net/sched: taprio: allow user input of per-tc max SDU

IEEE 802.1Q clause 12.29.1.1 "The queueMaxSDUTable structure and data
types" and 8.6.8.4 "Enhancements for scheduled traffic" talk about the
existence of a per traffic class limitation of maximum frame sizes, with
a fallback on the port-based MTU.

As far as I am able to understand, the 802.1Q Service Data Unit (SDU)
represents the MAC Service Data Unit (MSDU, i.e. L2 payload), excluding
any number of prepended VLAN headers which may be otherwise present in
the MSDU. Therefore, the queueMaxSDU is directly comparable to the
device MTU (1500 means L2 payload sizes are accepted, or frame sizes of
1518 octets, or 1522 plus one VLAN header). Drivers which offload this
are directly responsible of translating into other units of measurement.

To keep the fast path checks optimized, we keep 2 arrays in the qdisc,
one for max_sdu translated into frame length (so that it's comparable to
skb->len), and another for offloading and for dumping back to the user.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 34600292fdfb..38207873eda6 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -160,6 +160,10 @@ struct tc_etf_qopt_offload {
 	s32 queue;
 };
 
+struct tc_taprio_caps {
+	bool supports_queue_max_sdu:1;
+};
+
 struct tc_taprio_sched_entry {
 	u8 command; /* TC_TAPRIO_CMD_* */
 
@@ -173,6 +177,7 @@ struct tc_taprio_qopt_offload {
 	ktime_t base_time;
 	u64 cycle_time;
 	u64 cycle_time_extension;
+	u32 max_sdu[TC_MAX_QUEUE];
 
 	size_t num_entries;
 	struct tc_taprio_sched_entry entries[];