Toshiba P755 S5387 Keyboard backlight won't toggle status

Question

Toshiba P755 S5387 Keyboard backlight won't toggle status through function key (FN+Z) or multimedia key (that square with an arrow inside) on Ubuntu 22.04.

FN key is recognized and a status box is displayed on Gnome, but status is not changed. Multimedia key does nothing.

Only changing backlight status on BIOS works.

Tried several workarounds, none worked:

• brightnessctl, xset, gdbus (https://wiki.archlinux.org/title/keyboard_backlight)
• echo {0-1} | sudo tee /sys/class/leds/toshiba::kbd_backlight/brightness (How to make my Toshiba u940 laptop's keyboard backlit to work?)
• acpi_backlight=vendor acpi_osi=linux on grub

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Plus: If your backlight simply do not works, no matter how BIOS status was configured, there is a workaround, see comment 108 here: https://bugzilla.kernel.org/show_bug.cgi?id=32742#c108

Just start on Windows: start a Windows install media (or dual boot, no matter) and reboot (maybe also necessary to tap on backlight multimedia key, can't confirm this). It's restore something and backlight starts to work.

Answer 1

See comments 112 and 113 here: https://bugzilla.kernel.org/show_bug.cgi?id=32742#c112

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$ echo ${mode} > /sys/devices/LNXSYSTM:00/LNXSYBUS:00/TOS1900:00/kbd_backlight_mode

Where mode can be:

• 2 = timer
• 8 = on
• 16 = off

Obs.: TOS1900 can be TOS6208 or other value. Don't know what changes this.

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You can bind a script to a custom keyboard shortcut and map FN+Z. Reboot needed.

Here a sample script:

#!/bin/bash
backlight_mode_file='/sys/devices/LNXSYSTM:00/LNXSYBUS:00/TOS1900:00/kbd_backlight_mode'
kbd_state=$(<${backlight_mode_file})
if [[ "$kbd_state" -eq "16" ]]; then
    echo 8 > ${backlight_mode_file}
elif [[ "$kbd_state" -eq "8" ]]; then
    echo 2 > ${backlight_mode_file}
elif [[ "$kbd_state" -eq "2" ]]; then
    echo 16 > ${backlight_mode_file}
fi

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Note that besides this workaround is functional, screen status notification icon partially works, it appears sometimes but don't change icon. In my case it is shown only when backlight is changed to OFF, maybe because brightnessctl --device='toshiba::kbd_backlight' info returns 0.