usb: gadget: u_audio: Support multiple sampling rates

Implement support for multiple sampling rates in u_audio part of the
audio gadget. The currently configured rates are exposed through
read-only amixer controls 'Capture Rate' and 'Playback Rate'.

Signed-off-by: Julian Scheel <[e-mail]>
Signed-off-by: Pavel Hofman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/gadget/function/f_uac1.c

···
 	audio->in_ep_maxpsize = le16_to_cpu(as_in_ep_desc.wMaxPacketSize);
 	audio->params.c_chmask = audio_opts->c_chmask;
 	audio->params.c_srate = audio_opts->c_srate;
+	audio->params.c_srates[0] = audio_opts->c_srate;
 	audio->params.c_ssize = audio_opts->c_ssize;
 	if (FUIN_EN(audio_opts)) {
 		audio->params.p_fu.id = USB_IN_FU_ID;
···
 	}
 	audio->params.p_chmask = audio_opts->p_chmask;
 	audio->params.p_srate = audio_opts->p_srate;
+	audio->params.p_srates[0] = audio_opts->p_srate;
 	audio->params.p_ssize = audio_opts->p_ssize;
 	if (FUOUT_EN(audio_opts)) {
 		audio->params.c_fu.id = USB_OUT_FU_ID;

drivers/usb/gadget/function/f_uac2.c

···
 
 	agdev->params.p_chmask = uac2_opts->p_chmask;
 	agdev->params.p_srate = uac2_opts->p_srate;
+	agdev->params.p_srates[0] = uac2_opts->p_srate;
 	agdev->params.p_ssize = uac2_opts->p_ssize;
 	if (FUIN_EN(uac2_opts)) {
 		agdev->params.p_fu.id = USB_IN_FU_ID;
···
 	}
 	agdev->params.c_chmask = uac2_opts->c_chmask;
 	agdev->params.c_srate = uac2_opts->c_srate;
+	agdev->params.c_srates[0] = uac2_opts->c_srate;
 	agdev->params.c_ssize = uac2_opts->c_ssize;
 	if (FUOUT_EN(uac2_opts)) {
 		agdev->params.c_fu.id = USB_OUT_FU_ID;

drivers/usb/gadget/function/u_audio.c

···
 	UAC_P_PITCH_CTRL,
 	UAC_MUTE_CTRL,
 	UAC_VOLUME_CTRL,
+	UAC_RATE_CTRL,
 };
 
 /* Runtime data params for one stream */
···
   s16 volume_min, volume_max, volume_res;
   s16 volume;
   int mute;
+
+	struct snd_kcontrol *snd_kctl_rate; /* read-only current rate */
 
   spinlock_t lock; /* lock for control transfers */
 
···
 		dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
 }
 
+int u_audio_set_capture_srate(struct g_audio *audio_dev, int srate)
+{
+	struct uac_params *params = &audio_dev->params;
+	int i;
+
+	dev_dbg(&audio_dev->gadget->dev, "%s: srate %d\n", __func__, srate);
+	for (i = 0; i < UAC_MAX_RATES; i++) {
+		if (params->c_srates[i] == srate) {
+			params->c_srate = srate;
+			return 0;
+		}
+		if (params->c_srates[i] == 0)
+			break;
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(u_audio_set_capture_srate);
+
+int u_audio_set_playback_srate(struct g_audio *audio_dev, int srate)
+{
+	struct uac_params *params = &audio_dev->params;
+	int i;
+
+	dev_dbg(&audio_dev->gadget->dev, "%s: srate %d\n", __func__, srate);
+	for (i = 0; i < UAC_MAX_RATES; i++) {
+		if (params->p_srates[i] == srate) {
+			params->p_srate = srate;
+			return 0;
+		}
+		if (params->p_srates[i] == 0)
+			break;
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(u_audio_set_playback_srate);
+
 int u_audio_start_capture(struct g_audio *audio_dev)
 {
 	struct snd_uac_chip *uac = audio_dev->uac;
···
 	struct uac_params *params = &audio_dev->params;
 	int req_len, i;
 
+	dev_dbg(dev, "start capture with rate %d\n", params->c_srate);
 	ep = audio_dev->out_ep;
 	prm = &uac->c_prm;
 	config_ep_by_speed(gadget, &audio_dev->func, ep);
···
 	int req_len, i;
 	unsigned int p_pktsize;
 
+	dev_dbg(dev, "start playback with rate %d\n", params->p_srate);
 	ep = audio_dev->in_ep;
 	prm = &uac->p_prm;
 	config_ep_by_speed(gadget, &audio_dev->func, ep);
···
 	return change;
 }
 
