[PATCH net] net: txgbe: fix interrupt mask for MISC cause in non-MSI-X mode

In txgbe_misc_irq_thread_fn(), the driver unmasks the miscellaneous
interrupt at the end of the handler using TXGBE_INTR_MISC(wx) (which
resolves to BIT(wx->num_q_vectors)). While this is correct for MSI-X
mode, it is incorrect for legacy INTx or single MSI modes.

Due to hardware behavior, the WX_PX_MISC_IVAR register is completely
ignored by the hardware when MSI-X is disabled. In non-MSI-X mode, the
hardware forcibly merges all interrupt causes (both Queue and MISC) into
a single bit: BIT(0) of the interrupt register.

Unconditionally unmasking TXGBE_INTR_MISC(wx) (e.g., BIT(1)) in non-MSI-X
mode means the actual MISC interrupt bit (BIT(0)) is not unmasked
promptly at the end of the MISC thread. Instead, it remains masked until
NAPI completes its polling and unmasks the shared BIT(0). This delays the
assertion of subsequent MISC interrupts, preventing timely handling of
events like link state changes.

Fix this by explicitly checking `pdev->msix_enabled` and falling back
to BIT(0) as the interrupt mask for the MISC cause when MSI-X is disabled.

Fixes: e37546ad1f9b ("net: wangxun: revert the adjustment of the IRQ vector sequence")
Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
---
 drivers/net/ethernet/wangxun/txgbe/txgbe_irq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/wangxun/txgbe/txgbe_irq.c b/drivers/net/ethernet/wangxun/txgbe/txgbe_irq.c
index 8746318ad3bc..05b318f4e6ed 100644
--- a/drivers/net/ethernet/wangxun/txgbe/txgbe_irq.c
+++ b/drivers/net/ethernet/wangxun/txgbe/txgbe_irq.c

@@ -164,6 +164,7 @@ static irqreturn_t txgbe_misc_irq_thread_fn(int irq, void *data)
 	struct wx *wx = txgbe->wx;
 	unsigned int nhandled = 0;
 	unsigned int sub_irq;
+	u64 misc_mask;
 	u32 eicr;
 
 	eicr = txgbe->eicr;

@@ -183,7 +184,8 @@ static irqreturn_t txgbe_misc_irq_thread_fn(int irq, void *data)
 		nhandled++;
 	}
 
-	wx_intr_enable(wx, TXGBE_INTR_MISC(wx));
+	misc_mask = wx->pdev->msix_enabled ? TXGBE_INTR_MISC(wx) : BIT(0);
+	wx_intr_enable(wx, misc_mask);
 	return (nhandled > 0 ? IRQ_HANDLED : IRQ_NONE);
 }
 

-- 
2.51.0