usb: gadget: u_audio: add bi-directional volume and mute support

USB Audio Class 1/2 have ability to change device's
volume and mute by USB Host through class-specific control
requests. Device also can notify Host about volume/mute
change on its side through optional interrupt endpoint.

This patch adds Volume and Mute ALSA controls which can be
used by user to send and receive notifications to/from
the USB Host about Volume and Mute change.

These params come from f_uac* so volume and mute controls
will be created only if the function support and enable
each explicitly
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Pavel Hofman <pavel.hofman@ivitera.com>
Link: https://lore.kernel.org/r/20210712125529.76070-3-pavel.hofman@ivitera.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/u_audio.h

@@ -19,16 +19,30 @@
  */
 #define FBACK_SLOW_MAX	250
 
+/* Feature Unit parameters */
+struct uac_fu_params {
+	int id;			/* Feature Unit ID */
+
+	bool mute_present;	/* mute control enable */
+
+	bool volume_present;	/* volume control enable */
+	s16 volume_min;		/* min volume in 1/256 dB */
+	s16 volume_max;		/* max volume in 1/256 dB */
+	s16 volume_res;		/* volume resolution in 1/256 dB */
+};
+
 struct uac_params {
 	/* playback */
 	int p_chmask;	/* channel mask */
 	int p_srate;	/* rate in Hz */
 	int p_ssize;	/* sample size */
+	struct uac_fu_params p_fu;	/* Feature Unit parameters */
 
 	/* capture */
 	int c_chmask;	/* channel mask */
 	int c_srate;	/* rate in Hz */
 	int c_ssize;	/* sample size */
+	struct uac_fu_params c_fu;	/* Feature Unit parameters */
 
 	int req_number; /* number of preallocated requests */
 	int fb_max;	/* upper frequency drift feedback limit per-mil */
@@ -49,6 +63,9 @@ struct g_audio {
 	/* Max packet size for all out_ep possible speeds */
 	unsigned int out_ep_maxpsize;
 
+	/* Notify UAC driver about control change */
+	int (*notify)(struct g_audio *g_audio, int unit_id, int cs);
+
 	/* The ALSA Sound Card it represents on the USB-Client side */
 	struct snd_uac_chip *uac;
 
@@ -94,4 +111,9 @@ void u_audio_stop_capture(struct g_audio *g_audio);
 int u_audio_start_playback(struct g_audio *g_audio);
 void u_audio_stop_playback(struct g_audio *g_audio);
 
+int u_audio_get_volume(struct g_audio *g_audio, int playback, s16 *val);
+int u_audio_set_volume(struct g_audio *g_audio, int playback, s16 val);
+int u_audio_get_mute(struct g_audio *g_audio, int playback, int *val);
+int u_audio_set_mute(struct g_audio *g_audio, int playback, int val);
+
 #endif /* __U_AUDIO_H */