parisc: Allow to reboot machine after system halt

In case a machine can't power-off itself on system shutdown,
allow the user to reboot it by pressing the RETURN key.

Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/kernel/process.c

@@ -122,13 +122,18 @@ void machine_power_off(void)
 	/* It seems we have no way to power the system off via
 	 * software. The user has to press the button himself. */
 
-	printk(KERN_EMERG "System shut down completed.\n"
-	       "Please power this system off now.");
+	printk("Power off or press RETURN to reboot.\n");
 
 	/* prevent soft lockup/stalled CPU messages for endless loop. */
 	rcu_sysrq_start();
 	lockup_detector_soft_poweroff();
-	for (;;);
+	while (1) {
+		/* reboot if user presses RETURN key */
+		if (pdc_iodc_getc() == 13) {
+			printk("Rebooting...\n");
+			machine_restart(NULL);
+		}
+	}
 }
 
 void (*pm_power_off)(void);