Dealing with a sensor which doesn't have valid reading until host is powered up

Alex Qiu xqiu at
Fri Aug 28 07:49:42 AEST 2020

Hi James,

After some debugging, I realized that the code I pointed out earlier wasn't
the root cause. Update is that, the HwmonTempSensor stops updating after
the hwmon driver returns EAGAIN as errno. I'll keep debugging...

- Alex Qiu

On Tue, Aug 25, 2020 at 5:49 PM Alex Qiu <xqiu at> wrote:

> Hi James and OpenBMC community,
> We have a sensor for HwmonTempSensor which doesn't have a valid reading
> until the host is fully booted. Before it's becoming alive and useful, it's
> getting disabled in code (
> because of errors thrown up by the hwmon driver. Ideally, the thermal
> control loop should kick the fan to fail safe mode until no more errors are
> observed.
> Any suggestions on how we should handle this kind of sensor properly?
> Thank you!
> - Alex Qiu
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