Bluetooth: btusb: Add support for queuing during polling interval

This makes btusb to queue ACL and events during a polling interval
by using of a delayed work, with the interval working as a time window
where frames received from different endpoints are considered to be
arrived at same time and then attempt to resolve potential conflics by
processing the events ahead of ACL packets.

It worth noting though that priorizing events over ACL data may result
in inverting the order compared to how they appeared over the air, for
instance there may be packets received before a disconnect event that
will be discarded and unencrypted packets received before encryption
change which would considered encrypted, because of these potential
changes on the order the support for queuing during the polling
interval is not enabled by default so it requires setting
force_poll_sync debugfs while the adapter is down.
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/btusb.c

@@ -16,6 +16,7 @@
 #include <linux/of_irq.h>
 #include <linux/suspend.h>
 #include <linux/gpio/consumer.h>
+#include <linux/debugfs.h>
 #include <asm/unaligned.h>
 
 #include <net/bluetooth/bluetooth.h>
@@ -31,7 +32,6 @@
 static bool disable_scofix;
 static bool force_scofix;
 static bool enable_autosuspend = IS_ENABLED(CONFIG_BT_HCIBTUSB_AUTOSUSPEND);
-
 static bool reset = true;
 
 static struct usb_driver btusb_driver;
@@ -561,8 +561,13 @@ struct btusb_data {
 
 	unsigned long flags;
 
-	struct work_struct work;
-	struct work_struct waker;
+	bool poll_sync;
+	int intr_interval;
+	struct work_struct  work;
+	struct work_struct  waker;
+	struct delayed_work rx_work;
+
+	struct sk_buff_head acl_q;
 
 	struct usb_anchor deferred;
 	struct usb_anchor tx_anchor;
@@ -727,6 +732,16 @@ static inline void btusb_free_frags(struct btusb_data *data)
 	spin_unlock_irqrestore(&data->rxlock, flags);
 }
 
+static int btusb_recv_event(struct btusb_data *data, struct sk_buff *skb)
+{
+	if (data->intr_interval) {
+		/* Trigger dequeue immediatelly if an event is received */
+		schedule_delayed_work(&data->rx_work, 0);
+	}
+
+	return data->recv_event(data->hdev, skb);
+}
+
 static int btusb_recv_intr(struct btusb_data *data, void *buffer, int count)
 {
 	struct sk_buff *skb;
@@ -772,7 +787,7 @@ static int btusb_recv_intr(struct btusb_data *data, void *buffer, int count)
 
 		if (!hci_skb_expect(skb)) {
 			/* Complete frame */
-			data->recv_event(data->hdev, skb);
+			btusb_recv_event(data, skb);
 			skb = NULL;
 		}
 	}
@@ -783,6 +798,20 @@ static int btusb_recv_intr(struct btusb_data *data, void *buffer, int count)
 	return err;
 }
 
+static int btusb_recv_acl(struct btusb_data *data, struct sk_buff *skb)
+{
+	/* Only queue ACL packet if intr_interval is set as it means
+	 * force_poll_sync has been enabled.
+	 */
+	if (!data->intr_interval)
+		return data->recv_acl(data->hdev, skb);
+
+	skb_queue_tail(&data->acl_q, skb);
+	schedule_delayed_work(&data->rx_work, data->intr_interval);
+
+	return 0;
+}
+
 static int btusb_recv_bulk(struct btusb_data *data, void *buffer, int count)
 {
 	struct sk_buff *skb;
@@ -830,7 +859,7 @@ static int btusb_recv_bulk(struct btusb_data *data, void *buffer, int count)
 
 		if (!hci_skb_expect(skb)) {
 			/* Complete frame */
-			data->recv_acl(data->hdev, skb);
+			btusb_recv_acl(data, skb);
 			skb = NULL;
 		}
 	}
@@ -986,6 +1015,28 @@ static int btusb_submit_intr_urb(struct hci_dev *hdev, gfp_t mem_flags)
 		usb_unanchor_urb(urb);
 	}
 
