ramips: fix MT7621 switch driver IRQ storm on init with linux 4.14

The hardware emits some interrupts while initializing and handling them
can mess up the state or cause infinite loops.
Fix this by disabling IRQs during init and re-enabling them afterwards

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/ramips/files-4.14/drivers/net/ethernet/mtk/gsw_mt7621.c

@@ -41,6 +41,7 @@ static irqreturn_t gsw_interrupt_mt7621(int irq, void *_priv)
 	u32 reg, i;
 
 	reg = mt7530_mdio_r32(gsw, 0x700c);
+	mt7530_mdio_w32(gsw, 0x700c, reg);
 
 	for (i = 0; i < 5; i++)
 		if (reg & BIT(i)) {
@@ -61,7 +62,6 @@ static irqreturn_t gsw_interrupt_mt7621(int irq, void *_priv)
 		}
 
 	mt7620_handle_carrier(priv);
-	mt7530_mdio_w32(gsw, 0x700c, 0x1f);
 
 	return IRQ_HANDLED;
 }
@@ -193,9 +193,8 @@ static void mt7621_hw_init(struct mt7620_gsw *gsw, struct device_node *np)
 		_mt7620_mii_write(gsw, i, 0, val);
 	}
 
-	/* mask irq */
-	mt7530_mdio_w32(gsw, 0x7008, 0x1f);
 	/* enable irq */
+	mt7530_mdio_w32(gsw, 0x7008, 0x1f);
 	val = mt7530_mdio_r32(gsw, 0x7808);
 	val |= 3 << 16;
 	mt7530_mdio_w32(gsw, 0x7808, val);
@@ -225,10 +224,14 @@ int mtk_gsw_init(struct fe_priv *priv)
 	if (gsw->irq) {
 		request_irq(gsw->irq, gsw_interrupt_mt7621, 0,
 			    "gsw", priv);
-		mt7530_mdio_w32(gsw, 0x7008, ~0x1f);
+		disable_irq(gsw->irq);
 	}
+
 	mt7621_hw_init(gsw, np);
 
+	if (gsw->irq)
+		enable_irq(gsw->irq);
+
 	return 0;
 }