can: esd_usb: Make use of can_change_state() and relocate checking skb for NULL

Start a rework initiated by Vincents remarks "You should not report
the greatest of txerr and rxerr but the one which actually increased."
[1] and "As far as I understand, those flags should be set only when
the threshold is reached" [2] .

Therefore make use of can_change_state() to (among others) set the
flags CAN_ERR_CRTL_[RT]X_WARNING and CAN_ERR_CRTL_[RT]X_PASSIVE,
maintain CAN statistic counters for error_warning, error_passive and
bus_off.

Relocate testing alloc_can_err_skb() for NULL to the end of
esd_usb_rx_event(), to have things like can_bus_off(),
can_change_state() working even in out of memory conditions.

Fixes: 96d8e903 ("can: Add driver for esd CAN-USB/2 device")
Signed-off-by: Frank Jungclaus <frank.jungclaus@esd.eu>
Link: [1] https://lore.kernel.org/all/CAMZ6RqKGBWe15aMkf8-QLf-cOQg99GQBebSm+1wEzTqHgvmNuw@mail.gmail.com/
Link: [2] https://lore.kernel.org/all/CAMZ6Rq+QBO1yTX_o6GV0yhdBj-RzZSRGWDZBS0fs7zbSTy4hmA@mail.gmail.com/
Link: https://lore.kernel.org/all/20230216190450.3901254-3-frank.jungclaus@esd.euSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/esd_usb.c

@@ -239,41 +239,42 @@ static void esd_usb_rx_event(struct esd_usb_net_priv *priv,
 			   msg->msg.rx.dlc, state, ecc, rxerr, txerr);
 
 		skb = alloc_can_err_skb(priv->netdev, &cf);
-		if (skb == NULL) {
-			stats->rx_dropped++;
-			return;
-		}
 
 		if (state != priv->old_state) {
+			enum can_state tx_state, rx_state;
+			enum can_state new_state = CAN_STATE_ERROR_ACTIVE;
+
 			priv->old_state = state;
 
 			switch (state & ESD_BUSSTATE_MASK) {
 			case ESD_BUSSTATE_BUSOFF:
-				priv->can.state = CAN_STATE_BUS_OFF;
-				cf->can_id |= CAN_ERR_BUSOFF;
-				priv->can.can_stats.bus_off++;
+				new_state = CAN_STATE_BUS_OFF;
 				can_bus_off(priv->netdev);
 				break;
 			case ESD_BUSSTATE_WARN:
-				priv->can.state = CAN_STATE_ERROR_WARNING;
-				priv->can.can_stats.error_warning++;
+				new_state = CAN_STATE_ERROR_WARNING;
 				break;
 			case ESD_BUSSTATE_ERRPASSIVE:
-				priv->can.state = CAN_STATE_ERROR_PASSIVE;
-				priv->can.can_stats.error_passive++;
+				new_state = CAN_STATE_ERROR_PASSIVE;
 				break;
 			default:
-				priv->can.state = CAN_STATE_ERROR_ACTIVE;
+				new_state = CAN_STATE_ERROR_ACTIVE;
 				txerr = 0;
 				rxerr = 0;
 				break;
 			}
-		} else {
+
+			if (new_state != priv->can.state) {
+				tx_state = (txerr >= rxerr) ? new_state : 0;
+				rx_state = (txerr <= rxerr) ? new_state : 0;
+				can_change_state(priv->netdev, cf,
+						 tx_state, rx_state);
+			}
+		} else if (skb) {
 			priv->can.can_stats.bus_error++;
 			stats->rx_errors++;
 
-			cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR |
-				      CAN_ERR_CNT;
+			cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
 
 			switch (ecc & SJA1000_ECC_MASK) {
 			case SJA1000_ECC_BIT:
@@ -295,21 +296,20 @@ static void esd_usb_rx_event(struct esd_usb_net_priv *priv,
 
 			/* Bit stream position in CAN frame as the error was detected */
 			cf->data[3] = ecc & SJA1000_ECC_SEG;
-
-			if (priv->can.state == CAN_STATE_ERROR_WARNING ||
-			    priv->can.state == CAN_STATE_ERROR_PASSIVE) {
-				cf->data[1] = (txerr > rxerr) ?
-					CAN_ERR_CRTL_TX_PASSIVE :
-					CAN_ERR_CRTL_RX_PASSIVE;
-			}
-			cf->data[6] = txerr;
-			cf->data[7] = rxerr;
 		}
 
 		priv->bec.txerr = txerr;
 		priv->bec.rxerr = rxerr;
 
-		netif_rx(skb);
+		if (skb) {
+			cf->can_id |= CAN_ERR_CNT;
+			cf->data[6] = txerr;
+			cf->data[7] = rxerr;
+
+			netif_rx(skb);
+		} else {
+			stats->rx_dropped++;
+		}
 	}
 }