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From:   Saravana Kannan <saravanak@google.com>
Date:   Fri, 17 Feb 2023 15:46:17 -0800
Message-ID: <CAGETcx_OKA+MkExc98337kZYKsoJtV0ZdfYJE7Tk00CFvCt2bA@mail.gmail.com>
Subject: Re: [PATCH v5] regulator: core: Resolve supply name earlier to
 prevent double-init
To:     =?UTF-8?Q?Christian_Kohlsch=C3=BCtter?= 
        <christian@kohlschutter.com>
Cc:     Mark Brown <broonie@kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        =?UTF-8?Q?Heiko_St=C3=BCbner?= <heiko@sntech.de>,
        lgirdwood@gmail.com, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-mmc@vger.kernel.org,
        linux-rockchip@lists.infradead.org, m.reichl@fivetechno.de,
        robin.murphy@arm.com, vincent.legoll@gmail.com, wens@kernel.org
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On Fri, Feb 17, 2023 at 3:33 PM Christian Kohlsch=C3=BCtter
<christian@kohlschutter.com> wrote:
>
> On 18. Feb 2023, at 00:22, Saravana Kannan <saravanak@google.com> wrote:
> >
> > On Thu, Aug 25, 2022 at 2:28 PM Christian Kohlsch=C3=BCtter
> > <christian@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