Bluetooth: btusb: add sysfs attribute to control USB alt setting

When a Bluetooth raw socket is open, the HCI event related to SCO
connection changes are not dispatched to the hci_event module, and
the underlying Bluetooth controller's USB Interface 1 will not be
updated accordingly.

This patch adds `isoc_alt` sysfs attribute, allowing user space
to update the alternate setting of the USB interface alternate
setting as needed.

Signed-off-by: Ying Hsu <[email protected]>
Signed-off-by: Luiz Augusto von Dentz <[email protected]>

drivers/bluetooth/btusb.c

@@ -3647,6 +3647,32 @@ static const struct file_operations force_poll_sync_fops = {
 	.llseek		= default_llseek,
 };
 
+static ssize_t isoc_alt_show(struct device *dev,
+			     struct device_attribute *attr,
+			     char *buf)
+{
+	struct btusb_data *data = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%d\n", data->isoc_altsetting);
+}
+
+static ssize_t isoc_alt_store(struct device *dev,
+			      struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct btusb_data *data = dev_get_drvdata(dev);
+	int alt;
+	int ret;
+
+	if (kstrtoint(buf, 10, &alt))
+		return -EINVAL;
+
+	ret = btusb_switch_alt_setting(data->hdev, alt);
+	return ret < 0 ? ret : count;
+}
+
+static DEVICE_ATTR_RW(isoc_alt);
+
 static int btusb_probe(struct usb_interface *intf,
 		       const struct usb_device_id *id)
 {
@@ -4010,6 +4036,10 @@ static int btusb_probe(struct usb_interface *intf,
 						 data->isoc, data);
 		if (err < 0)
 			goto out_free_dev;
+
+		err = device_create_file(&intf->dev, &dev_attr_isoc_alt);
+		if (err)
+			goto out_free_dev;
 	}
 
 	if (IS_ENABLED(CONFIG_BT_HCIBTUSB_BCM) && data->diag) {
@@ -4056,8 +4086,10 @@ static void btusb_disconnect(struct usb_interface *intf)
 	hdev = data->hdev;
 	usb_set_intfdata(data->intf, NULL);
 
-	if (data->isoc)
+	if (data->isoc) {
+		device_remove_file(&intf->dev, &dev_attr_isoc_alt);
 		usb_set_intfdata(data->isoc, NULL);
+	}
 
 	if (data->diag)
 		usb_set_intfdata(data->diag, NULL);