drm/i915: Add reverse mapping between port and intel_encoder

This patch adds a reverse mapping from a digital port number to
intel_encoder object containing the corresponding intel_digital_port.
It simplifies the query of the encoder a lot.

Note that, even if it's a valid digital port, the dig_port_map[] might
point still to NULL -- usually it implies a DP MST port.  Due to this
fact, the NULL check in each place has no WARN_ON() and just skips the
port.  Once when the situation changes in future, we might introduce
WARN_ON() for a more strict check.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

drivers/gpu/drm/i915/intel_hdmi.c

@@ -2148,6 +2148,7 @@ void intel_hdmi_init_connector(struct intel_digital_port *intel_dig_port,
 void intel_hdmi_init(struct drm_device *dev,
 		     i915_reg_t hdmi_reg, enum port port)
 {
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_digital_port *intel_dig_port;
 	struct intel_encoder *intel_encoder;
 	struct intel_connector *intel_connector;
@@ -2216,6 +2217,7 @@ void intel_hdmi_init(struct drm_device *dev,
 		intel_encoder->cloneable |= 1 << INTEL_OUTPUT_HDMI;
 
 	intel_dig_port->port = port;
+	dev_priv->dig_port_map[port] = intel_encoder;
 	intel_dig_port->hdmi.hdmi_reg = hdmi_reg;
 	intel_dig_port->dp.output_reg = INVALID_MMIO_REG;