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

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Message-ID: <710261d9-7ae3-5155-c0a2-f8aed2408d0b@gmail.com>
Date:   Tue, 17 Aug 2021 18:49:03 +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

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

> what exactly are you trying to do here ? Those details would be good
> to have in commit log as well, I haven't really followed V7 of your
> series.

I'm initializing voltage/power state of OPP table in accordance to the
clock rate, bumping voltage before clock is enabled by device driver.
I'll improve the commit message.

An alternative to the explicit syncing could be something like a new
dev_pm_opp_resume/suspend helpers that will take care of
enabling/disabling the OPP table clock/etc and syncing the OPP state
with h/w.