It has shown FLOW_ACTION_POLICE is not stable, and it's very likely that
options were added at drivers' request.

However, that also means .port_policer_add() would have to check the
parameters themselves. Giving that struct dsa_mall_policer_tc_entry is
not stable, adjusting the interface between the framework and drivers
would be a pain.

Introduce a helper to maximize forward compatibility. Drivers may use it
to recognize the pattern of tc entry reliably, and ensure all
newly-added options are set to 0 / their default values and do not break
the semantics.

Signed-off-by: David Yang <mmyangfl@gmail.com>
---
 include/net/dsa.h | 14 ++++++++++++++
 net/dsa/dsa.c     | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 4c177b168ec8..957439846fe5 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -1410,4 +1410,18 @@ netdev_tx_t dsa_enqueue_skb(struct sk_buff *skb, struct net_device *dev);
 void dsa_port_phylink_mac_change(struct dsa_switch *ds, int port, bool up);
 bool dsa_supports_eee(struct dsa_switch *ds, int port);
 
+enum dsa_mall_policer_tc_type {
+	/* Pattern recognized, no surprising fields exist */
+	DSA_MALL_POLICER_TC_KNOWN = BIT(0),
+	/* Unset: .burst and .rate_bytes_per_sec valid
+	 * Set: .burst_pkt and .rate_pkt_ps valid
+	 */
+	DSA_MALL_POLICER_TC_PKT_MODE = BIT(1),
+	/* .mtu valid */
+	DSA_MALL_POLICER_TC_MTU = BIT(2),
+};
+
+unsigned long
+dsa_mall_policer_tc_entry_type(struct dsa_mall_policer_tc_entry *entry);
+
 #endif
diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
index 35ce3941fae3..c8102cea5ab3 100644
--- a/net/dsa/dsa.c
+++ b/net/dsa/dsa.c
@@ -1834,6 +1834,39 @@ int dsa_port_simple_hsr_leave(struct dsa_switch *ds, int port,
 }
 EXPORT_SYMBOL_GPL(dsa_port_simple_hsr_leave);
 
+/* dsa_mall_policer_tc_entry_type - map tc_entry to some "known" types
+ * @entry: the tc entry
+ *
+ * A helper to check dsa_mall_policer_tc_entry against some known patterns,
+ * without having to know the exact struct layout.
+ *
+ * Returns: ORs of enum dsa_mall_policer_tc_type with DSA_MALL_POLICER_TC_KNOWN
+ * set if recognized, otherwise 0
+ */
+unsigned long
+dsa_mall_policer_tc_entry_type(struct dsa_mall_policer_tc_entry *entry)
+{
+	bool byte_mode = (entry->burst || entry->rate_bytes_per_sec);
+	bool pkt_mode = (entry->burst_pkt || entry->rate_pkt_ps);
+	unsigned long flags = DSA_MALL_POLICER_TC_KNOWN;
+
+	if (byte_mode == pkt_mode)
+		return 0;
+	if (entry->peakrate_bytes_ps || entry->avrate || entry->overhead)
+		return 0;
+	if (entry->exceed.act_id != FLOW_ACTION_DROP ||
+	    entry->notexceed.act_id != FLOW_ACTION_ACCEPT)
+		return 0;
+
+	if (pkt_mode)
+		flags |= DSA_MALL_POLICER_TC_PKT_MODE;
+	if (entry->mtu)
+		flags |= DSA_MALL_POLICER_TC_MTU;
+
+	return flags;
+}
+EXPORT_SYMBOL_GPL(dsa_mall_policer_tc_entry_type);
+
 static const struct dsa_stubs __dsa_stubs = {
 	.conduit_hwtstamp_validate = __dsa_conduit_hwtstamp_validate,
 };
-- 
2.51.0