Bluetooth: Introduce HCI Driver protocol

Although commit 75ddcd5ad40e ("Bluetooth: btusb: Configure altsetting
for HCI_USER_CHANNEL") has enabled the HCI_USER_CHANNEL user to send out
SCO data through USB Bluetooth chips, it's observed that with the patch
HFP is flaky on most of the existing USB Bluetooth controllers: Intel
chips sometimes send out no packet for Transparent codec; MTK chips may
generate SCO data with a wrong handle for CVSD codec; RTK could split
the data with a wrong packet size for Transparent codec; ... etc.

To address the issue above one needs to reset the altsetting back to
zero when there is no active SCO connection, which is the same as the
BlueZ behavior, and another benefit is the bus doesn't need to reserve
bandwidth when no SCO connection.

This patch adds the infrastructure that allow the user space program to
talk to Bluetooth drivers directly:
- Define the new packet type HCI_DRV_PKT which is specifically used for
  communication between the user space program and the Bluetooth drviers
- hci_send_frame intercepts the packets and invokes drivers' HCI Drv
  callbacks (so far only defined for btusb)
- 2 kinds of events to user space: Command Status and Command Complete,
  the former simply returns the status while the later may contain
  additional response data.

Cc: chromeos-bluetooth-upstreaming@chromium.org
Fixes: b16b327edb4d ("Bluetooth: btusb: add sysfs attribute to control USB alt setting")
Signed-off-by: Hsin-chen Chuang <chharry@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

4 files changed, 128 insertions, 3 deletions

diff --git a/net/bluetooth/Makefile b/net/bluetooth/Makefile
index 5a3835b7dfcd..a7eede7616d8 100644
--- a/net/bluetooth/Makefile
+++ b/net/bluetooth/Makefile
@@ -14,7 +14,8 @@ bluetooth_6lowpan-y := 6lowpan.o
 
 bluetooth-y := af_bluetooth.o hci_core.o hci_conn.o hci_event.o mgmt.o \
 	hci_sock.o hci_sysfs.o l2cap_core.o l2cap_sock.o smp.o lib.o \
-	ecdh_helper.o mgmt_util.o mgmt_config.o hci_codec.o eir.o hci_sync.o
+	ecdh_helper.o mgmt_util.o mgmt_config.o hci_codec.o eir.o hci_sync.o \
+	hci_drv.o
 
 bluetooth-$(CONFIG_DEV_COREDUMP) += coredump.o
 
diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 5eb0600bbd03..df7d7bf32eb8 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -2911,6 +2911,8 @@ int hci_recv_frame(struct hci_dev *hdev, struct sk_buff *skb)
 		break;
 	case HCI_ISODATA_PKT:
 		break;
+	case HCI_DRV_PKT:
+		break;
 	default:
 		kfree_skb(skb);
 		return -EINVAL;
@@ -3019,6 +3021,15 @@ static int hci_send_frame(struct hci_dev *hdev, struct sk_buff *skb)
 		return -EINVAL;
 	}
 