+	/* Only initialize intr_interval if URB poll sync is enabled */
+	if (!data->poll_sync)
+		goto done;
+
+	/* The units are frames (milliseconds) for full and low speed devices,
+	 * and microframes (1/8 millisecond) for highspeed and SuperSpeed
+	 * devices.
+	 *
+	 * This is done once on open/resume so it shouldn't change even if
+	 * force_poll_sync changes.
+	 */
+	switch (urb->dev->speed) {
+	case USB_SPEED_SUPER_PLUS:
+	case USB_SPEED_SUPER:	/* units are 125us */
+		data->intr_interval = usecs_to_jiffies(urb->interval * 125);
+		break;
+	default:
+		data->intr_interval = msecs_to_jiffies(urb->interval);
+		break;
+	}
+
+done:
 	usb_free_urb(urb);
 
 	return err;
@@ -1448,9 +1499,12 @@ static int btusb_close(struct hci_dev *hdev)
 
 	BT_DBG("%s", hdev->name);
 
+	cancel_delayed_work(&data->rx_work);
 	cancel_work_sync(&data->work);
 	cancel_work_sync(&data->waker);
 
+	skb_queue_purge(&data->acl_q);
+
 	clear_bit(BTUSB_ISOC_RUNNING, &data->flags);
 	clear_bit(BTUSB_BULK_RUNNING, &data->flags);
 	clear_bit(BTUSB_INTR_RUNNING, &data->flags);
@@ -1482,6 +1536,10 @@ static int btusb_flush(struct hci_dev *hdev)
 
 	BT_DBG("%s", hdev->name);
 
+	cancel_delayed_work(&data->rx_work);
+
+	skb_queue_purge(&data->acl_q);
+
 	usb_kill_anchored_urbs(&data->tx_anchor);
 	btusb_free_frags(data);
 
@@ -1845,6 +1903,17 @@ static void btusb_waker(struct work_struct *work)
 	usb_autopm_put_interface(data->intf);
 }
 
+static void btusb_rx_work(struct work_struct *work)
+{
+	struct btusb_data *data = container_of(work, struct btusb_data,
+					       rx_work.work);
+	struct sk_buff *skb;
+
+	/* Dequeue ACL data received during the interval */
+	while ((skb = skb_dequeue(&data->acl_q)))
+		data->recv_acl(data->hdev, skb);
+}
+
 static int btusb_setup_bcm92035(struct hci_dev *hdev)
 {
 	struct sk_buff *skb;
@@ -3402,6 +3471,49 @@ static int btusb_shutdown_qca(struct hci_dev *hdev)
 	return 0;
 }
 
+static ssize_t force_poll_sync_read(struct file *file, char __user *user_buf,
+				    size_t count, loff_t *ppos)
+{
+	struct btusb_data *data = file->private_data;
+	char buf[3];
+
+	buf[0] = data->poll_sync ? 'Y' : 'N';
+	buf[1] = '\n';
+	buf[2] = '\0';
+	return simple_read_from_buffer(user_buf, count, ppos, buf, 2);
+}
+
+static ssize_t force_poll_sync_write(struct file *file,
+				     const char __user *user_buf,
+				     size_t count, loff_t *ppos)
+{
+	struct btusb_data *data = file->private_data;
+	bool enable;
+	int err;
+
+	err = kstrtobool_from_user(user_buf, count, &enable);
+	if (err)
+		return err;
+
+	/* Only allow changes while the adapter is down */
+	if (test_bit(HCI_UP, &data->hdev->flags))
+		return -EPERM;
+
+	if (data->poll_sync == enable)
+		return -EALREADY;
+
+	data->poll_sync = enable;
+
+	return count;
+}
+
+static const struct file_operations force_poll_sync_fops = {
+	.open		= simple_open,
+	.read		= force_poll_sync_read,
+	.write		= force_poll_sync_write,
+	.llseek		= default_llseek,
+};
+
 static int btusb_probe(struct usb_interface *intf,
 		       const struct usb_device_id *id)
 {
@@ -3485,6 +3597,10 @@ static int btusb_probe(struct usb_interface *intf,
 
 	INIT_WORK(&data->work, btusb_work);
 	INIT_WORK(&data->waker, btusb_waker);
+	INIT_DELAYED_WORK(&data->rx_work, btusb_rx_work);
+
+	skb_queue_head_init(&data->acl_q);
+
 	init_usb_anchor(&data->deferred);
 	init_usb_anchor(&data->tx_anchor);
 	spin_lock_init(&data->txlock);
@@ -3750,6 +3866,9 @@ static int btusb_probe(struct usb_interface *intf,
 
 	usb_set_intfdata(intf, data);
 
+	debugfs_create_file("force_poll_sync", 0644, hdev->debugfs, data,
+			    &force_poll_sync_fops);
+
 	return 0;
 
 out_free_dev: