drm/i915/ddi: Check transcoder instead of port when setting HDMI infoframe

The only requirement by BSpec for setting the HDMI infoframes is on DDI
platforms to do that before enabling the HDMI transcoder function, see
VIDEO_DIP_CTL bit 16. Accordingly check for the transcoder function
disabled state instead of the port's disabled state on DDI platforms.
This is needed by the next patch as it will set the infoframe during
crtc disabling where the port is still enabled.

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180613170710.15080-4-imre.deak@intel.com

drivers/gpu/drm/i915/intel_hdmi.c

@@ -59,6 +59,15 @@ assert_hdmi_port_disabled(struct intel_hdmi *intel_hdmi)
 	     "HDMI port enabled, expecting disabled\n");
 }
 
+static void
+assert_hdmi_transcoder_func_disabled(struct drm_i915_private *dev_priv,
+				     enum transcoder cpu_transcoder)
+{
+	WARN(I915_READ(TRANS_DDI_FUNC_CTL(cpu_transcoder)) &
+	     TRANS_DDI_FUNC_ENABLE,
+	     "HDMI transcoder function enabled, expecting disabled\n");
+}
+
 struct intel_hdmi *enc_to_intel_hdmi(struct drm_encoder *encoder)
 {
 	struct intel_digital_port *intel_dig_port =
@@ -834,11 +843,11 @@ static void hsw_set_infoframes(struct drm_encoder *encoder,
 			       const struct drm_connector_state *conn_state)
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->dev);
-	struct intel_hdmi *intel_hdmi = enc_to_intel_hdmi(encoder);
 	i915_reg_t reg = HSW_TVIDEO_DIP_CTL(crtc_state->cpu_transcoder);
 	u32 val = I915_READ(reg);
 
-	assert_hdmi_port_disabled(intel_hdmi);
+	assert_hdmi_transcoder_func_disabled(dev_priv,
+					     crtc_state->cpu_transcoder);
 
 	val &= ~(VIDEO_DIP_ENABLE_VSC_HSW | VIDEO_DIP_ENABLE_AVI_HSW |
 		 VIDEO_DIP_ENABLE_GCP_HSW | VIDEO_DIP_ENABLE_VS_HSW |