eeepc-wmi: serialize access to wmi method

\AMW0.WMBC, which is the main method that we use,
is not reentrant. When wireless hotpluging is enabled,
toggling the status of the wireless device using WMBC will
trigger a notification and the notification handler need to
call WMBC again to get the new status of the device, this
will trigger the following error:

ACPI Error (dswload-0802): [_T_0] Namespace lookup failure, AE_ALREADY_EXISTS
ACPI Exception: AE_ALREADY_EXISTS, During name lookup/catalog (20100428/psloop-231)
ACPI Error (psparse-0537): Method parse/execution failed [\AMW0.WMBC] (Node f7023b88), AE_ALREADY_EXISTS
ACPI: Marking method WMBC as Serialized because of AE_ALREADY_EXISTS error

Since there is currently no way to tell the acpi subsystem to mark
a method as serialized, we do it in eeepc-wmi.

Of course, we could let the first call fail, and then it would work,
but it doesn't seems really clean, and it will make the first
WMBC call return a random value.

This patch was tested on EeePc 1000H with a RaLink RT2860
wireless card using the rt2800pci driver. rt2860sta driver
seems to deadlock when we remove the pci device...
Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/eeepc-wmi.c

@@ -137,6 +137,9 @@ struct eeepc_wmi {
 
 	struct hotplug_slot *hotplug_slot;
 	struct mutex hotplug_lock;
+	struct mutex wmi_lock;
+	struct workqueue_struct *hotplug_workqueue;
+	struct work_struct hotplug_work;
 
 	struct eeepc_wmi_debug debug;
 };
@@ -370,15 +373,19 @@ static void eeepc_rfkill_hotplug(struct eeepc_wmi *eeepc)
 {
 	struct pci_dev *dev;
 	struct pci_bus *bus;
-	bool blocked = eeepc_wlan_rfkill_blocked(eeepc);
+	bool blocked;
 	bool absent;
 	u32 l;
 
-	if (eeepc->wlan_rfkill)
-		rfkill_set_sw_state(eeepc->wlan_rfkill, blocked);
+	mutex_lock(&eeepc->wmi_lock);
+	blocked = eeepc_wlan_rfkill_blocked(eeepc);
+	mutex_unlock(&eeepc->wmi_lock);
 
 	mutex_lock(&eeepc->hotplug_lock);
 
+	if (eeepc->wlan_rfkill)
+		rfkill_set_sw_state(eeepc->wlan_rfkill, blocked);
+
 	if (eeepc->hotplug_slot) {
 		bus = pci_find_bus(0, 1);
 		if (!bus) {
@@ -435,7 +442,14 @@ static void eeepc_rfkill_notify(acpi_handle handle, u32 event, void *data)
 	if (event != ACPI_NOTIFY_BUS_CHECK)
 		return;
 
-	eeepc_rfkill_hotplug(eeepc);
+	/*
+	 * We can't call directly eeepc_rfkill_hotplug because most
+	 * of the time WMBC is still being executed and not reetrant.
+	 * There is currently no way to tell ACPICA that  we want this
+	 * method to be serialized, we schedule a eeepc_rfkill_hotplug
+	 * call later, in a safer context.
+	 */
+	queue_work(eeepc->hotplug_workqueue, &eeepc->hotplug_work);
 }
 
 static int eeepc_register_rfkill_notifier(struct eeepc_wmi *eeepc,
@@ -508,6 +522,14 @@ static struct hotplug_slot_ops eeepc_hotplug_slot_ops = {
 	.get_power_status = eeepc_get_adapter_status,
 };
 
+static void eeepc_hotplug_work(struct work_struct *work)
+{
+	struct eeepc_wmi *eeepc;
+
+	eeepc = container_of(work, struct eeepc_wmi, hotplug_work);
+	eeepc_rfkill_hotplug(eeepc);
+}
+
 static int eeepc_setup_pci_hotplug(struct eeepc_wmi *eeepc)
 {
 	int ret = -ENOMEM;
@@ -518,6 +540,13 @@ static int eeepc_setup_pci_hotplug(struct eeepc_wmi *eeepc)
 		return -ENODEV;
 	}
 