+static int get_max_srate(const int *srates)
+{
+	int i, max_srate = 0;
+
+	for (i = 0; i < UAC_MAX_RATES; i++) {
+		if (srates[i] == 0)
+			break;
+		if (srates[i] > max_srate)
+			max_srate = srates[i];
+	}
+	return max_srate;
+}
+
+static int get_min_srate(const int *srates)
+{
+	int i, min_srate = INT_MAX;
+
+	for (i = 0; i < UAC_MAX_RATES; i++) {
+		if (srates[i] == 0)
+			break;
+		if (srates[i] < min_srate)
+			min_srate = srates[i];
+	}
+	return min_srate;
+}
+
+static int u_audio_rate_info(struct snd_kcontrol *kcontrol,
+				struct snd_ctl_elem_info *uinfo)
+{
+	const int *srates;
+	struct uac_rtd_params *prm = snd_kcontrol_chip(kcontrol);
+	struct snd_uac_chip *uac = prm->uac;
+	struct g_audio *audio_dev = uac->audio_dev;
+	struct uac_params *params = &audio_dev->params;
+
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = 1;
+
+	if (prm == &uac->c_prm)
+		srates = params->c_srates;
+	else
+		srates = params->p_srates;
+	uinfo->value.integer.min = get_min_srate(srates);
+	uinfo->value.integer.max = get_max_srate(srates);
+	return 0;
+}
+
+static int u_audio_rate_get(struct snd_kcontrol *kcontrol,
+						 struct snd_ctl_elem_value *ucontrol)
+{
+	struct uac_rtd_params *prm = snd_kcontrol_chip(kcontrol);
+	struct snd_uac_chip *uac = prm->uac;
+	struct g_audio *audio_dev = uac->audio_dev;
+	struct uac_params *params = &audio_dev->params;
+
+	if (prm == &uac->c_prm)
+		ucontrol->value.integer.value[0] = params->c_srate;
+	else
+		ucontrol->value.integer.value[0] = params->p_srate;
+
+	return 0;
+}
 
 static struct snd_kcontrol_new u_audio_controls[]  = {
   [UAC_FBACK_CTRL] {
···
 		.info =		u_audio_volume_info,
 		.get =		u_audio_volume_get,
 		.put =		u_audio_volume_put,
+	},
+	[UAC_RATE_CTRL] {
+		.iface =	SNDRV_CTL_ELEM_IFACE_PCM,
+		.name =		"", /* will be filled later */
+		.access =	SNDRV_CTL_ELEM_ACCESS_READ | SNDRV_CTL_ELEM_ACCESS_VOLATILE,
+		.info =		u_audio_rate_info,
+		.get =		u_audio_rate_get,
 	},
 };
 
···
 			prm->volume_min = fu->volume_min;
 			prm->volume_res = fu->volume_res;
 		}
+
+		/* Add rate control */
+		snprintf(ctrl_name, sizeof(ctrl_name),
+				"%s Rate", direction);
+		u_audio_controls[UAC_RATE_CTRL].name = ctrl_name;
+
+		kctl = snd_ctl_new1(&u_audio_controls[UAC_RATE_CTRL], prm);
+		if (!kctl) {
+			err = -ENOMEM;
+			goto snd_fail;
+		}
+
+		kctl->id.device = pcm->device;
+		kctl->id.subdevice = 0;
+
+		err = snd_ctl_add(card, kctl);
+		if (err < 0)
+			goto snd_fail;
+		prm->snd_kctl_rate = kctl;
 	}
 
 	strscpy(card->driver, card_name, sizeof(card->driver));

drivers/usb/gadget/function/u_audio.h

···
 #define __U_AUDIO_H
 
 #include <linux/usb/composite.h>
+#include "uac_common.h"
 
 /*
  * Same maximum frequency deviation on the slower side as in
···
 struct uac_params {
 	/* playback */
 	int p_chmask;	/* channel mask */
-	int p_srate;	/* rate in Hz */
+	int p_srates[UAC_MAX_RATES];	/* available rates in Hz (0 terminated list) */
+	int p_srate;	/* selected 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_srates[UAC_MAX_RATES];	/* available rates in Hz (0 terminated list) */
+	int c_srate;	/* selected rate in Hz */
 	int c_ssize;	/* sample size */
 	struct uac_fu_params c_fu;	/* Feature Unit parameters */
 
···
 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_set_capture_srate(struct g_audio *audio_dev, int srate);
+int u_audio_set_playback_srate(struct g_audio *audio_dev, int srate);
 
 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);

drivers/usb/gadget/function/uac_common.h

···
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ */
+
+#ifndef UAC_COMMON_H
+#define UAC_COMMON_H
+
+#define UAC_MAX_RATES 10 /* maximum number of rates configurable by f_uac1/2 */
+#endif