dell-rbtn: Export notifier for other kernel modules

This patch exports notifier functions so other modules can receive HW
switch events. By default when some module register notifier, dell-rbtn
driver automatically remove rfkill interfaces from system (it is expected
that other module will use events for other rfkill interface). This
behaviour can be changed with new module parameter "auto_remove_rfkill".

This patch is designed for dell-laptop module for receiving those events.
Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
[dvhart@linux.intel.com: Cleanup MODULE_PARM_DESC formatting and grammar]
Signed-off-by: Darren Hart <dvhart@linux.intel.com>

drivers/platform/x86/dell-rbtn.c

@@ -232,6 +232,86 @@ static struct acpi_driver rbtn_driver = {
 };
 
 
+/*
+ * notifier export functions
+ */
+
+static bool auto_remove_rfkill = true;
+
+static ATOMIC_NOTIFIER_HEAD(rbtn_chain_head);
+
+static int rbtn_inc_count(struct device *dev, void *data)
+{
+	struct acpi_device *device = to_acpi_device(dev);
+	struct rbtn_data *rbtn_data = device->driver_data;
+	int *count = data;
+
+	if (rbtn_data->type == RBTN_SLIDER)
+		(*count)++;
+
+	return 0;
+}
+
+static int rbtn_switch_dev(struct device *dev, void *data)
+{
+	struct acpi_device *device = to_acpi_device(dev);
+	struct rbtn_data *rbtn_data = device->driver_data;
+	bool enable = data;
+
+	if (rbtn_data->type != RBTN_SLIDER)
+		return 0;
+
+	if (enable)
+		rbtn_rfkill_init(device);
+	else
+		rbtn_rfkill_exit(device);
+
+	return 0;
+}
+
+int dell_rbtn_notifier_register(struct notifier_block *nb)
+{
+	bool first;
+	int count;
+	int ret;
+
+	count = 0;
+	ret = driver_for_each_device(&rbtn_driver.drv, NULL, &count,
+				     rbtn_inc_count);
+	if (ret || count == 0)
+		return -ENODEV;
+
+	first = !rbtn_chain_head.head;
+
+	ret = atomic_notifier_chain_register(&rbtn_chain_head, nb);
+	if (ret != 0)
+		return ret;
+
+	if (auto_remove_rfkill && first)
+		ret = driver_for_each_device(&rbtn_driver.drv, NULL,
+					     (void *)false, rbtn_switch_dev);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dell_rbtn_notifier_register);
+
+int dell_rbtn_notifier_unregister(struct notifier_block *nb)
+{
+	int ret;
+
+	ret = atomic_notifier_chain_unregister(&rbtn_chain_head, nb);
+	if (ret != 0)
+		return ret;
+
+	if (auto_remove_rfkill && !rbtn_chain_head.head)
+		ret = driver_for_each_device(&rbtn_driver.drv, NULL,
+					     (void *)true, rbtn_switch_dev);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dell_rbtn_notifier_unregister);
+
+
 /*
  * acpi driver functions
  */
@@ -266,6 +346,9 @@ static int rbtn_add(struct acpi_device *device)
 		ret = rbtn_input_init(rbtn_data);
 		break;
 	case RBTN_SLIDER:
+		if (auto_remove_rfkill && rbtn_chain_head.head)
+			ret = 0;
+		else
 			ret = rbtn_rfkill_init(device);
 		break;
 	default:
@@ -313,6 +396,7 @@ static void rbtn_notify(struct acpi_device *device, u32 event)
 		break;
 	case RBTN_SLIDER:
 		rbtn_rfkill_event(device);
+		atomic_notifier_call_chain(&rbtn_chain_head, event, device);
 		break;
 	default:
 		break;
@@ -326,6 +410,13 @@ static void rbtn_notify(struct acpi_device *device, u32 event)
 
 module_acpi_driver(rbtn_driver);
 
+module_param(auto_remove_rfkill, bool, 0444);
+
+MODULE_PARM_DESC(auto_remove_rfkill, "Automatically remove rfkill devices when "
+				     "other modules start receiving events "
+				     "from this module and re-add them when "
+				     "the last module stops receiving events "
+				     "(default true)");
 MODULE_DEVICE_TABLE(acpi, rbtn_ids);
 MODULE_DESCRIPTION("Dell Airplane Mode Switch driver");
 MODULE_AUTHOR("Pali Rohár <pali.rohar@gmail.com>");

drivers/platform/x86/dell-rbtn.h

+/*
+    Dell Airplane Mode Switch driver
+    Copyright (C) 2014-2015  Pali Rohár <pali.rohar@gmail.com>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+*/
+
+#ifndef _DELL_RBTN_H_
+#define _DELL_RBTN_H_
+
+struct notifier_block;
+
+int dell_rbtn_notifier_register(struct notifier_block *nb);
+int dell_rbtn_notifier_unregister(struct notifier_block *nb);
+
+#endif