[PATCH v4] net: mvneta: re-enable percpu interrupt on resume

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

On Marvell MPIC platforms (Armada 370/XP/38x), mvneta uses a percpu
IRQ disable/enable scheme for NAPI: the ISR (mvneta_percpu_isr) calls
disable_percpu_irq() to mask the MPIC per-CPU interrupt and schedules
NAPI poll, which calls enable_percpu_irq() on completion to unmask.

If suspend occurs while NAPI poll is pending (between
disable_percpu_irq in the ISR and enable_percpu_irq in poll
completion), the interrupt is never re-enabled:

  1. mvneta_percpu_isr: disable_percpu_irq() + napi_schedule()
     => MPIC masked, percpu_enabled cpumask bit cleared
  2. NAPI poll does not complete before suspend proceeds
     (on PREEMPT_RT this is highly likely since softirqs run in
     ksoftirqd which gets frozen; on non-RT it can happen when
     softirq processing is deferred to ksoftirqd)
  3. mvneta_stop_dev => napi_disable(): cancels the pending poll
     without executing the completion path
  4. suspend_device_irqs => IRQCHIP_MASK_ON_SUSPEND: masks MPIC
     (already masked, but records IRQS_SUSPENDED)
  5. Resume: mpic_resume checks irq_percpu_is_enabled() => false
     (bit was cleared in step 1) => skips unmask
  6. mvneta_start_dev only restores device-level INTR_NEW_MASK,
     does not touch the MPIC per-CPU mask

Result: MPIC per-CPU interrupt stays masked permanently. The NIC
generates interrupts (INTR_NEW_CAUSE != 0) but the CPU never
receives them, causing complete loss of network connectivity.

Fix by calling on_each_cpu(mvneta_percpu_enable) in the resume path
to unconditionally unmask the MPIC per-CPU interrupt regardless of
pre-suspend state.

Fixes: 12bb03b436da ("net: mvneta: Handle per-cpu interrupts")
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
---
v4:
  - Rewrite commit message with accurate root cause analysis.

v3:
  - Dropped the free_irq/request_irq approach (incorrect root cause).
  - Instead, call on_each_cpu(mvneta_percpu_enable) in the resume path
    to ensure the MPIC percpu IRQ is unmasked, matching mvneta_open().
  - Updated commit message with correct root cause analysis.

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 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 488f2663ad2c..543e566425c1 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -5918,6 +5918,9 @@ static int mvneta_resume(struct device *device)
 	rtnl_unlock();
 	mvneta_set_rx_mode(dev);
 
+	if (!pp->neta_armada3700)
+		on_each_cpu(mvneta_percpu_enable, pp, true);
+
 	return 0;
 }
 #endif
-- 
2.43.0