powerpc/pseries: start rtasd before PCI probing

A strange behaviour is observed when comparing PCI hotplug in QEMU, between
x86 and pseries. If you consider the following steps:
- start a VM
- add a PCI device via the QEMU monitor before the rtasd has started (for
  example starting the VM in paused state, or hotplug during FW or boot
  loader)
- resume the VM execution

The x86 kernel detects the PCI device, but the pseries one does not.

This happens because the rtasd kernel worker is currently started under
device_initcall, while PCI probing happens earlier under subsys_initcall.

As a consequence, if we have a pending RTAS event at boot time, a message
is printed and the event is dropped.

This patch moves all the initialization of rtasd to arch_initcall, which is
run before subsys_call: this way, logging_enabled is true when the RTAS
event pops up and it is not lost anymore.

The proc fs bits stay at device_initcall because they cannot be run before
fs_initcall.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/rtasd.c

@@ -526,10 +526,8 @@ void rtas_cancel_event_scan(void)
 }
 EXPORT_SYMBOL_GPL(rtas_cancel_event_scan);
 
-static int __init rtas_init(void)
+static int __init rtas_event_scan_init(void)
 {
-	struct proc_dir_entry *entry;
-
 	if (!machine_is(pseries) && !machine_is(chrp))
 		return 0;
 
@@ -562,13 +560,27 @@ static int __init rtas_init(void)
 		return -ENOMEM;
 	}
 
+	start_event_scan();
+
+	return 0;
+}
+arch_initcall(rtas_event_scan_init);
+
+static int __init rtas_init(void)
+{
+	struct proc_dir_entry *entry;
+
+	if (!machine_is(pseries) && !machine_is(chrp))
+		return 0;
+
+	if (!rtas_log_buf)
+		return -ENODEV;
+
 	entry = proc_create("powerpc/rtas/error_log", S_IRUSR, NULL,
 			    &proc_rtas_log_operations);
 	if (!entry)
 		printk(KERN_ERR "Failed to create error_log proc entry\n");
 
-	start_event_scan();
-
 	return 0;
 }
 __initcall(rtas_init);