mlxsw: spectrum_qdisc: Clarify a comment

	.clean_stats = mlxsw_sp_setup_tc_qdisc_prio_clean_stats,

};

/* Grafting is not supported in mlxsw. It will result in un-offloading of the

 * grafted qdisc as well as the qdisc in the qdisc new location.

 * (However, if the graft is to the location where the qdisc is already at, it

 * will be ignored completely and won't cause un-offloading).

/* Linux allows linking of Qdiscs to arbitrary classes (so long as the resulting

 * graph is free of cycles). These operations do not change the parent handle

 * though, which means it can be incomplete (if there is more than one class

 * where the Qdisc in question is grafted) or outright wrong (if the Qdisc was

 * linked to a different class and then removed from the original class).

 *

 * E.g. consider this sequence of operations:

 *

 *  # tc qdisc add dev swp1 root handle 1: prio

 *  # tc qdisc add dev swp1 parent 1:3 handle 13: red limit 1000000 avpkt 10000

 *  RED: set bandwidth to 10Mbit

 *  # tc qdisc link dev swp1 handle 13: parent 1:2

 *

 * At this point, both 1:2 and 1:3 have the same RED Qdisc instance as their

 * child. But RED will still only claim that 1:3 is its parent. If it's removed

 * from that band, its only parent will be 1:2, but it will continue to claim

 * that it is in fact 1:3.

 *

 * The notification for child Qdisc replace (e.g. TC_RED_REPLACE) comes before

 * the notification for parent graft (e.g. TC_PRIO_GRAFT). We take the replace

 * notification to offload the child Qdisc, based on its parent handle, and use

 * the graft operation to validate that the class where the child is actually

 * grafted corresponds to the parent handle. If the two don't match, we

 * unoffload the child.

 */

static int

mlxsw_sp_qdisc_prio_graft(struct mlxsw_sp_port *mlxsw_sp_port,

	int tclass_num = MLXSW_SP_PRIO_BAND_TO_TCLASS(p->band);

	struct mlxsw_sp_qdisc *old_qdisc;

	/* Check if the grafted qdisc is already in its "new" location. If so -

	 * nothing needs to be done.

	 */

	if (p->band < IEEE_8021QAZ_MAX_TCS &&

	    mlxsw_sp_port->tclass_qdiscs[tclass_num].handle == p->child_handle)

		return 0;