linux-kernel - Re: [PATCH] regulator: core: Skip balancing of the enabled regulators in regulator

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 8 Oct 2019 18:02:36 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     linux-kernel@...r.kernel.org, Liam Girdwood <lgirdwood@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-samsung-soc@...r.kernel.org,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Kamil Konieczny <k.konieczny@...sung.com>
Subject: Re: [PATCH] regulator: core: Skip balancing of the enabled regulators
 in regulator_enable()

08.10.2019 16:24, Bartlomiej Zolnierkiewicz пишет:
> 
> On 10/8/19 2:47 PM, Mark Brown wrote:
>> On Tue, Oct 08, 2019 at 02:38:55PM +0200, Marek Szyprowski wrote:
>>
>>> Then if I get it right, the issue is caused by the commit 7f93ff73f7c8 
>>> ("opp: core: add regulators enable and disable"). I've checked and 
>>> indeed reverting it fixes Peach Pi to boot properly.

Yes, please note that the "ww_mutex" patch didn't change the original logic and only
rearranged the code a tad.

 The question is if
>>> this is desired behavior or not?
>>
>> That doesn't seem ideal - either it's redundant for regulators that need
>> to be marked as always-on anyway or it's going to force the regulators
>> on when a device could do runtime PM (eg, if the same code can run on
>> something like a GPU which can be turned off while the screen is off or
>> is displaying a static image).
> 
> Commit 7f93ff73f7c8 ("opp: core: add regulators enable and disable")
> currently can be safely reverted as all affected users use always-on
> regulators. However IMHO it should be possible to enable always-on
> regulator without side-effects.
> 
> When it comes to setting regulator constraints before doing enable
> operation, it also seems to be possible solution but would require
> splitting regulator_set_voltage() operation on two functions:
> 
> - one for setting constraints (before regulator_enable() operation)
> 
> - the other one actually setting voltage (after enable operation)
> 
> Unfortunately this is much bigger task and doesn't seem to be -rc
> time material so I'm in favor of just applying Marek's fix as it is
> for now.

That OPP patch caused the same problem for the NVIDIA Tegra20 CPUFreq driver (in-progress)
and I resolved it in the coupler's code [0]. Perhaps the generic coupler could do the same
thing by assuming that min_uV=current_uV until any consumer sets the voltage, i.e. if
regulator_check_consumers(min_uV=0) returns min_uV=0.

[0] https://lkml.org/lkml/2019/7/25/892