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

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Date:   Thu, 24 Dec 2020 16:00:49 +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()

24.12.2020 09:43, Viresh Kumar пишет:
> On 23-12-20, 23:37, Dmitry Osipenko wrote:
>> 23.12.2020 07:19, Viresh Kumar пишет:
>>> On 22-12-20, 22:15, Dmitry Osipenko wrote:
>>>> 22.12.2020 09:42, Viresh Kumar пишет:
>>>>> On 17-12-20, 21:06, Dmitry Osipenko wrote:
>>>>>> Add a ceil version of the dev_pm_opp_find_level(). It's handy to have if
>>>>>> levels don't start from 0 in OPP table and zero usually means a minimal
>>>>>> level.
>>>>>>
>>>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>>>
>>>>> Why doesn't the exact version work for you here ?
>>>>>
>>>>
>>>> The exact version won't find OPP for level=0 if levels don't start with
>>>> 0, where 0 means that minimal level is desired.
>>>
>>> Right, but why do you need to send 0 for your platform ?
>>>
>>
>> To put power domain into the lowest performance state when device is idling.
> 
> I see. So you really want to set it to the lowest state or just take the vote
> out ? Which may end up powering off the domain in the worst case ?
> 

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.