linux-kernel - Re: [PATCH v8 07/34] clk: tegra: Support runtime PM and power domain

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Date:   Fri, 20 Aug 2021 15:08:10 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Dmitry Osipenko <digetx@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        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 Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux USB List <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 <linux-mmc@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v8 07/34] clk: tegra: Support runtime PM and power domain

[...]

> >
> > I'm creating platform device for the clocks that require DVFS. These
> > clocks don't use regulator, they are attached to the CORE domain.
> > GENPD framework manages the performance state, aggregating perf votes
> > from each device, i.e. from each clock individually.
> >
> > You want to reinvent another layer of aggregation on top of GENPD.
> > This doesn't worth the effort, we won't get anything from it, it
> > should be a lot of extra complexity for nothing. We will also lose
> > from it because pm_genpd_summary won't show you a per-device info.
> >
> > domain                          status          children                           performance
> >     /device                                             runtime status
> > ----------------------------------------------------------------------------------------------
> > heg                             on                                                 1000000
> >     /devices/soc0/50000000.host1x                       active                     1000000
> >     /devices/soc0/50000000.host1x/54140000.gr2d         suspended                  0
> > mpe                             off-0                                              0
> > vdec                            off-0                                              0
> >     /devices/soc0/6001a000.vde                          suspended                  0
> > venc                            off-0                                              0
> > 3d1                             off-0                                              0
> >     /devices/genpd:1:54180000.gr3d                      suspended                  0
> > 3d0                             off-0                                              0
> >     /devices/genpd:0:54180000.gr3d                      suspended                  0
> > core-domain                     on                                                 1000000
> >                                                 3d0, 3d1, venc, vdec, mpe, heg
> >     /devices/soc0/7d000000.usb                          active                     1000000
> >     /devices/soc0/78000400.mmc                          active                     950000
> >     /devices/soc0/7000f400.memory-controller            unsupported                1000000
> >     /devices/soc0/7000a000.pwm                          active                     1000000
> >     /devices/soc0/60006000.clock/tegra_clk_pll_c        active                     1000000
> >     /devices/soc0/60006000.clock/tegra_clk_pll_e        suspended                  0
> >     /devices/soc0/60006000.clock/tegra_clk_pll_m        active                     1000000
> >     /devices/soc0/60006000.clock/tegra_clk_sclk         active                     1000000
> >
>
> I suppose if there's really no good way of doing this other than
> providing a struct device, then so be it. I think the cleaned up sysfs
> shown in the summary above looks much better than what the original
> would've looked like.
>
> Perhaps an additional tweak to that would be to not create platform
> devices. Instead, just create struct device. Those really have
> everything you need (.of_node, and can be used with RPM and GENPD). As I
> mentioned earlier, platform device implies a CPU-memory-mapped bus,
> which this clearly isn't. It's kind of a separate "bus" if you want, so
> just using struct device directly seems more appropriate.

Just a heads up. If you don't use a platform device or have a driver
associated with it for probing, you need to manage the attachment to
genpd yourself. That means calling one of the dev_pm_domain_attach*()
APIs, but that's perfectly fine, ofcourse.

>
> We did something similar for XUSB pads, see drivers/phy/tegra/xusb.[ch]
> for an example of how that was done. I think you can do something
> similar here.
>
> Thierry

Kind regards
Uffe