[PATCH net v2] net: txgbe: fix MISC interrupt unmasking in non-MSI-X mode and device shutdown

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.

Additionally, unconditionally unmasking the interrupt at the end of the
thread introduces a race condition during device teardown. Guarding the
wx_intr_enable() call with a check for the WX_STATE_DOWN bit, to prevent
re-arming the interrupt during device shutdown.

Fixes: e37546ad1f9b ("net: wangxun: revert the adjustment of the IRQ vector sequence")
Signed-off-by: Jiawen Wu <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
---
Changes in v2:
- Add the checking of WX_STATE_DOWN bit before unmasking the interrupt.
- Link to v1: https://lore.kernel.org/all/[email protected]
---
 drivers/net/ethernet/wangxun/txgbe/txgbe_irq.c | 5 ++++-
 1 file changed, 4 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..5ad1ff7c3ce9 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 +184,9 @@ 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);
+	if (!test_bit(WX_STATE_DOWN, wx->state))
+		wx_intr_enable(wx, misc_mask);
 	return (nhandled > 0 ? IRQ_HANDLED : IRQ_NONE);
 }
 
-- 
2.51.0