[PATCH net-next 4/4] net: airoha: grow RX ring 4 to 128 descriptors

[Vitaliy Sochnev]

Ring 4 is the shared "force to CPU" ring for a wide set of protocols
(BOOTP, PPPoE Discovery, PPP LCP/IPCP/CHAP/IPv6CP/PAP, ISAKMP, DHCPv6,
SIP, LLDP, ...) and currently falls into the 16-descriptor default in
RX_DSCP_NUM(), same as most other non-hashed rings. The hw completion
race recovered by airoha_qdma_rx_check_stall()/rx_recover_work() in
the previous commits appears strongly correlated with a ring going
from idle to receiving its first frame(s) - exactly the access pattern
this shared ring sees under protocol negotiation bursts. Give it the
same 128-descriptor allowance already used for rings 2/11/15, matching
the other rings that see bursty, non-hashed traffic, to reduce how
often that condition is hit in the first place.

Ring 4 and the VIP classification that forces these protocols onto it
are shared driver-wide, with no DT/hardware property distinguishing
one chip variant's ring 4 from another's, so this isn't scoped to
AN7583 specifically even though that's where the race was found and
reproduced. 24h+ stress runs forcing repeated PPPoE/DHCP renegotiation
on an AN7581 board, both with and without the two preceding fixes,
completed 570+ forced reconnect cycles each with no regressions from
the larger ring.

Signed-off-by: Vitaliy Sochnev <sochnev.v.74@xxxxxxxxx>
---
 drivers/net/ethernet/airoha/airoha_eth.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/airoha/airoha_eth.h b/drivers/net/ethernet/airoha/airoha_eth.h
index d6591a779743..cd75c16d8d0c 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.h
+++ b/drivers/net/ethernet/airoha/airoha_eth.h
@@ -41,6 +41,7 @@
 #define TX_DSCP_NUM			1024
 #define RX_DSCP_NUM(_n)			\
 	((_n) ==  2 ? 128 :		\
+	 (_n) ==  4 ? 128 :		\
 	 (_n) == 11 ? 128 :		\
 	 (_n) == 15 ? 128 :		\
 	 (_n) ==  0 ? 1024 : 16)
-- 
2.55.0