[PATCH v2] net: mvneta: free/request IRQ across suspend/resume

[Yun Zhou <yun.zhou@windriver.com>]

On PREEMPT_RT, the mvneta IRQ handler is force-threaded. Under high
network traffic, the IRQ can enter suspend with desc->depth == 1
(masked by the oneshot mechanism between handler invocations).

During suspend, the kernel increments depth to 2 and masks the
interrupt at the MPIC level (clearing the SRC_CTL CPU routing bit,
due to IRQCHIP_MASK_ON_SUSPEND). On resume, depth is decremented
back to 1, but since it does not reach 0, the unmask is never
called. The MPIC CPU routing remains cleared, permanently disabling
interrupt delivery.

Fix by freeing the IRQ in suspend and re-requesting it in resume.
This ensures a clean IRQ state (depth=0, proper hardware routing)
on every resume cycle, regardless of the pre-suspend depth. This
follows the approach used by other drivers (e.g. igb).

Fixes: 9768b45ceb0b ("net: mvneta: support suspend and resume")
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
---
v2:
  - Move request_irq before cpuhp registration in resume (matching
    mvneta_open ordering) so that failure does not leave cpuhp
    callbacks registered on a non-functional device.
  - On request_irq failure, call netif_device_detach() to prevent
    further traffic on the dead interface.

 drivers/net/ethernet/marvell/mvneta.c | 29 +++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index b4a845f04c05..02ea867d07a3 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -5826,6 +5826,20 @@ static int mvneta_suspend(struct device *device)
 	mvneta_stop_dev(pp);
 	rtnl_unlock();
 
+	/* Release IRQ to avoid stale MPIC mask state on resume.
+	 * On PREEMPT_RT, forced-threaded oneshot IRQs may leave the
+	 * interrupt masked (depth>0) at suspend time. This prevents
+	 * resume_device_irqs() from restoring the MPIC CPU routing,
+	 * permanently disabling the interrupt. Re-requesting the IRQ
+	 * on resume guarantees a clean state.
+	 */
+	if (pp->neta_armada3700)
+		free_irq(dev->irq, pp);
+	else {
+		on_each_cpu(mvneta_percpu_disable, pp, true);
+		free_percpu_irq(dev->irq, pp->ports);
+	}
+
 	for (queue = 0; queue < rxq_number; queue++) {
 		struct mvneta_rx_queue *rxq = &pp->rxqs[queue];
 
@@ -5892,6 +5906,21 @@ static int mvneta_resume(struct device *device)
 		mvneta_txq_hw_init(pp, txq);
 	}
 
+	/* Re-request IRQ (see comment in mvneta_suspend) */
+	if (pp->neta_armada3700) {
+		err = request_irq(dev->irq, mvneta_isr, 0, dev->name, pp);
+	} else {
+		err = request_percpu_irq(dev->irq, mvneta_percpu_isr,
+					dev->name, pp->ports);
+		if (!err)
+			on_each_cpu(mvneta_percpu_enable, pp, true);
+	}
+	if (err) {
+		netdev_err(dev, "cannot request irq %d\n", dev->irq);
+		netif_device_detach(dev);
+		return err;
+	}
+
 	if (!pp->neta_armada3700) {
 		spin_lock(&pp->lock);
 		pp->is_stopped = false;
-- 
2.43.0