usb: gadget: f_uac2: split out audio core

Abstract the peripheral side ALSA sound card code from
the f_uac2 function into a component that can be called
by various functions, so the various flavors can be split
apart and selectively reused.

Visible changes:
 - add uac_params structure to pass audio paramteres for
   g_audio_setup
 - make ALSA sound card's name configurable
 - add [in/out]_ep_maxpsize
 - allocate snd_uac_chip structure during g_audio_setup
 - add u_audio_[start/stop]_[capture/playback] functions

Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/Kconfig

@@ -158,6 +158,9 @@ config USB_U_SERIAL
 config USB_U_ETHER
 	tristate
 
+config USB_U_AUDIO
+	tristate
+
 config USB_F_SERIAL
 	tristate
 
@@ -381,6 +384,7 @@ config USB_CONFIGFS_F_UAC2
 	depends on SND
 	select USB_LIBCOMPOSITE
 	select SND_PCM
+	select USB_U_AUDIO
 	select USB_F_UAC2
 	help
 	  This Audio function is compatible with USB Audio Class

drivers/usb/gadget/function/Makefile

@@ -32,6 +32,7 @@ usb_f_mass_storage-y		:= f_mass_storage.o storage_common.o
 obj-$(CONFIG_USB_F_MASS_STORAGE)+= usb_f_mass_storage.o
 usb_f_fs-y			:= f_fs.o
 obj-$(CONFIG_USB_F_FS)		+= usb_f_fs.o
+obj-$(CONFIG_USB_U_AUDIO)	+= u_audio.o
 usb_f_uac1-y			:= f_uac1.o u_uac1.o
 obj-$(CONFIG_USB_F_UAC1)	+= usb_f_uac1.o
 usb_f_uac2-y			:= f_uac2.o

drivers/usb/gadget/function/u_audio.h

@@ -0,0 +1,95 @@
+/*
+ * u_audio.h -- interface to USB gadget "ALSA sound card" utilities
+ *
+ * Copyright (C) 2016
+ * Author: Ruslan Bilovol <ruslan.bilovol@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#ifndef __U_AUDIO_H
+#define __U_AUDIO_H
+
+#include <linux/usb/composite.h>
+
+struct uac_params {
+	/* playback */
+	int p_chmask;	/* channel mask */
+	int p_srate;	/* rate in Hz */
+	int p_ssize;	/* sample size */
+
+	/* capture */
+	int c_chmask;	/* channel mask */
+	int c_srate;	/* rate in Hz */
+	int c_ssize;	/* sample size */
+
+	int req_number; /* number of preallocated requests */
+};
+
+struct g_audio {
+	struct usb_function func;
+	struct usb_gadget *gadget;
+
+	struct usb_ep *in_ep;
+	struct usb_ep *out_ep;
+
+	/* Max packet size for all in_ep possible speeds */
+	unsigned int in_ep_maxpsize;
+	/* Max packet size for all out_ep possible speeds */
+	unsigned int out_ep_maxpsize;
+
+	/* The ALSA Sound Card it represents on the USB-Client side */
+	struct snd_uac_chip *uac;
+
+	struct uac_params params;
+};
+
+static inline struct g_audio *func_to_g_audio(struct usb_function *f)
+{
+	return container_of(f, struct g_audio, func);
+}
+
+static inline uint num_channels(uint chanmask)
+{
+	uint num = 0;
+
+	while (chanmask) {
+		num += (chanmask & 1);
+		chanmask >>= 1;
+	}
+
+	return num;
+}
+
+/*
+ * g_audio_setup - initialize one virtual ALSA sound card
+ * @g_audio: struct with filled params, in_ep_maxpsize, out_ep_maxpsize
+ * @pcm_name: the id string for a PCM instance of this sound card
+ * @card_name: name of this soundcard
+ *
+ * This sets up the single virtual ALSA sound card that may be exported by a
+ * gadget driver using this framework.
+ *
+ * Context: may sleep
+ *
+ * Returns zero on success, or a negative error on failure.
+ */
+int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
+					const char *card_name);
+void g_audio_cleanup(struct g_audio *g_audio);
+
+int u_audio_start_capture(struct g_audio *g_audio);
+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);
+
+#endif /* __U_AUDIO_H */

drivers/usb/gadget/legacy/Kconfig

@@ -56,6 +56,7 @@ config USB_AUDIO
 	select SND_PCM
 	select USB_F_UAC1 if GADGET_UAC1
 	select USB_F_UAC2 if !GADGET_UAC1
+	select USB_U_AUDIO if USB_F_UAC2
 	help
 	  This Gadget Audio driver is compatible with USB Audio Class
 	  specification 2.0. It implements 1 AudioControl interface,