From: CachyOS/NixOS-CachyOS
Subject: [PATCH] net/tcp: add TCP_CONG_WANTS_CE_EVENTS for Asahi tree compat

The CachyOS 6.18 base patch adds TCP_CONG_WANTS_CE_EVENTS at BIT(2) and
a tcp_ca_wants_ce_events() helper in include/net/tcp.h, and updates
tcp_bbr.c and tcp_input.c to use them.

The Asahi linux tree already occupies BIT(2)–BIT(4) with AccECN flags
(TCP_CONG_NEEDS_ACCECN, TCP_CONG_ECT_1_NEGOTIATION,
TCP_CONG_NO_FALLBACK_RFC3168), so the CachyOS hunk that defines
TCP_CONG_WANTS_CE_EVENTS fails to apply, while the later hunks that
*use* it (tcp_ca_wants_ce_events(), tcp_bbr.c .flags) succeed, leaving
a dangling undefined-identifier compile error.

Fix: define TCP_CONG_WANTS_CE_EVENTS at BIT(5) (the next free bit after
the AccECN flags) and add it to TCP_CONG_MASK. The tcp_ca_wants_ce_events()
helper and tcp_bbr.c / tcp_input.c callers are already in place from the
CachyOS patch, so this is sufficient to resolve the build error.

--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1198,6 +1198,10 @@ enum tcp_ca_ack_event_flags {
 /* Cannot fallback to RFC3168 during AccECN negotiation */
 #define TCP_CONG_NO_FALLBACK_RFC3168	BIT(4)
+/* Wants notification of CE events (CA_EVENT_ECN_IS_CE, CA_EVENT_ECN_NO_CE).
+ * BIT(2)–BIT(4) are taken by AccECN flags in the Asahi tree. */
+#define TCP_CONG_WANTS_CE_EVENTS	BIT(5)
 #define TCP_CONG_MASK  (TCP_CONG_NON_RESTRICTED | TCP_CONG_NEEDS_ECN | \
-			TCP_CONG_NEEDS_ACCECN | TCP_CONG_ECT_1_NEGOTIATION | \
-			TCP_CONG_NO_FALLBACK_RFC3168)
+			TCP_CONG_NEEDS_ACCECN | TCP_CONG_ECT_1_NEGOTIATION | \
+			TCP_CONG_NO_FALLBACK_RFC3168 | TCP_CONG_WANTS_CE_EVENTS)