can: at91_can: at91_poll_err(): increase stats even if no quota left or OOM

at91_poll_err() allocates a can error SKB, to inform the user space
about the CAN error. Then it fills the SKB with information the error
information and increases the net device error stats.

In case no SBK can be allocated (e.g. due to an OOM) or the NAPI quota
is 0 the function is left early and no stats are updated. This is not
helpful to the user, as there is no information about the faulty CAN
bus.

Increase the error stats even if no quota is left or no SKB can be
allocated.

While there treat No-Acknowledgment as a bus error, too.

Link: https://lore.kernel.org/all/20231005-at91_can-rx_offload-v2-18-9987d53600e0@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/at91_can.c

@@ -753,59 +753,64 @@ static int at91_poll_rx(struct net_device *dev, int quota)
 
 static int at91_poll_err(struct net_device *dev, int quota, u32 reg_sr)
 {
+	struct net_device_stats *stats = &dev->stats;
 	struct at91_priv *priv = netdev_priv(dev);
 	struct sk_buff *skb;
-	struct can_frame *cf;
+	struct can_frame *cf = NULL;
 
-	if (quota == 0)
-		return 0;
+	priv->can.can_stats.bus_error++;
 
-	skb = alloc_can_err_skb(dev, &cf);
-	if (unlikely(!skb))
-		return 0;
+	if (quota) {
+		skb = alloc_can_err_skb(dev, &cf);
+		if (cf)
+			cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
+	}
 
-	/* CRC error */
 	if (reg_sr & AT91_IRQ_CERR) {
-		netdev_dbg(dev, "CERR irq\n");
-		dev->stats.rx_errors++;
-		priv->can.can_stats.bus_error++;
-		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
+		netdev_dbg(dev, "CRC error\n");
+
+		stats->rx_errors++;
+		if (cf)
+			cf->data[3] |= CAN_ERR_PROT_LOC_CRC_SEQ;
 	}
 
-	/* Stuffing Error */
 	if (reg_sr & AT91_IRQ_SERR) {
-		netdev_dbg(dev, "SERR irq\n");
-		dev->stats.rx_errors++;
-		priv->can.can_stats.bus_error++;
-		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
-		cf->data[2] |= CAN_ERR_PROT_STUFF;
+		netdev_dbg(dev, "Stuff error\n");
+
+		stats->rx_errors++;
+		if (cf)
+			cf->data[2] |= CAN_ERR_PROT_STUFF;
 	}
 
-	/* Acknowledgement Error */
 	if (reg_sr & AT91_IRQ_AERR) {
-		netdev_dbg(dev, "AERR irq\n");
-		dev->stats.tx_errors++;
-		cf->can_id |= CAN_ERR_ACK;
+		netdev_dbg(dev, "NACK error\n");
+
+		stats->tx_errors++;
+		if (cf) {
+			cf->can_id |= CAN_ERR_ACK;
+			cf->data[2] |= CAN_ERR_PROT_TX;
+		}
 	}
 
-	/* Form error */
 	if (reg_sr & AT91_IRQ_FERR) {
-		netdev_dbg(dev, "FERR irq\n");
-		dev->stats.rx_errors++;
-		priv->can.can_stats.bus_error++;
-		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
-		cf->data[2] |= CAN_ERR_PROT_FORM;
+		netdev_dbg(dev, "Format error\n");
+
+		stats->rx_errors++;
+		if (cf)
+			cf->data[2] |= CAN_ERR_PROT_FORM;
 	}
 
-	/* Bit Error */
 	if (reg_sr & AT91_IRQ_BERR) {
-		netdev_dbg(dev, "BERR irq\n");
-		dev->stats.tx_errors++;
-		priv->can.can_stats.bus_error++;
-		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
-		cf->data[2] |= CAN_ERR_PROT_BIT;
+		netdev_dbg(dev, "Bit error\n");
+
+		stats->tx_errors++;
+		if (cf)
+			cf->data[2] |= CAN_ERR_PROT_TX | CAN_ERR_PROT_BIT;
 	}
 
+	if (!cf)
+		return 0;
+
 	netif_receive_skb(skb);
 
 	return 1;