Bluetooth: btusb: handle mSBC audio over USB Endpoints

For mSBC encoded audio stream over usb transport, btusb driver
to be set to alternate settings 6 as per BT core spec 5.0. The
type of air mode is used to differenting which alt setting to be
used.

The changes are made considering some discussion over the similar
patch submitted earlier from Kuba Pawlak (link below)
https://www.spinics.net/lists/linux-bluetooth/msg64577.html

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Sathish Narasimman <sathish.narasimman@intel.com>
Signed-off-by: Chethan T N <chethan.tumkur.narayan@intel.com>
Signed-off-by: Hsin-Yu Chao <hychao@chromium.org>
Signed-off-by: Amit K Bag <amit.k.bag@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

drivers/bluetooth/btusb.c

@@ -492,6 +492,8 @@ struct btusb_data {
 	__u8 cmdreq;
 
 	unsigned int sco_num;
+	unsigned int air_mode;
+	bool usb_alt6_packet_flow;
 	int isoc_altsetting;
 	int suspend_count;
 
@@ -983,6 +985,42 @@ static void btusb_isoc_complete(struct urb *urb)
 	}
 }
 
+static inline void __fill_isoc_descriptor_msbc(struct urb *urb, int len,
+					       int mtu, struct btusb_data *data)
+{
+	int i, offset = 0;
+	unsigned int interval;
+
+	BT_DBG("len %d mtu %d", len, mtu);
+
+	/* For mSBC ALT 6 setting the host will send the packet at continuous
+	 * flow. As per core spec 5, vol 4, part B, table 2.1. For ALT setting
+	 * 6 the HCI PACKET INTERVAL should be 7.5ms for every usb packets.
+	 * To maintain the rate we send 63bytes of usb packets alternatively for
+	 * 7ms and 8ms to maintain the rate as 7.5ms.
+	 */
+	if (data->usb_alt6_packet_flow) {
+		interval = 7;
+		data->usb_alt6_packet_flow = false;
+	} else {
+		interval = 6;
+		data->usb_alt6_packet_flow = true;
+	}
+
+	for (i = 0; i < interval; i++) {
+		urb->iso_frame_desc[i].offset = offset;
+		urb->iso_frame_desc[i].length = offset;
+	}
+
+	if (len && i < BTUSB_MAX_ISOC_FRAMES) {
+		urb->iso_frame_desc[i].offset = offset;
+		urb->iso_frame_desc[i].length = len;
+		i++;
+	}
+
+	urb->number_of_packets = i;
+}
+
 static inline void __fill_isoc_descriptor(struct urb *urb, int len, int mtu)
 {
 	int i, offset = 0;
@@ -1386,9 +1424,13 @@ static struct urb *alloc_isoc_urb(struct hci_dev *hdev, struct sk_buff *skb)
 
 	urb->transfer_flags  = URB_ISO_ASAP;
 
-	__fill_isoc_descriptor(urb, skb->len,
+	if (data->isoc_altsetting == 6)
-			       le16_to_cpu(data->isoc_tx_ep->wMaxPacketSize));
+		__fill_isoc_descriptor_msbc(urb, skb->len,
-
+					    le16_to_cpu(data->isoc_tx_ep->wMaxPacketSize),
+					    data);
+	else
+		__fill_isoc_descriptor(urb, skb->len,
+				       le16_to_cpu(data->isoc_tx_ep->wMaxPacketSize));
 	skb->dev = (void *)hdev;
 
 	return urb;
@@ -1484,6 +1526,7 @@ static void btusb_notify(struct hci_dev *hdev, unsigned int evt)
 
 	if (hci_conn_num(hdev, SCO_LINK) != data->sco_num) {
 		data->sco_num = hci_conn_num(hdev, SCO_LINK);
+		data->air_mode = evt;
 		schedule_work(&data->work);
 	}
 }
@@ -1531,11 +1574,67 @@ static inline int __set_isoc_interface(struct hci_dev *hdev, int altsetting)
 	return 0;
 }
 
