On Fri, Dec 04, 2020 at 03:20, Andrew Lunn [off-list ref] wrote:

quoted

+static int dsa_tree_setup_lags(struct dsa_switch_tree *dst)
+{
+	struct dsa_port *dp;
+	unsigned int num;
+
+	list_for_each_entry(dp, &dst->ports, list)
+		num = dp->ds->num_lags;
+
+	list_for_each_entry(dp, &dst->ports, list)
+		num = min(num, dp->ds->num_lags);

Do you really need to loop over the list twice? Cannot num be
initialised to UINT_MAX and then just do the second loop.

I was mostly paranoid about the case where, for some reason, the list of
ports was empty due to an invalid DT or something. But I now see that
since num is not initialized, that would not have helped.

So, is my paranoia valid, i.e. fix is `unsigned int num = 0`? Or can
that never happen, i.e. fix is to initialize to UINT_MAX and remove
first loop?

quoted

+static inline bool dsa_port_can_offload(struct dsa_port *dp,
+					struct net_device *dev)

That name is a bit generic. We have a number of different offloads.
The mv88E6060 cannot offload anything!

The name is intentionally generic as it answers the question "can this
dp offload requests for this netdev?"

quoted

+{
+	/* Switchdev offloading can be configured on: */
+
+	if (dev == dp->slave)
+		/* DSA ports directly connected to a bridge. */
+		return true;

This condition is the normal case of a bridged port, i.e. no LAG
involved.

quoted

+	if (dp->lag && dev == rtnl_dereference(dp->lag->dev))
+		/* DSA ports connected to a bridge via a LAG */
+		return true;

And then the indirect case of a bridged port under a LAG.

I am happy to take requests for a better name though.

quoted

+	return false;
+}

quoted

+static void dsa_lag_put(struct dsa_switch_tree *dst, struct dsa_lag *lag)
+{
+	if (!refcount_dec_and_test(&lag->refcount))
+		return;
+
+	clear_bit(lag->id, dst->lags.busy);
+	WRITE_ONCE(lag->dev, NULL);
+	memset(lag, 0, sizeof(*lag));
+}

I don't know what the locking is here, but wouldn't it be safer to
clear the bit last, after the memset and WRITE_ONCE.

All writers of dst->lags.busy are serialized with respect to dsa_lag_put
(on rtnl_lock), and concurrent readers (dsa_lag_dev_by_id) start by
checking busy before reading lag->dev. To my understanding, WRITE_ONCE
would insert the proper fence to make sure busy was cleared before
clearing dev?

    Andrew