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Add HID driver to filter BTN_0 (FN key) events on Surface devices - #1870
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Fixes linux-surface#1851 - FN key causing focus to get stuck in KWin Wayland The Surface Aggregator Module firmware incorrectly reports the FN key as BTN_0 (button 256). This can get stuck in pressed state, flooding the input system and breaking focus tracking in compositors. This patch adds a new HID driver (hid-surface.c) that filters BTN_0 events while allowing all other keyboard/touchpad functionality to work normally. Tested on Surface Laptop 4 AMD with KDE Plasma Wayland.
The fix also applies to kernel 6.17.1 - tested and confirmed bug exists there too.
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Added to our kernel repo in linux-surface/kernel@7dcd050. |
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Summary
Fixes #1851 - FN key causing focus to get stuck in KWin Wayland
The Surface Aggregator Module firmware incorrectly reports the FN key as BTN_0 (button 256) through runtime HID events. This button can get stuck in pressed state, flooding the input system (~29 events per second), which breaks focus tracking in KWin Wayland compositor.
Solution
This PR adds kernel patches for 6.16 and 6.17 that create a HID driver (
hid-surface.c) to filter BTN_0 events using theeventcallback. This prevents BTN_0 from reaching the input subsystem while allowing all other keyboard/touchpad functionality to work normally.Testing Results
Hardware: Surface Laptop 4 AMD (Ryzen 5)
OS: Arch Linux
Desktop: KDE Plasma 6.4.5 Wayland
Tested on Kernel 6.16.9-arch1-1-surface
Tested on Kernel 6.17.1-arch1-1-surface
Technical Details
Key insight: BTN_0 is NOT in the HID descriptor - it's generated dynamically at runtime from HID reports. This is why the fix required using the
eventcallback rather thaninput_mapping.Why it affects KWin Wayland specifically: X11 and GNOME Wayland handle stuck button events more gracefully. KWin Wayland's focus tracking is more sensitive to input flooding.
Compatibility & Testing Request
Confirmed working:
Needs testing:
Please test if you have an Intel-based Surface device! We need to verify:
Patch Details
The patch adds 3 files totaling 99 lines per kernel version:
drivers/hid/hid-surface.c(new, 90 lines)drivers/hid/Kconfig(modified, +8 lines)drivers/hid/Makefile(modified, +1 line)Patches included for:
patches/6.16/0016-hid-surface-fn-key.patchpatches/6.17/0016-hid-surface-fn-key.patchFixes: #1851