can: esd_usb: Allow REC and TEC to return to zero

[ Upstream commit 918ee49 ]

We don't get any further EVENT from an esd CAN USB device for changes
on REC or TEC while those counters converge to 0 (with ecc == 0). So
when handling the "Back to Error Active"-event force txerr = rxerr =
0, otherwise the berr-counters might stay on values like 95 forever.

Also, to make life easier during the ongoing development a
netdev_dbg() has been introduced to allow dumping error events send by
an esd CAN USB device.

Fixes: 96d8e90 ("can: Add driver for esd CAN-USB/2 device")
Signed-off-by: Frank Jungclaus <frank.jungclaus@esd.eu>
Link: https://lore.kernel.org/all/20221130202242.3998219-2-frank.jungclaus@esd.eu
Cc: stable@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/can/usb/esd_usb2.c

@@ -227,6 +227,10 @@ static void esd_usb2_rx_event(struct esd_usb2_net_priv *priv,
 		u8 rxerr = msg->msg.rx.data[2];
 		u8 txerr = msg->msg.rx.data[3];
 
+		netdev_dbg(priv->netdev,
+			   "CAN_ERR_EV_EXT: dlc=%#02x state=%02x ecc=%02x rec=%02x tec=%02x\n",
+			   msg->msg.rx.dlc, state, ecc, rxerr, txerr);
+
 		skb = alloc_can_err_skb(priv->netdev, &cf);
 		if (skb == NULL) {
 			stats->rx_dropped++;
@@ -253,6 +257,8 @@ static void esd_usb2_rx_event(struct esd_usb2_net_priv *priv,
 				break;
 			default:
 				priv->can.state = CAN_STATE_ERROR_ACTIVE;
+				txerr = 0;
+				rxerr = 0;
 				break;
 			}
 		} else {