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

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Message-ID: <a2a3c41f-c5e4-ee7e-7d48-03af8bac8863@gmail.com>
Date:   Wed, 18 Aug 2021 07:37:46 +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 07:31, Viresh Kumar пишет:
> On 18-08-21, 07:12, Dmitry Osipenko wrote:
>> 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.
> 
> But the OPPs should already be initialized as someone must have called
> opp-set-rate earlier ? Why do this from resume and not probe ?

This will set voltage level without having an actively used hardware.
Take a 3d driver for example, if you set the rate on probe and
rpm-resume will never be called, then the voltage will be set high,
while hardware is kept suspended if userspace will never wake it up by
executing a 3d job.