drm/i915: Fix ICL+ HDMI clock readout

Copy the 38.4 vs. 19.2 MHz ref clock exception from the dpll
mgr into the clock readout function as well.

v2: Refactor the code into a common function
    s/is_icl/gen11+/ (Rodrigo)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107722
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180903142841.14627-1-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/intel_ddi.c

@@ -1414,7 +1414,7 @@ static int cnl_calc_wrpll_link(struct drm_i915_private *dev_priv,
 		break;
 	}
 
-	ref_clock = dev_priv->cdclk.hw.ref;
+	ref_clock = cnl_hdmi_pll_ref_clock(dev_priv);
 
 	dco_freq = (cfgcr0 & DPLL_CFGCR0_DCO_INTEGER_MASK) * ref_clock;
 

drivers/gpu/drm/i915/intel_dpll_mgr.c

@@ -2212,6 +2212,20 @@ static void cnl_wrpll_params_populate(struct skl_wrpll_params *params,
 	params->dco_fraction = dco & 0x7fff;
 }
 
+int cnl_hdmi_pll_ref_clock(struct drm_i915_private *dev_priv)
+{
+	int ref_clock = dev_priv->cdclk.hw.ref;
+
+	/*
+	 * For ICL+, the spec states: if reference frequency is 38.4,
+	 * use 19.2 because the DPLL automatically divides that by 2.
+	 */
+	if (INTEL_GEN(dev_priv) >= 11 && ref_clock == 38400)
+		ref_clock = 19200;
+
+	return ref_clock;
+}
+
 static bool
 cnl_ddi_calculate_wrpll(int clock,
 			struct drm_i915_private *dev_priv,
@@ -2251,14 +2265,7 @@ cnl_ddi_calculate_wrpll(int clock,
 
 	cnl_wrpll_get_multipliers(best_div, &pdiv, &qdiv, &kdiv);
 
-	ref_clock = dev_priv->cdclk.hw.ref;
-
-	/*
-	 * For ICL, the spec states: if reference frequency is 38.4, use 19.2
-	 * because the DPLL automatically divides that by 2.
-	 */
-	if (IS_ICELAKE(dev_priv) && ref_clock == 38400)
-		ref_clock = 19200;
+	ref_clock = cnl_hdmi_pll_ref_clock(dev_priv);
 
 	cnl_wrpll_params_populate(wrpll_params, best_dco, ref_clock, pdiv, qdiv,
 				  kdiv);

drivers/gpu/drm/i915/intel_dpll_mgr.h

@@ -344,5 +344,6 @@ void intel_dpll_dump_hw_state(struct drm_i915_private *dev_priv,
 			      struct intel_dpll_hw_state *hw_state);
 int icl_calc_dp_combo_pll_link(struct drm_i915_private *dev_priv,
 			       uint32_t pll_id);
+int cnl_hdmi_pll_ref_clock(struct drm_i915_private *dev_priv);
 
 #endif /* _INTEL_DPLL_MGR_H_ */