linux-kernel - Re: [PATCH v8 01/34] opp: Add dev_pm_opp

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Message-ID: <6df0ed60-e497-0af2-09b6-a9d82f502f17@gmail.com>
Date:   Wed, 18 Aug 2021 07:29:38 +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>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Peter Chen <peter.chen@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-spi@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-mmc@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v8 01/34] opp: Add dev_pm_opp_sync() helper

18.08.2021 07:12, Dmitry Osipenko пишет:
> 18.08.2021 06:55, Viresh Kumar пишет:
>> On 17-08-21, 18:49, Dmitry Osipenko wrote:
>>> 17.08.2021 10:55, Viresh Kumar пишет:
>>> ...
>>>>> +int dev_pm_opp_sync(struct device *dev)
>>>>> +{
>>>>> +	struct opp_table *opp_table;
>>>>> +	struct dev_pm_opp *opp;
>>>>> +	int ret = 0;
>>>>> +
>>>>> +	/* Device may not have OPP table */
>>>>> +	opp_table = _find_opp_table(dev);
>>>>> +	if (IS_ERR(opp_table))
>>>>> +		return 0;
>>>>> +
>>>>> +	if (!_get_opp_count(opp_table))
>>>>> +		goto put_table;
>>>>> +
>>>>> +	opp = _find_current_opp(dev, opp_table);
>>>>> +	ret = _set_opp(dev, opp_table, opp, opp->rate);
>>>>
>>>> And I am not sure how this will end up working, since new OPP will be
>>>> equal to old one. Since I see you call this from resume() at many
>>>> places.
>>>
>>> Initially OPP table is "uninitialized" and opp_table->enabled=false,
>>> hence the first sync always works even if OPP is equal to old one. Once
>>> OPP has been synced, all further syncs are NO-OPs, hence it doesn't
>>> matter how many times syncing is called.
>>>
>>> https://elixir.bootlin.com/linux/v5.14-rc6/source/drivers/opp/core.c#L1012
>>
>> Right, but how will this work from Resume ? Won't that be a no-op ?
> 
> The first resume initializes the OPP state on sync, all further syncs on
> resume are no-ops.
> 

Notice that we use GENPD here. GENPD core takes care of storing PD's
performance state (voltage in case of Tegra) and dropping it to 0 after
rpm-suspend, GENPD core also restores the state before rpm-resume.