Re: [PATCH] comedi: comedi_test: avoid AI scan timing overflow

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

On Tue, Jun 09, 2026 at 12:14:04AM +0000, Samuel Moelius wrote:
> `waveform_ai_cmdtest()` tries to keep timer-driven analog-input scans
> representable by limiting `convert_arg` and by making `scan_begin_arg`
> at least `convert_arg * scan_end_arg`.

Please don't use markdown crud in changelog comments :(

> The conversion clamp tested `scan_begin_arg == TRIG_TIMER` instead of
> `scan_begin_src == TRIG_TIMER`, so normal timer scans skipped the clamp.
> The later product was computed in `unsigned int`, allowing a large
> conversion period to wrap and produce an accepted command whose true
> scan conversion time exceeds the scan period.

Is that a real problem as this is a test module?

> Require timer conversions to be at least one microsecond, apply the
> conversion limit when `scan_begin_src` is `TRIG_TIMER`, keep that limit
> on the same microsecond granularity as the rounded argument, and compute
> the scan-period floor in 64-bit before clamping it back to the ioctl
> argument range.
> 
> Assisted-by: Codex:gpt-5.5-cyber-preview
> Signed-off-by: Samuel Moelius <sam.moelius@trailofbits.com>

What commit id does this fix?  How was this tested?

thanks,

greg k-h