[pmbusplus] userspace i2c, pmbus interactions

Patrick Williams patrick at stwcx.xyz
Sat May 1 06:47:25 AEST 2021

On Fri, Apr 30, 2021 at 08:53:27AM -0700, Jason Ling wrote:
> Yup, this definitely isn't pleasant but it's doable. Have you had
> experiences where unbinding/binding caused lots of pain? The only pain that
> I've seen is that telemetry daemons generally don't take well to having
> hwmon sysfs attributes yanked from underneath them.

Yes, our current hwmon daemons don't take kindly to the device being
pulled out from underneath them.  That's the big concern.

On top of that, other daemons that consume those sensor readings don't
really like the sensor going away either.

> Just spitballing.. but for devices that need to be upgradeable *and* need
> to report telemetry, that such things should be done in a single service
> and perhaps it makes the most sense to do it all in userspace (to avoid
> ugly unbinding/binding).

This is not ideal to me, if I'm understanding what you wrote correctly.
It means that any PMBus device for which we want to do upgrade we won't
be using the pmbus+hwmon subsystem but instead have to rewrite it all
ourselves in userspace.

My top preference would be to work with upstream about supporting field
upgrade on devices.  Second would be to figure out how to safely
bind/unbind.  Reimplenting what the kernel already has and we already
leverage should be way down our preference list.

Patrick Williams
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