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From: Ed Tanous <edtanous@google.com>
Date: Mon, 15 Nov 2021 15:31:23 -0800
Message-ID: <CAH2-KxCzp3WvMB855WPYU8_2_9DQE5jGvzD+ugso6fKAP1R2kQ@mail.gmail.com>
Subject: Re: phosphor-pid-control: PWM not changing back from Manual to Auto
 mode
To: Charles Boyer <Charles.Boyer@fii-usa.com>
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On Mon, Nov 15, 2021 at 3:20 PM Charles Boyer <Charles.Boyer@fii-usa.com> w=
rote:
>
> Hello Josh and Ed,
>
> I used the OEM IPMI command to enter Manual mode of phosphor-pid-control,=
 and then I set the PWM value. After leaving Manual mode, I would expect sw=
ampd to bring the PWM back to the value from before entering Manual mode. H=
owever, the PWM remains the value I set in Manual mode. Although, when I in=
duced a temperature sensor to approach its setpoint, I observed the PWM to =
change.
>
> I believe the reason is because of https://github.com/openbmc/phosphor-pi=
d-control/blob/cca9c659889d149c06e95bab4b8808db4f1e3eab/dbus/dbuswrite.cpp#=
L69. My system uses DBus fan sensors, so the fan controller will call upon =
DbusWritePercent::write, which writes the calculated output value (ovalue) =
if it is different than the oldValue. When I enter Manual mode and set the =
PWM, the oldValue does not change; when I exit Manual mode, the ovalue and =
oldValue are the same as before Manual mode, so it skips the PWM write.
>
> How can the PWM "immediately" return to its original value from before Ma=
nual mode?

This is a known issue.  as the insecure validation feature was
defined, it required a full bmc reboot to reset all state at the end
of a validation/debug/tuning session.  This is one instance of many
where "best effort" clearly isn't good enough, although I'd be happy
to see patches to make the behavior better.

>
> Thanks,
> Charles
>