[PATCH net v2 1/3] net: airoha: handle RX_NO_CPU_DSCP interrupt, not just RX_DONE

[Vitaliy Sochnev <sochnev.v.74@gmail.com>]

airoha_qdma_hw_init() unmasks the per-ring NO_CPU_DSCP interrupt, which
fires when an RX ring runs out of free CPU descriptors, but
airoha_irq_handler() only extracts the RX_DONE bits from the same status
word. The NO_CPU_DSCP bits are acknowledged and dropped.

Once a ring is drained to zero posted descriptors no further RX_DONE can
fire for it - nothing is left for hw to receive into - so NAPI is never
rescheduled, airoha_qdma_fill_rx_queue() is never called again, and the
ring stays dead until the interface is reconfigured.

This is reachable on RX ring 4, which airoha_fe_vip_setup() force-routes
~15 VIP-classified protocols onto (BOOTP, PPPoE Discovery, ISAKMP,
DHCPv6, SIP, LLDP, PPP LCP/IPCP/CHAP/PAP/IPv6CP, ...) while it sits on
the 16-descriptor RX_DSCP_NUM() default. A DHCP renewal or a PPPoE
negotiation burst drains it faster than the CPU reposts, after which all
of those protocols silently stop being received.

Treat NO_CPU_DSCP like RX_DONE for scheduling NAPI:
airoha_qdma_rx_process() already calls airoha_qdma_fill_rx_queue()
unconditionally at the end of every poll, so scheduling NAPI is enough
to make an emptied ring refill itself. Re-enable the bit alongside
RX_DONE in airoha_qdma_rx_napi_poll() so it is not left masked after
first use.

Whether NO_CPU_DSCP re-latches while the ring is still empty is not
documented. If it does, a ring that cannot be refilled (page_pool
returning NULL) keeps reasserting it. Masking it until a refill succeeds
is worse: a starved ring never fires RX_DONE either, so it would stay
dead after the memory pressure clears.

Fixes: f252493e1835 ("net: airoha: Enable multiple IRQ lines support in airoha_eth driver.")
Link: https://github.com/openwrt/openwrt/issues/24715
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Vitaliy Sochnev <sochnev.v.74@gmail.com>
---
 drivers/net/ethernet/airoha/airoha_eth.c  | 16 +++++++++++-----
 drivers/net/ethernet/airoha/airoha_regs.h |  2 ++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
index 64619e9a704d..c59201aded26 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.c
+++ b/drivers/net/ethernet/airoha/airoha_eth.c
@@ -784,13 +784,16 @@ static int airoha_qdma_rx_napi_poll(struct napi_struct *napi, int budget)
 		int i, qid = q - &qdma->q_rx[0];
 		int intr_reg = qid < RX_DONE_HIGH_OFFSET ? QDMA_INT_REG_IDX1
 							 : QDMA_INT_REG_IDX2;
+		u32 irq_id = qid % RX_DONE_HIGH_OFFSET;
+		u32 intr_mask = BIT(irq_id) |
+				BIT(irq_id + RX_NO_CPU_DSCP_LOW_OFFSET);
 
 		for (i = 0; i < ARRAY_SIZE(qdma->irq_banks); i++) {
 			if (!(BIT(qid) & RX_IRQ_BANK_PIN_MASK(i)))
 				continue;
 
 			airoha_qdma_irq_enable(&qdma->irq_banks[i], intr_reg,
-					       BIT(qid % RX_DONE_HIGH_OFFSET));
+					       intr_mask);
 		}
 	}
 
@@ -1468,16 +1471,19 @@ static irqreturn_t airoha_irq_handler(int irq, void *dev_instance)
 	if (!test_bit(DEV_STATE_INITIALIZED, &qdma->eth->state))
 		return IRQ_NONE;
 
-	rx_intr1 = intr[1] & RX_DONE_LOW_INT_MASK;
+	rx_intr1 = intr[1] & (RX_DONE_LOW_INT_MASK | RX_NO_CPU_DSCP_LOW_INT_MASK);
 	if (rx_intr1) {
 		airoha_qdma_irq_disable(irq_bank, QDMA_INT_REG_IDX1, rx_intr1);
-		rx_intr_mask |= rx_intr1;
+		rx_intr_mask |= (rx_intr1 & RX_DONE_LOW_INT_MASK) |
+				RX_NO_CPU_DSCP_INT_RX1_MASK(rx_intr1);
 	}
 
-	rx_intr2 = intr[2] & RX_DONE_HIGH_INT_MASK;
+	rx_intr2 = intr[2] & (RX_DONE_HIGH_INT_MASK | RX_NO_CPU_DSCP_HIGH_INT_MASK);
 	if (rx_intr2) {
 		airoha_qdma_irq_disable(irq_bank, QDMA_INT_REG_IDX2, rx_intr2);
-		rx_intr_mask |= (rx_intr2 << 16);
+		rx_intr_mask |= ((rx_intr2 & RX_DONE_HIGH_INT_MASK) <<
+				 RX_DONE_HIGH_OFFSET) |
+				(rx_intr2 & RX_NO_CPU_DSCP_HIGH_INT_MASK);
 	}
 
 	for (i = 0; rx_intr_mask && i < ARRAY_SIZE(qdma->q_rx); i++) {
diff --git a/drivers/net/ethernet/airoha/airoha_regs.h b/drivers/net/ethernet/airoha/airoha_regs.h
index 442b48c9b991..bde3d599d8b7 100644
--- a/drivers/net/ethernet/airoha/airoha_regs.h
+++ b/drivers/net/ethernet/airoha/airoha_regs.h
@@ -549,6 +549,8 @@
 #define INT_RX1_MASK(_n)							\
 	((((_n) << RX_NO_CPU_DSCP_LOW_OFFSET) & RX_NO_CPU_DSCP_LOW_INT_MASK) |	\
 	 (RX_DONE_LOW_INT_MASK & (_n)))
+#define RX_NO_CPU_DSCP_INT_RX1_MASK(_n)					\
+	(((_n) & RX_NO_CPU_DSCP_LOW_INT_MASK) >> RX_NO_CPU_DSCP_LOW_OFFSET)
 
 /* QDMA_CSR_INT_ENABLE3 */
 #define RX31_NO_CPU_DSCP_INT_MASK	BIT(31)
-- 
2.55.0