+static int btusb_switch_alt_setting(struct hci_dev *hdev, int new_alts)
+{
+	struct btusb_data *data = hci_get_drvdata(hdev);
+	int err;
+
+	if (data->isoc_altsetting != new_alts) {
+		unsigned long flags;
+
+		clear_bit(BTUSB_ISOC_RUNNING, &data->flags);
+		usb_kill_anchored_urbs(&data->isoc_anchor);
+
+		/* When isochronous alternate setting needs to be
+		 * changed, because SCO connection has been added
+		 * or removed, a packet fragment may be left in the
+		 * reassembling state. This could lead to wrongly
+		 * assembled fragments.
+		 *
+		 * Clear outstanding fragment when selecting a new
+		 * alternate setting.
+		 */
+		spin_lock_irqsave(&data->rxlock, flags);
+		kfree_skb(data->sco_skb);
+		data->sco_skb = NULL;
+		spin_unlock_irqrestore(&data->rxlock, flags);
+
+		err = __set_isoc_interface(hdev, new_alts);
+		if (err < 0)
+			return err;
+	}
+
+	if (!test_and_set_bit(BTUSB_ISOC_RUNNING, &data->flags)) {
+		if (btusb_submit_isoc_urb(hdev, GFP_KERNEL) < 0)
+			clear_bit(BTUSB_ISOC_RUNNING, &data->flags);
+		else
+			btusb_submit_isoc_urb(hdev, GFP_KERNEL);
+	}
+
+	return 0;
+}
+
+static struct usb_host_interface *btusb_find_altsetting(struct btusb_data *data,
+							int alt)
+{
+	struct usb_interface *intf = data->isoc;
+	int i;
+
+	BT_DBG("Looking for Alt no :%d", alt);
+
+	for (i = 0; i < intf->num_altsetting; i++) {
+		if (intf->altsetting[i].desc.bAlternateSetting == alt)
+			return &intf->altsetting[i];
+	}
+
+	return NULL;
+}
+
 static void btusb_work(struct work_struct *work)
 {
 	struct btusb_data *data = container_of(work, struct btusb_data, work);
 	struct hci_dev *hdev = data->hdev;
-	int new_alts;
+	int new_alts = 0;
 	int err;
 
 	if (data->sco_num > 0) {
@@ -1550,44 +1649,27 @@ static void btusb_work(struct work_struct *work)
 			set_bit(BTUSB_DID_ISO_RESUME, &data->flags);
 		}
 
-		if (hdev->voice_setting & 0x0020) {
+		if (data->air_mode == HCI_NOTIFY_ENABLE_SCO_CVSD) {
-			static const int alts[3] = { 2, 4, 5 };
+			if (hdev->voice_setting & 0x0020) {
+				static const int alts[3] = { 2, 4, 5 };
 
-			new_alts = alts[data->sco_num - 1];
+				new_alts = alts[data->sco_num - 1];
-		} else {
+			} else {
-			new_alts = data->sco_num;
+				new_alts = data->sco_num;
-		}
+			}
+		} else if (data->air_mode == HCI_NOTIFY_ENABLE_SCO_TRANSP) {
 
-		if (data->isoc_altsetting != new_alts) {
+			data->usb_alt6_packet_flow = true;
-			unsigned long flags;
 
-			clear_bit(BTUSB_ISOC_RUNNING, &data->flags);
+			/* Check if Alt 6 is supported for Transparent audio */
-			usb_kill_anchored_urbs(&data->isoc_anchor);
+			if (btusb_find_altsetting(data, 6))
-
+				new_alts = 6;
-			/* When isochronous alternate setting needs to be
-			 * changed, because SCO connection has been added
-			 * or removed, a packet fragment may be left in the
-			 * reassembling state. This could lead to wrongly
-			 * assembled fragments.
-			 *
-			 * Clear outstanding fragment when selecting a new
-			 * alternate setting.
-			 */
-			spin_lock_irqsave(&data->rxlock, flags);
-			kfree_skb(data->sco_skb);
-			data->sco_skb = NULL;
-			spin_unlock_irqrestore(&data->rxlock, flags);
-
-			if (__set_isoc_interface(hdev, new_alts) < 0)
-				return;
-		}
-
-		if (!test_and_set_bit(BTUSB_ISOC_RUNNING, &data->flags)) {
-			if (btusb_submit_isoc_urb(hdev, GFP_KERNEL) < 0)
-				clear_bit(BTUSB_ISOC_RUNNING, &data->flags);
 			else
-				btusb_submit_isoc_urb(hdev, GFP_KERNEL);
+				bt_dev_err(hdev, "Device does not support ALT setting 6");
 		}
+
+		if (btusb_switch_alt_setting(hdev, new_alts) < 0)
+			bt_dev_err(hdev, "set USB alt:(%d) failed!", new_alts);
 	} else {
 		clear_bit(BTUSB_ISOC_RUNNING, &data->flags);
 		usb_kill_anchored_urbs(&data->isoc_anchor);