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

[Saravana Kannan]

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