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

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Message-Id: <B6E001E2-9BCD-420A-B0F6-1495DE46955E@kohlschutter.com>
Date:   Sat, 18 Feb 2023 00:33:20 +0100
From:   Christian Kohlschütter 
        <christian@...lschutter.com>
To:     Saravana Kannan <saravanak@...gle.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 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/