linux-kernel - Re: [PATCH v2 11/48] opp: Add dev_pm_opp_find_level

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Date:   Wed, 30 Dec 2020 17:02:11 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Peter Geis <pgwipeout@...il.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-media@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v2 11/48] opp: Add dev_pm_opp_find_level_ceil()

30.12.2020 07:46, Viresh Kumar пишет:
> On 28-12-20, 17:03, Dmitry Osipenko wrote:
>> 28.12.2020 09:22, Viresh Kumar пишет:
>>> On 24-12-20, 16:00, Dmitry Osipenko wrote:
>>>> In a device driver I want to set PD to the lowest performance state by
>>>> removing the performance vote when dev_pm_opp_set_rate(dev, 0) is
>>>> invoked by the driver.
>>>>
>>>> The OPP core already does this, but if OPP levels don't start from 0 in
>>>> a device-tree for PD, then it currently doesn't work since there is a
>>>> need to get a rounded-up performance state because
>>>> dev_pm_opp_set_voltage() takes OPP entry for the argument (patches 9 and
>>>> 28).
>>>>
>>>> The PD powering off and performance-changes are separate from each other
>>>> in the GENPD core. The GENPD core automatically turns off domain when
>>>> all devices within the domain are suspended by system-suspend or RPM.
>>>>
>>>> The performance state of a power domain is controlled solely by a device
>>>> driver. GENPD core only aggregates the performance requests, it doesn't
>>>> change the performance state of a domain by itself when device is
>>>> suspended or resumed, IIUC this is intentional. And I want to put domain
>>>> into lowest performance state when device is suspended.
>>>
>>> Right, so if you really want to just drop the performance vote, then with a
>>> value of 0 for the performance state the call will reach to your genpd's
>>> callback ->set_performance_state(). Just as dev_pm_opp_set_rate() accepts the
>>> frequency to be 0, I would expect dev_pm_opp_set_rate() to accept opp argument
>>> as NULL and in that case set voltage to 0 and do regulator_disable() as well.
>>> Won't that work better than going for the lowest voltage ?
>>>
>>
>> We can make dev_pm_opp_set_voltage() to accept OPP=NULL in order to
>> disable the regulator, like it's done for dev_pm_opp_set_rate(dev, 0).
>> Although, I don't need this kind of behaviour for the Tegra PD driver,
>> and thus, would prefer to leave this for somebody else to implement in
>> the future, once it will be really needed.
>>
>> Still we need the dev_pm_opp_find_level_ceil() because level=0 means
>> that we want to set PD to the lowest (minimal) performance state, i.e.
>> it doesn't necessarily mean that we want to set the voltage to 0 and
>> disable the PD entirely. GENPD has a separate controls for on/off.
> 
> Ok.
> 

I'll separate the OPP patches from this series and will prepare v3,
thank you for the review!