[PATCH v5 03/16] power: sequencing: Add pwrseq_power_is_on()

[Chen-Yu Tsai]

On Wed, Jul 15, 2026 at 8:10 PM Bartosz Golaszewski <brgl at kernel.org> wrote:
>
> On Wed, 15 Jul 2026 11:29:02 +0200, Andy Shevchenko
> <andriy.shevchenko at linux.intel.com> said:
> > On Wed, Jul 15, 2026 at 04:53:33PM +0800, Chen-Yu Tsai wrote:
> >> The power sequencing consumer API already does power on state tracking
> >> internally. Expose the state to consumers through pwrseq_power_is_on()
> >> so that they don't have to reimplement it locally.
> >
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
> >
> > ...
> >
> >> +/**
> >> + * pwrseq_power_is_on() - Queries the last requested state of the power sequencer.
> >> + * @desc: Descriptor referencing the power sequencer.
> >> + *
> >> + * This returns the last requested state of the power sequencer.
> >> + *
> >> + * Returns:
> >> + * On success, 1 for on or desc is NULL (optional) and 0 for off;
> >> + * negative error number on failure.
> >
> > I would rephrase it a bit.
> >
> >  * On success, 1 for on and 0 for off; negative error number on failure.
> >  * If desc is NULL (means optional) return 1.
> >
> > And this rises a question: why 1? Shouldn't it be some "unknown" state?
> > (But since Bart Acked this, this doesn't prevent the patch to go, you
> >  got my tag above.)
> >
>
> No, this is good feedback. Maybe we should prefer an enum like so:
>
> enum pwrseq_state {
>         PWRSEQ_POWER_UNKNOWN,
>         PWRSEQ_POWER_ON,
>         PWRSEQ_POWER_OFF
> };

Well I think the crux of it is whether the API considers the descriptor
optional. The power on/off functions suggest that is the case.

I modeled this on reset_control_status(). I believe the rationale is that
if the reset control or pwrseq is optional, then either there is some
other mechanism to deal with the reset (GPIO) or pwrseq (GPIO + regulator),
or it's always on and operational.

In such cases and the rare case where one has to query the state, the
queries are possibly chained together and I think it makes sense to
assume the "operational" state as the fallback.

If this returns an enum, then I think the previous approach of returning
an error value for an invalid descriptor is better. One doesn't need to
learn a new set of return values.

I'm fine either way. I would just move the checks over to the consumer
side. But I think the principles guiding the overall API design is
something you need to provide:

  - Is the descriptor optional? What should the action functions
    (power on / off , or query status) return when NULL is given?
  - Is the subsystem optional? Should the stub functions besides
    pwrseq_get() return 0 instead of -ENOSYS?

Right now the API feels like the descriptor is optional but the
subsystem is not. One has to add IS_ENABLED(CONFIG_POWER_SEQUENCING)
around the consumer API to make it an optional feature.


Thanks
ChenYu