));
 	pll_dw0 = vlv_dpio_read(dev_priv, pipe, CHV_PLL_DW0(port));