HID: hid-appletb-kbd: add support for fn toggle between media and function mode

This patch adds support for the switching between the Media and Function
keys on the touchbar by pressing the Fn key on Apple Internal Keyboard.

Signed-off-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

Author: AdityaGarg8

drivers/hid/hid-appletb-kbd.c

@@ -26,6 +26,8 @@
 #define APPLETB_KBD_MODE_OFF	3
 #define APPLETB_KBD_MODE_MAX	APPLETB_KBD_MODE_OFF
 
+#define APPLETB_DEVID_KEYBOARD	1
+
 #define HID_USAGE_MODE		0x00ff0004
 
 static int appletb_tb_def_mode = APPLETB_KBD_MODE_SPCL;
@@ -35,11 +37,18 @@ MODULE_PARM_DESC(mode, "Default touchbar mode:\n"
 			 "    1 - function-keys\n"
 			 "    [2] - special keys");
 
+static bool appletb_tb_fn_toggle = true;
+module_param_named(fntoggle, appletb_tb_fn_toggle, bool, 0644);
+MODULE_PARM_DESC(fntoggle, "Switch between Fn and media controls on pressing Fn key");
+
 struct appletb_kbd {
 	struct hid_field *mode_field;
 
 	u8 saved_mode;
 	u8 current_mode;
+	struct input_handler inp_handler;
+	struct input_handle kbd_handle;
+
 };
 
 static const struct key_entry appletb_kbd_keymap[] = {
@@ -172,6 +181,75 @@ static int appletb_kbd_hid_event(struct hid_device *hdev, struct hid_field *fiel
 	return kbd->current_mode == APPLETB_KBD_MODE_OFF;
 }
 
+static void appletb_kbd_inp_event(struct input_handle *handle, unsigned int type,
+			      unsigned int code, int value)
+{
+	struct appletb_kbd *kbd = handle->private;
+
+	if (type == EV_KEY && code == KEY_FN && appletb_tb_fn_toggle) {
+		if (value == 1) {
+			kbd->saved_mode = kbd->current_mode;
+			if (kbd->current_mode == APPLETB_KBD_MODE_SPCL)
+				appletb_kbd_set_mode(kbd, APPLETB_KBD_MODE_FN);
+			else if (kbd->current_mode == APPLETB_KBD_MODE_FN)
+				appletb_kbd_set_mode(kbd, APPLETB_KBD_MODE_SPCL);
+		} else if (value == 0) {
+			if (kbd->saved_mode != kbd->current_mode)
+				appletb_kbd_set_mode(kbd, kbd->saved_mode);
+		}
+	}
+}
+
+static int appletb_kbd_inp_connect(struct input_handler *handler,
+			       struct input_dev *dev,
+			       const struct input_device_id *id)
+{
+	struct appletb_kbd *kbd = handler->private;
+	struct input_handle *handle;
+	int rc;
+
+	if (id->driver_info == APPLETB_DEVID_KEYBOARD) {
+		handle = &kbd->kbd_handle;
+		handle->name = "tbkbd";
+	} else {
+		return -ENOENT;
+	}
+
+	if (handle->dev)
+		return -EEXIST;
+
+	handle->open = 0;
+	handle->dev = input_get_device(dev);
+	handle->handler = handler;
+	handle->private = kbd;
+
+	rc = input_register_handle(handle);
+	if (rc)
+		goto err_free_dev;
+
+	rc = input_open_device(handle);
+	if (rc)
+		goto err_unregister_handle;
+
+	return 0;
+
+ err_unregister_handle:
+	input_unregister_handle(handle);
+ err_free_dev:
+	input_put_device(handle->dev);
+	handle->dev = NULL;
+	return rc;
+}
+
+static void appletb_kbd_inp_disconnect(struct input_handle *handle)
+{
+	input_close_device(handle);
+	input_unregister_handle(handle);
+
+	input_put_device(handle->dev);
+	handle->dev = NULL;
+}
+
 static int appletb_kbd_input_configured(struct hid_device *hdev, struct hid_input *hidinput)
 {
 	int idx;
@@ -195,6 +273,40 @@ static int appletb_kbd_input_configured(struct hid_device *hdev, struct hid_inpu
 	return 0;
 }
 
+static const struct input_device_id appletb_kbd_input_devices[] = {
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_BUS |
+			INPUT_DEVICE_ID_MATCH_VENDOR |
+			INPUT_DEVICE_ID_MATCH_KEYBIT,
+		.bustype = BUS_USB,
+		.vendor = USB_VENDOR_ID_APPLE,
+		.keybit = { [BIT_WORD(KEY_FN)] = BIT_MASK(KEY_FN) },
+		.driver_info = APPLETB_DEVID_KEYBOARD,
+	},
+	{ }
+};
+
+static bool appletb_kbd_match_internal_device(struct input_handler *handler,
+					  struct input_dev *inp_dev)
+{
+	struct device *dev = &inp_dev->dev;
+
+	/* in kernel: dev && !is_usb_device(dev) */
+	while (dev && !(dev->type && dev->type->name &&
+			!strcmp(dev->type->name, "usb_device")))
+		dev = dev->parent;
+
+	/*
+	 * Apple labels all their internal keyboards and trackpads as such,
+	 * instead of maintaining an ever expanding list of product-id's we
+	 * just look at the device's product name.
+	 */
+	if (dev)
+		return !!strstr(to_usb_device(dev)->product, "Internal Keyboard");
+
+	return false;
+}
+
 static int appletb_kbd_probe(struct hid_device *hdev, const struct hid_device_id *id)
 {
 	struct appletb_kbd *kbd;
@@ -227,6 +339,20 @@ static int appletb_kbd_probe(struct hid_device *hdev, const struct hid_device_id
 		goto stop_hw;
 	}
 
+	kbd->inp_handler.event = appletb_kbd_inp_event;
+	kbd->inp_handler.connect = appletb_kbd_inp_connect;
+	kbd->inp_handler.disconnect = appletb_kbd_inp_disconnect;
+	kbd->inp_handler.name = "appletb";
+	kbd->inp_handler.id_table = appletb_kbd_input_devices;
+	kbd->inp_handler.match = appletb_kbd_match_internal_device;
+	kbd->inp_handler.private = kbd;
+
+	ret = input_register_handler(&kbd->inp_handler);
+	if (ret) {
+		dev_err_probe(dev, ret, "Unable to register keyboard handler\n");
+		goto close_hw;
+	}
+
 	ret = appletb_kbd_set_mode(kbd, appletb_tb_def_mode);
 	if (ret) {
 		dev_err_probe(dev, ret, "Failed to set touchbar mode\n");
@@ -250,6 +376,8 @@ static void appletb_kbd_remove(struct hid_device *hdev)
 
 	appletb_kbd_set_mode(kbd, APPLETB_KBD_MODE_OFF);
 
+	input_unregister_handler(&kbd->inp_handler);
+
 	hid_hw_close(hdev);
 	hid_hw_stop(hdev);
 }