USB: core: Add wireless_status sysfs attribute

Add a wireless_status sysfs attribute to USB devices to keep track of
whether a USB device that's comprised of a receiver dongle and an emitter
device over a, most of the time proprietary, wireless link has its emitter
connected or disconnected.

This will be used by user-space OS components to determine whether the
battery-powered part of the device is wirelessly connected or not,
allowing, for example:
- upower to hide the battery for devices where the device is turned off
  but the receiver plugged in, rather than showing 0%, or other values
  that could be confusing to users
- Pipewire to hide a headset from the list of possible inputs or outputs
  or route audio appropriately if the headset is suddenly turned off, or
  turned on
- libinput to determine whether a keyboard or mouse is present when its
  receiver is plugged in.

This is done at the USB interface level as:
- the interface on which the wireless status is detected is sometimes
  not the same as where it could be consumed (eg. the audio interface
  on a headset dongle will still appear even if the headset is turned
  off), and we cannot have synchronisation of status across subsystems.
- this behaviour is not specific to HID devices, even if the protocols
  used to determine whether or not the remote device is connected can
  be HID.

This is not an attribute that is meant to replace protocol specific
APIs, such as the ones available for WWAN, WLAN/Wi-Fi, or Bluetooth
or any other sort of networking, but solely for wireless devices with
an ad-hoc “lose it and your device is e-waste” receiver dongle.

The USB interface will only be exporting the wireless_status sysfs
attribute if it gets set through the API exported in the next commit.

Signed-off-by: Bastien Nocera <hadess@hadess.net>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20230302105555.51417-4-hadess@hadess.net
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/usb/core/usb.h b/drivers/usb/core/usb.h
index 0eac7d4285d1..3f14e15f07f6 100644
--- a/drivers/usb/core/usb.h
+++ b/drivers/usb/core/usb.h
@@ -15,6 +15,7 @@ extern int usb_create_sysfs_dev_files(struct usb_device *dev);
 extern void usb_remove_sysfs_dev_files(struct usb_device *dev);
 extern void usb_create_sysfs_intf_files(struct usb_interface *intf);
 extern void usb_remove_sysfs_intf_files(struct usb_interface *intf);
+extern int usb_update_wireless_status_attr(struct usb_interface *intf);
 extern int usb_create_ep_devs(struct device *parent,
 				struct usb_host_endpoint *endpoint,
 				struct usb_device *udev);