+static int
+snd_usb_offload_route_get(struct snd_kcontrol *kcontrol,
+			  struct snd_ctl_elem_value *ucontrol)
+{
+	struct device *sysdev = snd_kcontrol_chip(kcontrol);
+	int ret;
+
+	ret = snd_soc_usb_update_offload_route(sysdev,
+					       CARD_IDX(kcontrol->private_value),
+					       PCM_IDX(kcontrol->private_value),
+					       SNDRV_PCM_STREAM_PLAYBACK,
+					       ucontrol->value.integer.value);
+	if (ret < 0) {
+		ucontrol->value.integer.value[0] = -1;
+		ucontrol->value.integer.value[1] = -1;
+	}

well this invalidates again what I understood from the last patch and
goes back to what I understood initially: the error code is never
returned to higher levels - when offload is not supported the kcontrol
values are encoded to the -1 magic value.

+	return 0;

and this begs the question if this helper should return a void value.

+}
+
+static int snd_usb_offload_route_info(struct snd_kcontrol *kcontrol,
+				      struct snd_ctl_elem_info *uinfo)
+{
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = 2;
+	uinfo->value.integer.min = -1;
+	/* Arbitrary max value, as there is no 'limit' on number of PCM devices */
+	uinfo->value.integer.max = 0xff;
+
+	return 0;
+}
+
+static struct snd_kcontrol_new snd_usb_offload_mapped_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_CARD,
+	.access = SNDRV_CTL_ELEM_ACCESS_READ,
+	.info = snd_usb_offload_route_info,
+	.get = snd_usb_offload_route_get,
+};
+
+/**
+ * snd_usb_offload_create_ctl() - Add USB offload bounded mixer
+ * @chip - USB SND chip device
+ *
+ * Creates a sound control for a USB audio device, so that applications can
+ * query for if there is an available USB audio offload path, and which
+ * card is managing it.
+ */
+int snd_usb_offload_create_ctl(struct snd_usb_audio *chip)
+{
+	struct usb_device *udev = chip->dev;
+	struct snd_kcontrol_new *chip_kctl;
+	struct snd_usb_substream *subs;
+	struct snd_usb_stream *as;
+	char ctl_name[37];

that's quite a magic value.

+	int ret;
+
+	list_for_each_entry(as, &chip->pcm_list, list) {
+		subs = &as->substream[SNDRV_PCM_STREAM_PLAYBACK];
+		if (!subs->ep_num)
+			continue;
+
+		chip_kctl = &snd_usb_offload_mapped_ctl;
+		chip_kctl->count = 1;
+		/*
+		 * Store the associated USB SND card number and PCM index for
+		 * the kctl.
+		 */
+		chip_kctl->private_value = as->pcm_index |
+					  chip->card->number << 16;
+		sprintf(ctl_name, "USB Offload Playback Route PCM#%d",
+			as->pcm_index);
+		chip_kctl->name = ctl_name;
+		ret = snd_ctl_add(chip->card, snd_ctl_new1(chip_kctl,
+				  udev->bus->sysdev));
+		if (ret < 0)
+			break;
+	}
+
+	return ret;
+}