tty/hvc: Use IRQF_SHARED for OPAL hvc consoles

Commit 2def86a720 ("hvc: Convert to using interrupts instead of opal
events") enabled the use of interrupts in the hvc_driver for OPAL
platforms. However on machines with more than one hvc console, any
console after the first will fail to register an interrupt handler in
notifier_add_irq() since all consoles share the same IRQ number but do
not set the IRQF_SHARED flag:

  genirq: Flags mismatch irq 31. 00000000 (hvc_console) vs. 00000000 (hvc_console)
  hvc_open: request_irq failed with rc -16.

This error propagates up to hvc_open() and the console is closed, but
OPAL will still generate interrupts that are not handled, leading to
rcu_sched stall warnings.

Set IRQF_SHARED when calling request_irq(), allowing additional consoles
to start properly. This is only set for consoles handled by
hvc_opal_probe(), leaving other types unaffected.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/tty/hvc/hvc_opal.c

@@ -224,6 +224,9 @@ static int hvc_opal_probe(struct platform_device *dev)
 	hp = hvc_alloc(termno, irq, ops, MAX_VIO_PUT_CHARS);
 	if (IS_ERR(hp))
 		return PTR_ERR(hp);
+
+	/* hvc consoles on powernv may need to share a single irq */
+	hp->flags = IRQF_SHARED;
 	dev_set_drvdata(&dev->dev, hp);
 
 	return 0;