+	if (hci_skb_pkt_type(skb) == HCI_DRV_PKT) {
+		/* Intercept HCI Drv packet here and don't go with hdev->send
+		 * callback.
+		 */
+		err = hci_drv_process_cmd(hdev, skb);
+		kfree_skb(skb);
+		return err;
+	}
+
 	err = hdev->send(hdev, skb);
 	if (err < 0) {
 		bt_dev_err(hdev, "sending frame failed (%d)", err);
diff --git a/net/bluetooth/hci_drv.c b/net/bluetooth/hci_drv.c
new file mode 100644
index 000000000000..3dd2d8a006b9
--- /dev/null
+++ b/net/bluetooth/hci_drv.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Google Corporation
+ */
+
+#include <linux/skbuff.h>
+#include <linux/types.h>
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci.h>
+#include <net/bluetooth/hci_core.h>
+#include <net/bluetooth/hci_drv.h>
+
+int hci_drv_cmd_status(struct hci_dev *hdev, u16 cmd, u8 status)
+{
+	struct hci_drv_ev_hdr *hdr;
+	struct hci_drv_ev_cmd_status *ev;
+	struct sk_buff *skb;
+
+	skb = bt_skb_alloc(sizeof(*hdr) + sizeof(*ev), GFP_KERNEL);
+	if (!skb)
+		return -ENOMEM;
+
+	hdr = skb_put(skb, sizeof(*hdr));
+	hdr->opcode = __cpu_to_le16(HCI_DRV_EV_CMD_STATUS);
+	hdr->len = __cpu_to_le16(sizeof(*ev));
+
+	ev = skb_put(skb, sizeof(*ev));
+	ev->opcode = __cpu_to_le16(cmd);
+	ev->status = status;
+
+	hci_skb_pkt_type(skb) = HCI_DRV_PKT;
+
+	return hci_recv_frame(hdev, skb);
+}
+EXPORT_SYMBOL(hci_drv_cmd_status);
+
+int hci_drv_cmd_complete(struct hci_dev *hdev, u16 cmd, u8 status, void *rp,
+			 size_t rp_len)
+{
+	struct hci_drv_ev_hdr *hdr;
+	struct hci_drv_ev_cmd_complete *ev;
+	struct sk_buff *skb;
+
+	skb = bt_skb_alloc(sizeof(*hdr) + sizeof(*ev) + rp_len, GFP_KERNEL);
+	if (!skb)
+		return -ENOMEM;
+
+	hdr = skb_put(skb, sizeof(*hdr));
+	hdr->opcode = __cpu_to_le16(HCI_DRV_EV_CMD_COMPLETE);
+	hdr->len = __cpu_to_le16(sizeof(*ev) + rp_len);
+
+	ev = skb_put(skb, sizeof(*ev));
+	ev->opcode = __cpu_to_le16(cmd);
+	ev->status = status;
+
+	skb_put_data(skb, rp, rp_len);
+
+	hci_skb_pkt_type(skb) = HCI_DRV_PKT;
+
+	return hci_recv_frame(hdev, skb);
+}
+EXPORT_SYMBOL(hci_drv_cmd_complete);
+
+int hci_drv_process_cmd(struct hci_dev *hdev, struct sk_buff *skb)
+{
+	struct hci_drv_cmd_hdr *hdr;
+	const struct hci_drv_handler *handler = NULL;
+	u16 opcode, len, ogf, ocf;
+
+	hdr = skb_pull_data(skb, sizeof(*hdr));
+	if (!hdr)
+		return -EILSEQ;
+
+	opcode = __le16_to_cpu(hdr->opcode);
+	len = __le16_to_cpu(hdr->len);
+	if (len != skb->len)
+		return -EILSEQ;
+
+	ogf = hci_opcode_ogf(opcode);
+	ocf = hci_opcode_ocf(opcode);
+
+	if (!hdev->hci_drv)
+		return hci_drv_cmd_status(hdev, opcode,
+					  HCI_DRV_STATUS_UNKNOWN_COMMAND);
+
+	if (ogf != HCI_DRV_OGF_DRIVER_SPECIFIC) {
+		if (opcode < hdev->hci_drv->common_handler_count)
+			handler = &hdev->hci_drv->common_handlers[opcode];
+	} else {
+		if (ocf < hdev->hci_drv->specific_handler_count)
+			handler = &hdev->hci_drv->specific_handlers[ocf];
+	}
+
+	if (!handler || !handler->func)
+		return hci_drv_cmd_status(hdev, opcode,
+					  HCI_DRV_STATUS_UNKNOWN_COMMAND);
+
+	if (len != handler->data_len)
+		return hci_drv_cmd_status(hdev, opcode,
+					  HCI_DRV_STATUS_INVALID_PARAMETERS);
+
+	return handler->func(hdev, skb->data, len);
+}
+EXPORT_SYMBOL(hci_drv_process_cmd);
diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index 022b86797acd..428ee5c7de7e 100644
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -234,7 +234,8 @@ void hci_send_to_sock(struct hci_dev *hdev, struct sk_buff *skb)
 			if (hci_skb_pkt_type(skb) != HCI_EVENT_PKT &&
 			    hci_skb_pkt_type(skb) != HCI_ACLDATA_PKT &&
 			    hci_skb_pkt_type(skb) != HCI_SCODATA_PKT &&
-			    hci_skb_pkt_type(skb) != HCI_ISODATA_PKT)
+			    hci_skb_pkt_type(skb) != HCI_ISODATA_PKT &&
+			    hci_skb_pkt_type(skb) != HCI_DRV_PKT)
 				continue;
 		} else {
 			/* Don't send frame to other channel types */
@@ -391,6 +392,12 @@ void hci_send_to_monitor(struct hci_dev *hdev, struct sk_buff *skb)
 		else
 			opcode = cpu_to_le16(HCI_MON_ISO_TX_PKT);
 		break;
+	case HCI_DRV_PKT:
+		if (bt_cb(skb)->incoming)
+			opcode = cpu_to_le16(HCI_MON_DRV_RX_PKT);
+		else
+			opcode = cpu_to_le16(HCI_MON_DRV_TX_PKT);
+		break;
 	case HCI_DIAG_PKT:
 		opcode = cpu_to_le16(HCI_MON_VENDOR_DIAG);
 		break;
@@ -1860,7 +1867,8 @@ static int hci_sock_sendmsg(struct socket *sock, struct msghdr *msg,
 		if (hci_skb_pkt_type(skb) != HCI_COMMAND_PKT &&
 		    hci_skb_pkt_type(skb) != HCI_ACLDATA_PKT &&
 		    hci_skb_pkt_type(skb) != HCI_SCODATA_PKT &&
-		    hci_skb_pkt_type(skb) != HCI_ISODATA_PKT) {
+		    hci_skb_pkt_type(skb) != HCI_ISODATA_PKT &&
+		    hci_skb_pkt_type(skb) != HCI_DRV_PKT) {
 			err = -EINVAL;
 			goto drop;
 		}