bug#81532: Lack of software debouncing / polling rate limit causes interrupt lockup in CSM/BIOS mode on AMD B550

tag 81532 notabug
close 81523
stop

closing here as grub is not part of GNU coreutils.

I suggest you resend to <[email protected]>

cheers,
Padraig

On 01/08/2026 10:05, GC via GNU coreutils Bug Reports wrote:
> 
> Subject: Bug: Lack of software debouncing / polling rate limit causes
> interrupt lockup in CSM/BIOS mode on AMD B550
> 
> 
> 
> Hello GRUB Developers,
> 
> I am reporting a severe input issue when running GRUB2 in legacy
> BIOS/CSM mode on certain AMD B550 platforms (specifically the MSI MAG
> B550 Tomahawk / in contrast MSI B550 MPG works fine).
> 
> When using standard USB wired keyboards via the BIOS emulation layer,
> GRUB experiences an extreme key bounce effect (every keypress is
> registered 5-20 times). If a navigation key (like Arrow Down) is held
> down, the entire system locks up instantly. The CPU core goes into a
> hard lockup/busy-loop (power draw increases by 30W, fans spin up).
> 
> I have tried forcing `GRUB_TERMINAL_INPUT="at_keyboard"`, but the issue
> persists. It seems the BIOS emulated keyboard driver fires interrupts at
> an unthrottled rate, and GRUB's real-mode/protected-mode input handler
> has no built-in software debouncing or polling-rate limitation to reject
> these rapid duplicate packets.
> 
> Would it be possible to implement a basic input dumper/debouncer or a
> slight delay loop inside the legacy keyboard polling routine to prevent
> such hardware interrupt storms from freezing the bootloader?
> 
> Best regards.
> 
> 
> 
> (Mail was generated by gemini due to my bad English.)
> 
> 
>