linux-kernel - Re: [PATCH] regulator: do not balance regulators without constraints

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Message-ID: <56e496bc-172f-d62f-5376-c8d734af6a51@samsung.com>
Date:   Fri, 29 May 2020 07:45:06 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>, peron.clem@...il.com,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        linux-samsung-soc@...r.kernel.org,
        Chanwoo Choi <cw00.choi@...sung.com>
Subject: Re: [PATCH] regulator: do not balance regulators without
 constraints

Hi Mark,

On 28.05.2020 15:43, Mark Brown wrote:
> On Thu, May 28, 2020 at 03:11:30PM +0200, Marek Szyprowski wrote:
>> Balancing coupled regulators must wait until the clients for all of the
>> coupled regualtors set their constraints, otherwise the balancing code
>> might change the voltage of the not-yet-constrained regulator to the
>> value below the bootloader-configured operation point, what might cause a
>> system crash.
> This forces every supply to have something which explicitly manages
> voltages which means that if one of the coupled supplies doesn't really
> care about the voltage (perhaps doesn't even have any explicit
> consumers) and just needs to be within a certain range of another supply
> then it'll end up restricting things needlessly.
Frankly, that's exactly what we need for Exynos5422 case. If devfreq 
driver is not enabled/compiled, we want to keep the "vdd_int" volatage 
unchanged. This confirms me that we really need to have a custom coupler 
for Exynos5422 case. It will solve such issues without adding hacks to 
regulator core.
> Saravana was trying to do some stuff with sync_state() which might be
> interesting here although I have concerns with that approach too:
>
>     https://lore.kernel.org/lkml/20200527074057.246606-1-saravanak@google.com/

This still doesn't solve the above mentioned case.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland