[PATCH net v3 2/2] net: airoha: grow the small RX rings

Raise the RX_DSCP_NUM() fallback from 16 to 32, the vendor SDK default,
and give ring 4 the 128 descriptors already used for rings 2/11/15.

Ring 4 is the shared "force to CPU" ring that airoha_fe_vip_setup()
routes BOOTP, PPPoE Discovery, PPP LCP/IPCP/CHAP/PAP/IPv6CP, ISAKMP,
DHCPv6, SIP and LLDP onto, so it sees the same bursty non-hashed traffic
as the rings already on 128 while sitting on the smallest allowance.
Both CDMs forward to it: REG_CDM_FWD_CFG(1) and (2) each set
CDM_VIP_QSEL_MASK to 4.

The NO_CPU_DSCP fix does not cover this. With it in place, at 16
descriptors the ring still dies during PPPoE negotiation on a Nokia
XG-040G-MF: over 6455 devmem samples in 60 s, REG_RX_DMA_IDX advanced
0x2c -> 0x52 while REG_RX_CPU_IDX stayed at 15, descriptor 15 had DONE
set on a 60-byte frame, descriptors 0-14 were empty, and q->tail was 0.
Hw had completed a descriptor the strictly sequential consumer in
airoha_qdma_rx_process() cannot reach, and negotiation never completes.
At 16 DHCP still works while PPPoE does not: a dial-up bursts Discovery,
LCP, IPCP and CHAP where DHCP sends one packet every ~150 s. With this
series, 508 forced reconnects over 20 h saw no recurrence.

RX_DONE_INT_MASK covers all 32 rings on both QDMA instances, so this
costs 544 more descriptors per instance, 1088 in total: 2.1 MiB of RX
buffers at PAGE_SIZE/2 each, plus 34 KiB of coherent descriptor memory.

Ring 4 and the VIP classification feeding it are shared driver-wide, with
no DT or hardware property distinguishing one variant's ring 4 from
another's, so this is not scoped to a particular SoC.

Fixes: 23020f049327 ("net: airoha: Introduce ethernet support for EN7581 SoC")
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Vitaliy Sochnev <redacted>
---
 drivers/net/ethernet/airoha/airoha_eth.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/airoha/airoha_eth.h b/drivers/net/ethernet/airoha/airoha_eth.h
index fa9a8edce22f..7fc37f159d2b 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.h
+++ b/drivers/net/ethernet/airoha/airoha_eth.h

@@ -41,9 +41,10 @@
 #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)
+	 (_n) ==  0 ? 1024 : 32)
 
 #define PSE_RSV_PAGES			128
 #define PSE_QUEUE_RSV_PAGES		64

-- 
2.55.0