net: ti: am65-cpsw-nuss: fix RX IRQ state after .ndo_stop()

On TI K3 am64x platform the issue with RX IRQ is observed - it's become
disabled forever after .ndo_stop(). The K3 CPSW driver manipulates RX IRQ
by using standard Linux enable_irq()/disable_irq_nosync() API as there is
no IRQ enable/disable options in CPSW HW itself, as result during
.ndo_stop() following sequence happens

  phy_stop()
  teardown TX/RX channels
  wait for TX tdown complete
  napi_disable(TX)
  clean up TX channels

  (a)

  napi_disable(RX)

At point (a) it's not possible to predict if RX IRQ was triggered or not.
if RX IRQ was triggered then it also not possible to definitely say if RX
NAPI was run or only scheduled and immediately canceled by
napi_disable(RX). Actually the last case causes RX IRQ to be permanently
disabled.

Another observed issue is that RX IRQ enable counter become unbalanced if
(gro_flush_timeout =! 0) while (napi_defer_hard_irqs == 0):

Unbalanced enable for IRQ 44
WARNING: CPU: 0 PID: 10 at ../kernel/irq/manage.c:776 __enable_irq+0x38/0x80
__enable_irq+0x38/0x80
enable_irq+0x54/0xb0
am65_cpsw_nuss_rx_poll+0x2f4/0x368
__napi_poll+0x34/0x1b8
net_rx_action+0xe4/0x220
_stext+0x11c/0x284
run_ksoftirqd+0x4c/0x60

To avoid above issues introduce flag indicating if RX was actually disabled
before enabling it in am65_cpsw_nuss_rx_poll() and restore RX IRQ state in
.ndo_open()

Fixes: 4f7cce27 ("net: ethernet: ti: am65-cpsw: add support for am64x cpsw3g")
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/am65-cpsw-nuss.c

@@ -519,6 +519,10 @@ static int am65_cpsw_nuss_common_open(struct am65_cpsw_common *common,
 	}
 
 	napi_enable(&common->napi_rx);
+	if (common->rx_irq_disabled) {
+		common->rx_irq_disabled = false;
+		enable_irq(common->rx_chns.irq);
+	}
 
 	dev_dbg(common->dev, "cpsw_nuss started\n");
 	return 0;
@@ -872,8 +876,12 @@ static int am65_cpsw_nuss_rx_poll(struct napi_struct *napi_rx, int budget)
 
 	dev_dbg(common->dev, "%s num_rx:%d %d\n", __func__, num_rx, budget);
 
-	if (num_rx < budget && napi_complete_done(napi_rx, num_rx))
-		enable_irq(common->rx_chns.irq);
+	if (num_rx < budget && napi_complete_done(napi_rx, num_rx)) {
+		if (common->rx_irq_disabled) {
+			common->rx_irq_disabled = false;
+			enable_irq(common->rx_chns.irq);
+		}
+	}
 
 	return num_rx;
 }
@@ -1091,6 +1099,7 @@ static irqreturn_t am65_cpsw_nuss_rx_irq(int irq, void *dev_id)
 {
 	struct am65_cpsw_common *common = dev_id;
 
+	common->rx_irq_disabled = true;
 	disable_irq_nosync(irq);
 	napi_schedule(&common->napi_rx);
 

drivers/net/ethernet/ti/am65-cpsw-nuss.h

@@ -126,6 +126,8 @@ struct am65_cpsw_common {
 	struct am65_cpsw_rx_chn	rx_chns;
 	struct napi_struct	napi_rx;
 
+	bool			rx_irq_disabled;
+
 	u32			nuss_ver;
 	u32			cpsw_ver;
 	unsigned long		bus_freq;