Jiri Kosina [off-list ref] 於 2021年1月7日 週四 下午5:23寫道：

On Wed, 23 Dec 2020, Jian-Hong Pan wrote:

quoted

Some Chicony's keyboards support airplane mode hotkey (Fn+F2) with
"Wireless Radio Control" feature. For example, the wireless keyboard
[04f2:1236] shipped with ASUS all-in-one desktop.

After consulting Chicony for this hotkey, learned the device will send
with 0x11 as the report ID and 0x1 as the value when the key is pressed
down.

This patch maps the event as KEY_RFKILL.

I don't know how exactly does the report descriptor of that device look
like, but is this not doable from userspace via setkeycode() (udev/systemd
is shipping a lot of such mappings already -- see evdev/keyboard
definitions in hwdb).

Thanks for your suggestion!

I have tested the key with evtest.  But it has no response from all
inputs.  Nor response from xev.

So, I tried usb monitor to see what does it send:

$ lsusb -d 04f2:1236
Bus 001 Device 002: ID 04f2:1236 Chicony Electronics Co., Ltd
$ sudo modprobe usbmon
$ sudo cat /sys/kernel/debug/usb/usbmon/1u
ffff9145e0dea6c0 348311963 C Ii:1:002:1 0:8 8 = 00000000 00000000
ffff9145e0dea6c0 348311996 S Ii:1:002:1 -115:8 8 <
ffff9145e0deaf00 352852533 C Ii:1:002:2 0:4 2 = 1101
ffff9145e0deaf00 352852547 S Ii:1:002:2 -115:4 3 <

It sends 0x1101 for the hotkey.  The same response from hid events:

$ sudo cat /sys/kernel/debug/hid/0003\:04F2\:1236.0002/events
report (size 2) (numbered) =  11 01

Then, I notice there is the RFKILL event listed on the "Chicony USB
Receiver Wireless Radio Control" device:

$ sudo evtest /dev/input/event8
Input driver version is 1.0.1
Input device ID: bus 0x3 vendor 0x4f2 product 0x1236 version 0x111
Input device name: "Chicony USB Receiver Wireless Radio Control"
Supported events:
  Event type 0 (EV_SYN)
  Event type 1 (EV_KEY)
    Event code 103 (KEY_UP)
    Event code 105 (KEY_LEFT)
    Event code 106 (KEY_RIGHT)
    Event code 108 (KEY_DOWN)
    Event code 116 (KEY_POWER)
    Event code 138 (KEY_HELP)
    Event code 139 (KEY_MENU)
    Event code 142 (KEY_SLEEP)
    Event code 143 (KEY_WAKEUP)
    Event code 148 (KEY_PROG1)
    Event code 174 (KEY_EXIT)
    Event code 227 (KEY_SWITCHVIDEOMODE)
    Event code 247 (KEY_RFKILL)
    Event code 314 (BTN_SELECT)
    Event code 315 (BTN_START)
    Event code 353 (KEY_SELECT)
    Event code 356 (KEY_POWER2)
    Event code 408 (KEY_RESTART)
    Event code 438 (KEY_CONTEXT_MENU)
  Event type 2 (EV_REL)
    Event code 9 (REL_MISC)
  Event type 3 (EV_ABS)
...

Also, after debugging, I found its HID application ID is
HID_GD_WIRELESS_RADIO_CTLS 0x0001000c [1].
Then, I searched HID_GD_WIRELESS_RADIO_CTLS in the kernel.  I found
HID_GD_RFKILL_BTN [2] is mapped in hid-input.
However, this key press on the Chicony keyboard maps to nothing, nor
HID_GD_RFKILL_BTN.  Only have the HID report with raw data 0x11 0x00
as mentioned above.
It is more like ignored by the kernel and it even has no scancode.
That's why I try to map it as KEY_RFKILL in the driver.

[1] https://elixir.bootlin.com/linux/v5.10/source/include/linux/hid.h#L181
[2] https://elixir.bootlin.com/linux/v5.10/source/drivers/hid/hid-input.c#L743

Regards,
Jian-Hong Pan