[PATCH v5] regulator: core: Resolve supply name earlier to prevent double-init

[Saravana Kannan]

On Fri, Feb 17, 2023 at 4:01 PM Christian Kohlschütter
<christian at kohlschutter.com> wrote:
>
> On 18. Feb 2023, at 00:46, Saravana Kannan <saravanak at google.com> wrote:
> >
> > On Fri, Feb 17, 2023 at 3:33 PM Christian Kohlschütter
> > <christian at kohlschutter.com> wrote:
> >>
> >> On 18. Feb 2023, at 00:22, Saravana Kannan <saravanak at google.com> wrote:
> >>>
> >>> On Thu, Aug 25, 2022 at 2:28 PM Christian Kohlschütter
> >>> <christian at kohlschutter.com> wrote:
> >>>>
> >>>> Previously, an unresolved regulator supply reference upon calling
> >>>> regulator_register on an always-on or boot-on regulator caused
> >>>> set_machine_constraints to be called twice.
> >>>>
> >>>> This in turn may initialize the regulator twice, leading to voltage
> >>>> glitches that are timing-dependent. A simple, unrelated configuration
> >>>> change may be enough to hide this problem, only to be surfaced by
> >>>> chance.
> >>>
> >>> In your case, can you elaborate which part of the constraints/init
> >>> twice caused the issue?
> >>>
> >>> I'm trying to simplify some of the supply resolving code and I'm
> >>> trying to not break your use case.
> >>>
> >>> -Saravana
> >>
> >> Here's a write-up of my use case, and how we got to the solution:
> >> https://kohlschuetter.github.io/blog/posts/2022/10/28/linux-nanopi-r4s/
> >
> > I did read the write up before I sent my request. I'm asking for
> > specifics on which functions in the set_machine_constraints() was
> > causing the issue. And it's also a bit unclear to me if the issue was
> > with having stuff called twice on the alway-on regulator or the
> > supply.
> >
> > -Saravana
>
> I'm afraid I cannot give a more detailed answer than what's in the write up and the previous discussion on this mailing list; I thought it's pretty detailed already.

Well, I do my best not to break your use case with whatever info you
are willing to provide. We'll figure it out one way or another I
suppose.

> However, it should be relatively straightforward to reproduce the issue.

If one has the hardware. Which I don't.

-Saravana