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

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Message-Id: <F6AC6A52-49BA-4F80-91A8-271E11CD17E4@kohlschutter.com>
Date:   Sat, 18 Feb 2023 01:01:30 +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 00:46, Saravana Kannan <saravanak@...gle.com> wrote:
> 
> 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

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.

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