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

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Message-ID: <20210818055849.ybfajzu75ecpdrbn@vireshk-i7>
Date:   Wed, 18 Aug 2021 11:28:49 +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, 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.

> In a previous v7 I proposed to preset the rpm_pstate of GENPD (perf
> level that is restored before device is rpm-resumed) from PD's
> attach_dev callback, but Ulf didn't like that because it requires to use
> and modify GENPD 'private' variables from a PD driver. We decided that
> will be better to make device drivers to explicitly sync the perf state,
> which I implemented in this v8.

-- 
viresh