nfp: abm: remember which Qdisc is root

Keep track of which Qdisc is currently root.  We need to implement
TC_SETUP_ROOT_QDISC handling, and for completeness also clear the
root Qdisc pointer when it's freed.  TC_SETUP_ROOT_QDISC isn't always
sent when device is dismantled.

Remembering the root Qdisc will allow us to build the entire hierarchy
in following patches.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: John Hurley <john.hurley@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/abm/main.c

@@ -37,6 +37,8 @@ nfp_abm_setup_tc(struct nfp_app *app, struct net_device *netdev,
 		return -EOPNOTSUPP;
 
 	switch (type) {
+	case TC_SETUP_ROOT_QDISC:
+		return nfp_abm_setup_root(netdev, repr->app_priv, type_data);
 	case TC_SETUP_QDISC_MQ:
 		return nfp_abm_setup_tc_mq(netdev, repr->app_priv, type_data);
 	case TC_SETUP_QDISC_RED:

drivers/net/ethernet/netronome/nfp/abm/main.h

@@ -116,6 +116,7 @@ struct nfp_red_qdisc {
  * @parent:	handle of expected parent, i.e. handle of MQ, or TC_H_ROOT
  * @num_qdiscs:	number of currently used qdiscs
  * @red_qdiscs:	array of qdiscs
+ * @root_qdisc:	pointer to the current root of the Qdisc hierarchy
  * @qdiscs:	all qdiscs recorded by major part of the handle
  */
 struct nfp_abm_link {
@@ -127,9 +128,12 @@ struct nfp_abm_link {
 	u32 parent;
 	unsigned int num_qdiscs;
 	struct nfp_red_qdisc *red_qdiscs;
+	struct nfp_qdisc *root_qdisc;
 	struct radix_tree_root qdiscs;
 };
 
+int nfp_abm_setup_root(struct net_device *netdev, struct nfp_abm_link *alink,
+		       struct tc_root_qopt_offload *opt);
 int nfp_abm_setup_tc_red(struct net_device *netdev, struct nfp_abm_link *alink,
 			 struct tc_red_qopt_offload *opt);
 int nfp_abm_setup_tc_mq(struct net_device *netdev, struct nfp_abm_link *alink,

drivers/net/ethernet/netronome/nfp/abm/qdisc.c

@@ -143,6 +143,9 @@ nfp_abm_qdisc_destroy(struct net_device *netdev, struct nfp_abm_link *alink,
 		return;
 
 	nfp_abm_qdisc_free(netdev, alink, qdisc);
+
+	if (alink->root_qdisc == qdisc)
+		alink->root_qdisc = NULL;
 }
 
 static void
@@ -450,3 +453,13 @@ int nfp_abm_setup_tc_mq(struct net_device *netdev, struct nfp_abm_link *alink,
 		return -EOPNOTSUPP;
 	}
 }
+
+int nfp_abm_setup_root(struct net_device *netdev, struct nfp_abm_link *alink,
+		       struct tc_root_qopt_offload *opt)
+{
+	if (opt->ingress)
+		return -EOPNOTSUPP;
+	alink->root_qdisc = nfp_abm_qdisc_find(alink, opt->handle);
+
+	return 0;
+}