drm/i915: clean up and simplify i9xx_crtc_mode_set wrt PLL handling

Flat out skip anything to do with PLL if we have a DSI encoder (and thus
DSI PLL). Also skip PLL computation if the encoder has already set
clocks. This allows for some tidying up of the code, including a
superfluous call to intel_limit() for LVDS downclock path.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -4918,9 +4918,12 @@ static int i9xx_crtc_mode_set(struct drm_crtc *crtc,
 		num_connectors++;
 	}
 
+	if (is_dsi)
+		goto skip_dpll;
+
+	if (!intel_crtc->config.clock_set) {
 		refclk = i9xx_get_refclk(crtc, num_connectors);
 
-	if (!is_dsi && !intel_crtc->config.clock_set) {
 		/*
 		 * Returns a set of divisors for the desired target clock with
 		 * the given refclk, or FALSE.  The returned values represent
@@ -4931,20 +4934,18 @@ static int i9xx_crtc_mode_set(struct drm_crtc *crtc,
 		ok = dev_priv->display.find_dpll(limit, crtc,
 						 intel_crtc->config.port_clock,
 						 refclk, NULL, &clock);
-		if (!ok && !intel_crtc->config.clock_set) {
+		if (!ok) {
 			DRM_ERROR("Couldn't find PLL settings for mode!\n");
 			return -EINVAL;
 		}
-	}
 
 		if (is_lvds && dev_priv->lvds_downclock_avail) {
 			/*
-		 * Ensure we match the reduced clock's P to the target clock.
-		 * If the clocks don't match, we can't switch the display clock
-		 * by using the FP0/FP1. In such case we will disable the LVDS
-		 * downclock feature.
+			 * Ensure we match the reduced clock's P to the target
+			 * clock.  If the clocks don't match, we can't switch
+			 * the display clock by using the FP0/FP1. In such case
+			 * we will disable the LVDS downclock feature.
 			 */
-		limit = intel_limit(crtc, refclk);
 			has_reduced_clock =
 				dev_priv->display.find_dpll(limit, crtc,
 							    dev_priv->lvds_downclock,
@@ -4952,7 +4953,6 @@ static int i9xx_crtc_mode_set(struct drm_crtc *crtc,
 							    &reduced_clock);
 		}
 		/* Compat-code for transition, will disappear. */
-	if (!intel_crtc->config.clock_set) {
 		intel_crtc->config.dpll.n = clock.n;
 		intel_crtc->config.dpll.m1 = clock.m1;
 		intel_crtc->config.dpll.m2 = clock.m2;
@@ -4965,7 +4965,6 @@ static int i9xx_crtc_mode_set(struct drm_crtc *crtc,
 				has_reduced_clock ? &reduced_clock : NULL,
 				num_connectors);
 	} else if (IS_VALLEYVIEW(dev)) {
-		if (!is_dsi)
 		vlv_update_pll(intel_crtc);
 	} else {
 		i9xx_update_pll(intel_crtc,
@@ -4973,6 +4972,7 @@ static int i9xx_crtc_mode_set(struct drm_crtc *crtc,
                                 num_connectors);
 	}
 
+skip_dpll:
 	/* Set up the display plane register */
 	dspcntr = DISPPLANE_GAMMA_ENABLE;