net: ag71xx: disable napi interrupts during probe

ag71xx_probe is registering ag71xx_interrupt as handler for gmac0/gmac1
interrupts. The handler is trying to use napi_schedule to handle the
processing of packets. But the netif_napi_add for this device is
called a lot later in ag71xx_probe.

It can therefore happen that a still running gmac0/gmac1 is triggering the
interrupt handler with a bit from AG71XX_INT_POLL set in
AG71XX_REG_INT_STATUS. The handler will then call napi_schedule and the
napi code will crash the system because the ag->napi is not yet
initialized.

The gmcc0/gmac1 must be brought in a state in which it doesn't signal a
AG71XX_INT_POLL related status bits as interrupt before registering the
interrupt handler. ag71xx_hw_start will take care of re-initializing the
AG71XX_REG_INT_ENABLE.

This will become relevant when dual GMAC devices get added here.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://patch.msgid.link/20240905194938.8453-8-rosenp@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/atheros/ag71xx.c

@@ -1850,6 +1850,12 @@ static int ag71xx_probe(struct platform_device *pdev)
 	if (!ag->mac_base)
 		return -ENOMEM;
 
+	/* ensure that HW is in manual polling mode before interrupts are
+	 * activated. Otherwise ag71xx_interrupt might call napi_schedule
+	 * before it is initialized by netif_napi_add.
+	 */
+	ag71xx_int_disable(ag, AG71XX_INT_POLL);
+
 	ndev->irq = platform_get_irq(pdev, 0);
 	err = devm_request_irq(&pdev->dev, ndev->irq, ag71xx_interrupt,
 			       0x0, dev_name(&pdev->dev), ndev);