On Thu, Oct 27, 2022 at 09:12:22PM -0700, Zev Weiss wrote: > I can see why it might look that way, but I'd argue it's actually not. The > systems this is intended to support provide power to entirely separate > external devices -- think of a power distribution unit that might have > arbitrary things plugged into it. It seems to me like a property of the > hardware that those things shouldn't have their power supply turned off (or > on) just because a controller in the PDU rebooted. We don't turn things off on reboot? We don't do anything in particular on reboot... > > I guess it easy > > to understand in case of Linux which disables unclaimed regulators > > during. But what if other system/firmware does not behave like that? > In this case, then no change would be needed -- a system that (unlike Linux) > doesn't twiddle regulator state on its own would just continue to not do > that. We don't turn unclaimed regulators off until userspace has had a chance to start, if there's some problem with system integrators arranging to do this we can look into how that works, for example making the delay tunable. I don't think this is really meaningfully different from a driver deciding to turn things off from a binding point of view. > > And what is the "external actor"? OS is not an external actor? > It's admittedly a bit vague, but I couldn't think of a clearer way to > express what is a sort of nebulous concept -- essentially, some entity > outside the "driver" (or analogous software component) using the information > in the device-tree. In many common cases this would essentially mean "a > human user", since in the PDU-like systems I'm targeting here the only thing > that should ever be deciding to turn the regulator on or off is an operator > logged in to the system to manually enable or disable an outlet. I was > aiming to leave the wording a bit more general though, since in some other > context I could imagine some other piece of software toggling things > automatedly (e.g. lights getting turned on and off on a schedule or > something, if that's what happens to be plugged in). This is policy stuff, it doesn't translate into DTs at all. > > I could not get the problem you want to solve with this property - I > > looked at cover letter and at commit msg. > The problem is that a driver deciding on its own to enable or disable the > regulator (e.g. during boot or shutdown) would be a critical failure for the > kind of systems I'm aiming to support. If the driver is doing something like this it should be addressed in the driver. > > I can only imagine that you want to keep regulator on, after last its > > user disappears... but for what purpose? Do you expect that after system > > shutdown the pin will stay high so regulator will be also on? If so, you > > need hardware design, e.g. with some pull up (if control is over GPIO). > As described above, the regulators involved here (in these sorts of PDU-like > systems) provide power for external systems and devices. It is critical > that the controller's boot and shutdown sequences not alter the state of the > regulator. This really sounds like a full stack system integration problem, not something that can be resolved with one software component.
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