ALSA: hda - allow a codec to control the link power

A flag "link_power_control" is added to indicate whether a codec needs to
control the link power.  And a new bus ops link_power() is defined for the
codec to request to enable/disable the link power.

Signed-off-by: Mengdong Lin <mengdong.lin@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/hda/hdac_device.c

@@ -552,6 +552,21 @@ void snd_hdac_power_down_pm(struct hdac_device *codec)
 EXPORT_SYMBOL_GPL(snd_hdac_power_down_pm);
 #endif
 
+/*
+ * Enable/disable the link power for a codec.
+ */
+int snd_hdac_link_power(struct hdac_device *codec, bool enable)
+{
+	if  (!codec->link_power_control)
+		return 0;
+
+	if  (codec->bus->ops->link_power)
+		return codec->bus->ops->link_power(codec->bus, enable);
+	else
+		return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(snd_hdac_link_power);
+
 /* codec vendor labels */
 struct hda_vendor_id {
 	unsigned int id;