linux-kernel - Re: [PATCH] regulator: qcom-rpmh: Revert "regulator: qcom-rpmh: Use PROBE_FORCE

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Date:   Thu, 15 Jun 2023 00:32:45 +0530
From:   Amit Pundir <amit.pundir@...aro.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Mark Brown <broonie@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Caleb Connolly <caleb.connolly@...aro.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regulator: qcom-rpmh: Revert "regulator: qcom-rpmh: Use PROBE_FORCE_SYNCHRONOUS"

On Wed, 7 Jun 2023 at 04:59, Doug Anderson <dianders@...omium.org> wrote:
>
> From a black box perspective, I guess the things I could think of
> would be to keep poking around with things that you control. Best
> ideas I have:
>
> 1. Use "bisect" style techniques to figure out how much you really
> need to move the "lvs" regulators. Try moving it halfway up the list.
> If that works, move it closer to the bottom. If that doesn't work,
> move it closer to the top. Eventually you'd find out which regulator
> it's important to be before.

Hi, I tried this bisect style technique to move lvs regulators up in
the list gradually and I found that they need to be enabled atleast
before ldo12 and the ldo regulators which follow the ldo12 in the
list.

>
> 2. Try adding some delays to some of the regulators with
> "regulator-enable-ramp-delay" and/or "regulator-settling-time-us".
> Without a scope, it'll be tricky to figure out exactly which
> regulators might need delays, but you could at least confirm if the
> "overkill" approach of having all the regulators have some delay
> helps... I guess you could also try putting a big delay for "ldo26".
> If that works, you could try moving it up (again using a bisect style
> approach) to see where the delay matters?

I tried this approach as well earlier today but I don't know how big
"the big" delay can be. The device fails to boot if I add a settling
time of as much as 2sec per each ldo and lvs regulator too. I didn't
try increasing the delay further.

Regards,
Amit Pundir