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Subject: Re: [PATCH v5] regulator: core: Resolve supply name earlier to
 prevent double-init
From:   =?utf-8?Q?Christian_Kohlsch=C3=BCtter?= 
        <christian@kohlschutter.com>
In-Reply-To: <CAGETcx_OKA+MkExc98337kZYKsoJtV0ZdfYJE7Tk00CFvCt2bA@mail.gmail.com>
Date:   Sat, 18 Feb 2023 01:01:30 +0100
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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References: <932DEB17-70FB-4416-80B3-C48A7C31848F@kohlschutter.com>
 <20220825212842.7176-1-christian@kohlschutter.com>
 <CAGETcx__Ez8i9O2O30-Q1R00xOqBjkKMCwt37_AGAQjNvZqpdg@mail.gmail.com>
 <B6E001E2-9BCD-420A-B0F6-1495DE46955E@kohlschutter.com>
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To:     Saravana Kannan <saravanak@google.com>
Precedence: bulk

On 18. Feb 2023, at 00:46, Saravana Kannan <saravanak@google.com> wrote:
>=20
> On Fri, Feb 17, 2023 at 3:33 PM Christian Kohlsch=C3=BCtter
> <christian@kohlschutter.com> wrote:
>>=20
>> On 18. Feb 2023, at 00:22, Saravana Kannan <saravanak@google.com> =
wrote:
>>>=20
>>> On Thu, Aug 25, 2022 at 2:28 PM Christian Kohlsch=C3=BCtter
>>> <christian@kohlschutter.com> wrote:
>>>>=20
>>>> 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.
>>>>=20
>>>> 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.
>>>=20
>>> In your case, can you elaborate which part of the constraints/init
>>> twice caused the issue?
>>>=20
>>> I'm trying to simplify some of the supply resolving code and I'm
>>> trying to not break your use case.
>>>=20
>>> -Saravana
>>=20
>> 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/
>=20
> 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.
>=20
> -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.