drm/i915: Tolerate bogus DPLL selection

Let's check that we actually found the PLL before doing the
port_clock readout, just in case the hardware was severly
misprogrammed by the previous guy. Not sure the hw would
even survive such misprogramming without hanging but no
real harm in checking anyway.

Cc: Karthik B S <karthik.b.s@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210310194351.6233-1-ville.syrjala@linux.intel.com
Reviewed-by: Karthik B S <karthik.b.s@intel.com>

drivers/gpu/drm/i915/display/intel_ddi.c

@@ -3716,6 +3716,9 @@ void intel_ddi_get_clock(struct intel_encoder *encoder,
 	struct icl_port_dpll *port_dpll = &crtc_state->icl_port_dplls[port_dpll_id];
 	bool pll_active;
 
+	if (drm_WARN_ON(&i915->drm, !pll))
+		return;
+
 	port_dpll->pll = pll;
 	pll_active = intel_dpll_get_hw_state(i915, pll, &port_dpll->hw_state);
 	drm_WARN_ON(&i915->drm, !pll_active);
@@ -3754,16 +3757,17 @@ static void icl_ddi_combo_get_config(struct intel_encoder *encoder,
 	intel_ddi_get_config(encoder, crtc_state);
 }
 
-static void icl_ddi_tc_get_config(struct intel_encoder *encoder,
-				  struct intel_crtc_state *crtc_state)
+static void icl_ddi_tc_get_clock(struct intel_encoder *encoder,
+				 struct intel_crtc_state *crtc_state,
+				 struct intel_shared_dpll *pll)
 {
 	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
 	enum icl_port_dpll_id port_dpll_id;
 	struct icl_port_dpll *port_dpll;
-	struct intel_shared_dpll *pll;
 	bool pll_active;
 
-	pll = icl_ddi_tc_get_pll(encoder);
+	if (drm_WARN_ON(&i915->drm, !pll))
+		return;
 
 	if (intel_get_shared_dpll_id(i915, pll) == DPLL_ID_ICL_TBTPLL)
 		port_dpll_id = ICL_PORT_DPLL_DEFAULT;
@@ -3783,7 +3787,12 @@ static void icl_ddi_tc_get_config(struct intel_encoder *encoder,
 	else
 		crtc_state->port_clock = intel_dpll_get_freq(i915, crtc_state->shared_dpll,
 							     &crtc_state->dpll_hw_state);
+}
 
+static void icl_ddi_tc_get_config(struct intel_encoder *encoder,
+				  struct intel_crtc_state *crtc_state)
+{
+	icl_ddi_tc_get_clock(encoder, crtc_state, icl_ddi_tc_get_pll(encoder));
 	intel_ddi_get_config(encoder, crtc_state);
 }