Re: [PATCH v3 4/6] USB: core: Add wireless_status sysfs attribute

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Mar 02, 2023 at 11:55:53AM +0100, Bastien Nocera wrote:
> 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>
> ---
> Updated commit message and documentation in v2 so that the commit
> doesn't need to reference older discussions.
> 
> Trimmed the width of the sysfs docs in v3.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>