MIME-Version: 1.0
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> <CAGETcx_OKA+MkExc98337kZYKsoJtV0ZdfYJE7Tk00CFvCt2bA@mail.gmail.com>
 <F6AC6A52-49BA-4F80-91A8-271E11CD17E4@kohlschutter.com>
In-Reply-To: <F6AC6A52-49BA-4F80-91A8-271E11CD17E4@kohlschutter.com>
From:   Saravana Kannan <saravanak@google.com>
Date:   Fri, 17 Feb 2023 16:05:52 -0800
Message-ID: <CAGETcx839=FSj-njD03bqaEFKPfhEY7DXnjQ5V1+s0G2vn86Eg@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
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Feb 17, 2023 at 4:01 PM Christian Kohlsch=C3=BCtter
<christian@kohlschutter.com> wrote:
>
> On 18. Feb 2023, at 00:46, Saravana Kannan <saravanak@google.com> wrote:
> >
> > 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> wrot=
e:
> >>>
> >>> 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 configuratio=
n
> >>>> 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.

Well, I do my best not to break your use case with whatever info you
are willing to provide. We'll figure it out one way or another I
suppose.

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

If one has the hardware. Which I don't.

-Saravana