can: gs_usb: add support for reading error counters

Add support for reading the device state and CAN error counters, using
the GS_USB_BREQ_GET_STATE control message, if supported by the device,
indicated by the GS_CAN_FEATURE_GET_STATE feature flag.
Signed-off-by: Jeroen Hofstee <jhofstee@victronenergy.com>
Link: https://lore.kernel.org/all/20221019221016.1659260-8-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -961,6 +961,42 @@ static int gs_can_open(struct net_device *netdev)
 	return 0;
 }
 
+static int gs_usb_get_state(const struct net_device *netdev,
+			    struct can_berr_counter *bec,
+			    enum can_state *state)
+{
+	struct gs_can *dev = netdev_priv(netdev);
+	struct gs_device_state ds;
+	int rc;
+
+	rc = usb_control_msg_recv(interface_to_usbdev(dev->iface), 0,
+				  GS_USB_BREQ_GET_STATE,
+				  USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_INTERFACE,
+				  dev->channel, 0,
+				  &ds, sizeof(ds),
+				  USB_CTRL_GET_TIMEOUT,
+				  GFP_KERNEL);
+	if (rc)
+		return rc;
+
+	if (le32_to_cpu(ds.state) >= CAN_STATE_MAX)
+		return -EOPNOTSUPP;
+
+	*state = le32_to_cpu(ds.state);
+	bec->txerr = le32_to_cpu(ds.txerr);
+	bec->rxerr = le32_to_cpu(ds.rxerr);
+
+	return 0;
+}
+
+static int gs_usb_can_get_berr_counter(const struct net_device *netdev,
+				       struct can_berr_counter *bec)
+{
+	enum can_state state;
+
+	return gs_usb_get_state(netdev, bec, &state);
+}
+
 static int gs_can_close(struct net_device *netdev)
 {
 	int rc;
@@ -1235,6 +1271,9 @@ static struct gs_can *gs_make_candev(unsigned int channel,
 	if (feature & GS_CAN_FEATURE_BERR_REPORTING)
 		dev->can.ctrlmode_supported |= CAN_CTRLMODE_BERR_REPORTING;
 
+	if (feature & GS_CAN_FEATURE_GET_STATE)
+		dev->can.do_get_berr_counter = gs_usb_can_get_berr_counter;
+
 	/* The CANtact Pro from LinkLayer Labs is based on the
 	 * LPC54616 µC, which is affected by the NXP LPC USB transfer
 	 * erratum. However, the current firmware (version 2) doesn't