linux-kernel - Re: [PATCH v2 28/48] soc/tegra: Introduce core power domain driver

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Date:   Wed, 23 Dec 2020 11:27:15 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
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 28/48] soc/tegra: Introduce core power domain driver

On 22-12-20, 22:39, Dmitry Osipenko wrote:
> 22.12.2020 22:21, Dmitry Osipenko пишет:
> >>> +	if (IS_ERR(opp)) {
> >>> +		dev_err(&genpd->dev, "failed to find OPP for level %u: %pe\n",
> >>> +			level, opp);
> >>> +		return PTR_ERR(opp);
> >>> +	}
> >>> +
> >>> +	err = dev_pm_opp_set_voltage(&genpd->dev, opp);
> >> IIUC, you implemented this callback because you want to use the voltage triplet
> >> present in the OPP table ?
> >>
> >> And so you are setting the regulator ("power") later in this patch ?
> > yes
> > 
> >> I am not in favor of implementing this routine, as it just adds a wrapper above
> >> the regulator API. What you should be doing rather is get the regulator by
> >> yourself here (instead of depending on the OPP core). And then you can do
> >> dev_pm_opp_get_voltage() here and set the voltage yourself. You may want to
> >> implement a version supporting triplet here though for the same.
> >>
> >> And you won't require the sync version of the API as well then.
> >>
> > That's what I initially did for this driver. I don't mind to revert back
> > to the initial variant in v3, it appeared to me that it will be nicer
> > and cleaner to have OPP API managing everything here.
> 
> I forgot one important detail (why the initial variant wasn't good)..
> OPP entries that have unsupportable voltages should be filtered out and
> OPP core performs the filtering only if regulator is assigned to the OPP
> table.
> 
> If regulator is assigned to the OPP table, then we need to use OPP API
> for driving the regulator, hence that's why I added
> dev_pm_opp_sync_regulators() and dev_pm_opp_set_voltage().
> 
> Perhaps it should be possible to add dev_pm_opp_get_regulator() that

What's wrong with getting the regulator in the driver as well ? Apart from the
OPP core ?

> will return the OPP table regulator in order to allow driver to use the
> regulator directly. But I'm not sure whether this is a much better
> option than the opp_sync_regulators() and opp_set_voltage() APIs.

set_voltage() is still fine as there is some data that the OPP core has, but
sync_regulator() has nothing to do with OPP core.

And this may lead to more wrapper helpers in the OPP core, which I am afraid of.
And so even if it is not the best, I would like the OPP core to provide the data
and not get into this. Ofcourse there is an exception to this, opp_set_rate.

-- 
viresh