drm/i915/audio: extend get_saved_enc() to support more scenarios

In initialization, audio driver will call functions get_eld() and etc.
But at that time, audio driver may not know whether it is DP MST or not.
In the original function get_saved_enc(), if it is DP MST, it requires to
set the pipe to the correct value, otherwise, pipe to be -1.

Although audio driver can get the knowledge whether it is in DP MST mode
or not by reading the codec register. It will drop performance each time
before it calls the get_eld and other similar functions. As gfx driver can
easily know whether it is in DP MST mode or not. Let's extend the
get_saved_enc() function to handle the situation that audio driver
still sends the device id info even it is in DP SST mode and return
the correct intel_encoder instead of panic.

Signed-off-by: Libin Yang <libin.yang@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1480569439-54252-1-git-send-email-libin.yang@intel.com

drivers/gpu/drm/i915/intel_audio.c

@@ -737,25 +737,49 @@ static int i915_audio_component_get_cdclk_freq(struct device *kdev)
 	return dev_priv->cdclk_freq;
 }
 
+/*
+ * get the intel_encoder according to the parameter port and pipe
+ * intel_encoder is saved by the index of pipe
+ * MST & (pipe >= 0): return the av_enc_map[pipe],
+ *   when port is matched
+ * MST & (pipe < 0): this is invalid
+ * Non-MST & (pipe >= 0): only pipe = 0 (the first device entry)
+ *   will get the right intel_encoder with port matched
+ * Non-MST & (pipe < 0): get the right intel_encoder with port matched
+ */
 static struct intel_encoder *get_saved_enc(struct drm_i915_private *dev_priv,
 					       int port, int pipe)
 {
+	struct intel_encoder *encoder;
 
 	if (WARN_ON(pipe >= I915_MAX_PIPES))
 		return NULL;
 
 	/* MST */
-	if (pipe >= 0)
-		return dev_priv->av_enc_map[pipe];
+	if (pipe >= 0) {
+		encoder = dev_priv->av_enc_map[pipe];
+		/*
+		 * when bootup, audio driver may not know it is
+		 * MST or not. So it will poll all the port & pipe
+		 * combinations
+		 */
+		if (encoder != NULL && encoder->port == port &&
+		    encoder->type == INTEL_OUTPUT_DP_MST)
+			return encoder;
+	}
 
 	/* Non-MST */
-	for_each_pipe(dev_priv, pipe) {
-		struct intel_encoder *encoder;
+	if (pipe > 0)
+		return NULL;
 
+	for_each_pipe(dev_priv, pipe) {
 		encoder = dev_priv->av_enc_map[pipe];
 		if (encoder == NULL)
 			continue;
 
+		if (encoder->type == INTEL_OUTPUT_DP_MST)
+			continue;
+
 		if (port == encoder->port)
 			return encoder;
 	}