Re: [PATCH v3 2/3] net: ethernet: actions: Add Actions Semi Owl Ethernet MAC driver

On Tue, Mar 23, 2021 at 12:38:10AM +0100, Andrew Lunn wrote:

quoted

+static void owl_emac_set_multicast(struct net_device *netdev, int count)
+{
+	struct owl_emac_priv *priv = netdev_priv(netdev);
+	struct netdev_hw_addr *ha;
+	int index = 0;
+
+	if (count <= 0) {
+		priv->mcaddr_list.count = 0;
+		return;
+	}
+
+	netdev_for_each_mc_addr(ha, netdev) {
+		if (!is_multicast_ether_addr(ha->addr))
+			continue;

Is this possible?

I remember I've seen this in one of the drivers I have studied, but
I'm not really sure it is actually necessary. I added it to be on the
safe side..

quoted

+
+		WARN_ON(index >= OWL_EMAC_MAX_MULTICAST_ADDRS);
+		ether_addr_copy(priv->mcaddr_list.addrs[index++], ha->addr);
+	}
+
+	priv->mcaddr_list.count = index;
+
+	owl_emac_setup_frame_xmit(priv);
+}
+
+static void owl_emac_ndo_set_rx_mode(struct net_device *netdev)
+{
+	struct owl_emac_priv *priv = netdev_priv(netdev);
+	u32 status, val = 0;
+	int mcast_count = 0;
+
+	if (netdev->flags & IFF_PROMISC) {
+		val = OWL_EMAC_BIT_MAC_CSR6_PR;
+	} else if (netdev->flags & IFF_ALLMULTI) {
+		val = OWL_EMAC_BIT_MAC_CSR6_PM;
+	} else if (netdev->flags & IFF_MULTICAST) {
+		mcast_count = netdev_mc_count(netdev);
+
+		if (mcast_count > OWL_EMAC_MAX_MULTICAST_ADDRS) {
+			val = OWL_EMAC_BIT_MAC_CSR6_PM;
+			mcast_count = 0;
+		}
+	}
+
+	spin_lock_bh(&priv->lock);
+
+	/* Temporarily stop DMA TX & RX. */
+	status = owl_emac_dma_cmd_stop(priv);
+
+	/* Update operation modes. */
+	owl_emac_reg_update(priv, OWL_EMAC_REG_MAC_CSR6,
+			    OWL_EMAC_BIT_MAC_CSR6_PR | OWL_EMAC_BIT_MAC_CSR6_PM,
+			    val);
+
+	/* Restore DMA TX & RX status. */
+	owl_emac_dma_cmd_set(priv, status);
+
+	spin_unlock_bh(&priv->lock);
+
+	/* Set/reset multicast addr list. */
+	owl_emac_set_multicast(netdev, mcast_count);
+}

I think this can be simplified. At least, you had me going around in
circles a while trying to see if WARN_ON() could be triggered from
user space.

If you have more than OWL_EMAC_MAX_MULTICAST_ADDRS MC addresses, you
go into promisc mode. Can you then skip calling
owl_emac_set_multicast(), which appears not to do too much useful when
passed 0?

The main purpose of always calling owl_emac_set_multicast() is to ensure
the size of the mcaddr_list is correctly updated (either set or reset).
This prevents owl_emac_setup_frame_xmit() using obsolete data, when
invoked from different contexts (i.e. MAC address changed).

A conditional call involves splitting the mcaddr_list management logic
(i.e. moving the 'reset' operation from the callee to the caller), which
IMO would make the usage of a separate function less justified.

Thanks,
Cristi

       Andrew