+	eeepc->hotplug_workqueue =
+		create_singlethread_workqueue("hotplug_workqueue");
+	if (!eeepc->hotplug_workqueue)
+		goto error_workqueue;
+
+	INIT_WORK(&eeepc->hotplug_work, eeepc_hotplug_work);
+
 	eeepc->hotplug_slot = kzalloc(sizeof(struct hotplug_slot), GFP_KERNEL);
 	if (!eeepc->hotplug_slot)
 		goto error_slot;
@@ -547,6 +576,8 @@ static int eeepc_setup_pci_hotplug(struct eeepc_wmi *eeepc)
 	kfree(eeepc->hotplug_slot);
 	eeepc->hotplug_slot = NULL;
 error_slot:
+	destroy_workqueue(eeepc->hotplug_workqueue);
+error_workqueue:
 	return ret;
 }
 
@@ -575,6 +606,34 @@ static void eeepc_rfkill_query(struct rfkill *rfkill, void *data)
 	rfkill_set_sw_state(rfkill, !(retval & 0x1));
 }
 
+static int eeepc_rfkill_wlan_set(void *data, bool blocked)
+{
+	struct eeepc_wmi *eeepc = data;
+	int ret;
+
+	/*
+	 * This handler is enabled only if hotplug is enabled.
+	 * In this case, the eeepc_wmi_set_devstate() will
+	 * trigger a wmi notification and we need to wait
+	 * this call to finish before being able to call
+	 * any wmi method
+	 */
+	mutex_lock(&eeepc->wmi_lock);
+	ret = eeepc_rfkill_set((void *)(long)EEEPC_WMI_DEVID_WLAN, blocked);
+	mutex_unlock(&eeepc->wmi_lock);
+	return ret;
+}
+
+static void eeepc_rfkill_wlan_query(struct rfkill *rfkill, void *data)
+{
+	eeepc_rfkill_query(rfkill, (void *)(long)EEEPC_WMI_DEVID_WLAN);
+}
+
+static const struct rfkill_ops eeepc_rfkill_wlan_ops = {
+	.set_block = eeepc_rfkill_wlan_set,
+	.query = eeepc_rfkill_wlan_query,
+};
+
 static const struct rfkill_ops eeepc_rfkill_ops = {
 	.set_block = eeepc_rfkill_set,
 	.query = eeepc_rfkill_query,
@@ -603,6 +662,10 @@ static int eeepc_new_rfkill(struct eeepc_wmi *eeepc,
 	if (!retval || retval == 0x00060000)
 		return -ENODEV;
 
+	if (dev_id == EEEPC_WMI_DEVID_WLAN && eeepc->hotplug_wireless)
+		*rfkill = rfkill_alloc(name, &eeepc->platform_device->dev, type,
+				       &eeepc_rfkill_wlan_ops, eeepc);
+	else
 		*rfkill = rfkill_alloc(name, &eeepc->platform_device->dev, type,
 				       &eeepc_rfkill_ops, (void *)(long)dev_id);
 
@@ -636,6 +699,8 @@ static void eeepc_wmi_rfkill_exit(struct eeepc_wmi *eeepc)
 	eeepc_rfkill_hotplug(eeepc);
 	if (eeepc->hotplug_slot)
 		pci_hp_deregister(eeepc->hotplug_slot);
+	if (eeepc->hotplug_workqueue)
+		destroy_workqueue(eeepc->hotplug_workqueue);
 
 	if (eeepc->bluetooth_rfkill) {
 		rfkill_unregister(eeepc->bluetooth_rfkill);
@@ -654,6 +719,7 @@ static int eeepc_wmi_rfkill_init(struct eeepc_wmi *eeepc)
 	int result = 0;
 
 	mutex_init(&eeepc->hotplug_lock);
+	mutex_init(&eeepc->wmi_lock);
 
 	result = eeepc_new_rfkill(eeepc, &eeepc->wlan_rfkill,
 				  "eeepc-wlan", RFKILL_TYPE_WLAN,