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

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Date:   Wed, 18 Aug 2021 11:30:34 +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>,
        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

On 18-08-21, 11:28, Viresh Kumar wrote:
> On 18-08-21, 08:21, Dmitry Osipenko wrote:
> > Yes, GENPD will cache the perf state across suspend/resume and initially
> > cached value is out of sync with h/w.
> > 
> > Nothing else. But let me clarify it all again.
> 
> Thanks for your explanation.
> 
> > Initially the performance state of all GENPDs is 0 for all devices.
> > 
> > The clock rate is preinitialized for all devices to a some default rate
> > by clk driver, or by bootloader or by assigned-clocks in DT.
> > 
> > When device is rpm-resumed, the resume callback of a device driver
> > enables the clock.
> > 
> > Before clock is enabled, the voltage needs to be configured in
> > accordance to the clk rate.
> > 
> > So now we have a GENPD with pstate=0 on a first rpm-resume, which
> > doesn't match the h/w configuration. Calling dev_pm_opp_sync() sets the
> > pstate in accordance to the h/w config.
> 
> What about calling dev_pm_opp_set_rate(dev, clk_get_rate(dev)) here
> instead ? That will work, right ? The advantage is it works without
> any special routine to do so.
> 
> I also wonder looking at your gr3d.c changes, you set a set-opp
> helper, but the driver doesn't call set_opp_rate at all. Who calls it
> ?
> 
> And if it is all about just syncing the genpd core, then can the genpd
> core do something like what clk framework does? i.e. allow a new
> optional genpd callback, get_performance_state() (just like
> set_performance_state()), which can be called initially by the core to
> get the performance to something other than zero. opp-set-rate is
> there to set the performance state and enable the stuff as well.
> That's why it looks incorrect in your case, where the function was
> only required to be called once, and you are ending up calling it on
> each resume. Limiting that with another local variable is bad as well.

Ulf, this last part is for you :)

-- 
viresh