ACPI: EC: Limit explicit removal of query handlers to custom query handlers

According to the ACPI spec part 5.6.4.1.2, EC query handlers discovered
thru ACPI should not be removed when a driver removes his custom query
handler. On the Acer Travelmate 4002WLMi for example, such a query
handler is used as a fallback to handle the EC SMBus alert when no driver
is present.
Change acpi_ec_remove_query_handlers() so that only custom query
handlers are removed then remove_all is false. Query handlers discovered
thru ACPI will still get removed when remove_all is true, which happens
on device removal. Also add a simple check to ensure that
acpi_ec_add_query_handler() is always called with either handle or func
being set, since custom query handlers are detected based whether
handlers->func is set or not.

Tested on a Acer Travelmate 4002WLMi.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
[ rjw: Comment adjustment ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/ec.c

@@ -1083,9 +1083,12 @@ int acpi_ec_add_query_handler(struct acpi_ec *ec, u8 query_bit,
 			      acpi_handle handle, acpi_ec_query_func func,
 			      void *data)
 {
-	struct acpi_ec_query_handler *handler =
-	    kzalloc(sizeof(struct acpi_ec_query_handler), GFP_KERNEL);
+	struct acpi_ec_query_handler *handler;
 
+	if (!handle && !func)
+		return -EINVAL;
+
+	handler = kzalloc(sizeof(*handler), GFP_KERNEL);
 	if (!handler)
 		return -ENOMEM;
 
@@ -1097,6 +1100,7 @@ int acpi_ec_add_query_handler(struct acpi_ec *ec, u8 query_bit,
 	kref_init(&handler->kref);
 	list_add(&handler->node, &ec->list);
 	mutex_unlock(&ec->mutex);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(acpi_ec_add_query_handler);
@@ -1109,9 +1113,16 @@ static void acpi_ec_remove_query_handlers(struct acpi_ec *ec,
 
 	mutex_lock(&ec->mutex);
 	list_for_each_entry_safe(handler, tmp, &ec->list, node) {
-		if (remove_all || query_bit == handler->query_bit) {
+		/*
+		 * When remove_all is false, only remove custom query handlers
+		 * which have handler->func set. This is done to preserve query
+		 * handlers discovered thru ACPI, as they should continue handling
+		 * EC queries.
+		 */
+		if (remove_all || (handler->func && handler->query_bit == query_bit)) {
 			list_del_init(&handler->node);
 			list_add(&handler->node, &free_list);
+
 		}
 	}
 	mutex_unlock(&ec->mutex);