Bluetooth: hci_h5: implement CRC data integrity

The UART-based H5 protocol supports CRC data integrity checks for
reliable packets. The host sets bit 5 in the configuration field of the
CONFIG link control message to indicate that CRC is supported. The
controller sets the same bit in the CONFIG RESPONSE message to indicate
that CRC may be used from then on.

Tested on a MangoPi MQ-Pro with a Realtek RTL8723DS Bluetooth controller
using the tip of the bluetooth-next tree.

Signed-off-by: Javier Nieto <[e-mail]>
Signed-off-by: Luiz Augusto von Dentz <[e-mail]>

drivers/bluetooth/Kconfig

···
 	bool "Three-wire UART (H5) protocol support"
 	depends on BT_HCIUART
 	depends on BT_HCIUART_SERDEV
+	select CRC_CCITT
 	help
 	  The HCI Three-wire UART Transport Layer makes it possible to
 	  user the Bluetooth HCI over a serial port interface. The HCI

drivers/bluetooth/hci_h5.c

···
  */
 
 #include <linux/acpi.h>
+#include <linux/bitrev.h>
+#include <linux/crc-ccitt.h>
 #include <linux/errno.h>
 #include <linux/gpio/consumer.h>
 #include <linux/kernel.h>
···
 	H5_TX_ACK_REQ,		/* Pending ack to send */
 	H5_WAKEUP_DISABLE,	/* Device cannot wake host */
 	H5_HW_FLOW_CONTROL,	/* Use HW flow control */
+	H5_CRC,			/* Use CRC */
 };
 
 struct h5 {
···
 
 static u8 h5_cfg_field(struct h5 *h5)
 {
-	/* Sliding window size (first 3 bits) */
-	return h5->tx_win & 0x07;
+	/* Sliding window size (first 3 bits) and CRC request (fifth bit). */
+	return (h5->tx_win & 0x07) | 0x10;
 }
 
 static void h5_timed_event(struct timer_list *t)
···
 		h5_link_control(hu, conf_rsp, 2);
 		h5_link_control(hu, conf_req, 3);
 	} else if (memcmp(data, conf_rsp, 2) == 0) {
-		if (H5_HDR_LEN(hdr) > 2)
+		if (H5_HDR_LEN(hdr) > 2) {
 			h5->tx_win = (data[2] & 0x07);
+			assign_bit(H5_CRC, &h5->flags, data[2] & 0x10);
+		}
 		BT_DBG("Three-wire init complete. tx_win %u", h5->tx_win);
 		h5->state = H5_ACTIVE;
 		hci_uart_init_ready(hu);
···
 
 static int h5_rx_crc(struct hci_uart *hu, unsigned char c)
 {
-	h5_complete_rx_pkt(hu);
+	struct h5 *h5 = hu->priv;
+	const unsigned char *hdr = h5->rx_skb->data;
+	u16 crc;
+	__be16 crc_be;
+
+	crc = crc_ccitt(0xffff, hdr, 4 + H5_HDR_LEN(hdr));
+	crc = bitrev16(crc);
+
+	crc_be = cpu_to_be16(crc);
+
+	if (memcmp(&crc_be, hdr + 4 + H5_HDR_LEN(hdr), 2) != 0) {
+		bt_dev_err(hu->hdev, "Received packet with invalid CRC");
+		h5_reset_rx(h5);
+	} else {
+		/* Remove CRC bytes */
+		skb_trim(h5->rx_skb, 4 + H5_HDR_LEN(hdr));
+		h5_complete_rx_pkt(hu);
+	}
 
 	return 0;
 }
···
 	h5->rx_func = h5_rx_delimiter;
 	h5->rx_pending = 0;
 	clear_bit(H5_RX_ESC, &h5->flags);
+	clear_bit(H5_CRC, &h5->flags);
 }
 
 static int h5_recv(struct hci_uart *hu, const void *data, int count)
···
 	struct h5 *h5 = hu->priv;
 	struct sk_buff *nskb;
 	u8 hdr[4];
+	u16 crc;
 	int i;
 
 	if (!valid_packet_type(pkt_type)) {
···
 	/* Reliable packet? */
 	if (pkt_type == HCI_ACLDATA_PKT || pkt_type == HCI_COMMAND_PKT) {
 		hdr[0] |= 1 << 7;
+		hdr[0] |= (test_bit(H5_CRC, &h5->flags) && 1) << 6;
 		hdr[0] |= h5->tx_seq;
 		h5->tx_seq = (h5->tx_seq + 1) % 8;
 	}
···
 
 	for (i = 0; i < len; i++)
 		h5_slip_one_byte(nskb, data[i]);
+
+	if (H5_HDR_CRC(hdr)) {
+		crc = crc_ccitt(0xffff, hdr, 4);
+		crc = crc_ccitt(crc, data, len);
+		crc = bitrev16(crc);
+
+		h5_slip_one_byte(nskb, (crc >> 8) & 0xff);
+		h5_slip_one_byte(nskb, crc & 0xff);
+	}
 
 	h5_slip_delim(nskb);