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

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Date:   Fri, 17 Feb 2023 15:46:17 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Christian Kohlschütter 
        <christian@...lschutter.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Heiko Stübner <heiko@...ech.de>,
        lgirdwood@...il.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, m.reichl@...etechno.de,
        robin.murphy@....com, vincent.legoll@...il.com, wens@...nel.org
Subject: Re: [PATCH v5] regulator: core: Resolve supply name earlier to
 prevent double-init

On Fri, Feb 17, 2023 at 3:33 PM Christian Kohlschütter
<christian@...lschutter.com> wrote:
>
> On 18. Feb 2023, at 00:22, Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > On Thu, Aug 25, 2022 at 2:28 PM Christian Kohlschütter
> > <christian@...lschutter.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