On Wed, May 27, 2026 at 11:18:52PM +0800, 占wei wrote:
> Thanks for the detailed explanation -- that make sense
>
> I can think of two paths forward:
>
> 1) Have fan_input_read() return -ENODATA if one channel has started
> reporting pulses but another remains silent for, say, 30 seconds.
> This way the phantom entry still appears in sysfs but userspace
> tools like `sensors` can handle the "no data" case gracefully
> instead of showing a misleading 0 RPM.
Sounds a bit over engineered solution with its own caveats because
a) We assume that both channels are monitored simultaneously and first
channel actually reports non-zero value for 30 seconds (or whatever
trivial value we device) continuously, which is not guaranteed.
b) This means the output of one channel depends on another and I'm
doubtful if maintainers would be okay with such hacks.
> 2) Drop the code change entirely and instead add a short note in
> Documentation/gpu/xe/xe_hwmon.rst explaining that on DG2 boards
> where the OEM routes multiple physical fans through a shared tach
> line, fan{2,3}_input may read 0, so future contributors don't end
> up re-attempting the same v1 patch I just sent.
This one makes more sense to me though.
Raag
