linux-kernel - Re: [PATCH 0/8] cpufreq: Auto-register with energy model

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Message-ID: <20210811091321.xtb776q4t6cwyanx@vireshk-i7>
Date:   Wed, 11 Aug 2021 14:43:21 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Vincent Donnefort <vincent.donnefort@....com>,
        lukasz.luba@....com, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Cristian Marussi <cristian.marussi@....com>,
        Fabio Estevam <festevam@...il.com>,
        Kevin Hilman <khilman@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-omap@...r.kernel.org
Subject: Re: [PATCH 0/8] cpufreq: Auto-register with energy model

On 11-08-21, 09:37, Quentin Perret wrote:
> On Wednesday 11 Aug 2021 at 10:48:59 (+0530), Viresh Kumar wrote:
> > I had to use the pm-opp version, since almost everyone was using that.
> > 
> > On the other hand, there isn't a lot of OPP specific stuff in
> > dev_pm_opp_of_register_em(). It just uses dev_pm_opp_get_opp_count(),
> > that's all. This ended up in the OPP core, nothing else. Maybe we can
> > now move it back to the EM core and name it differently ?
> 
> Well it also uses dev_pm_opp_find_freq_ceil() and
> dev_pm_opp_get_voltage(), so not sure how easy it will be to move, but
> if it is possible no objection from me.

What uses these routines ? dev_pm_opp_of_register_em() ? I am not able
to see that at least :(

> Right but the EM is a description of the hardware, so it seemed fair
> to assume this wouldn't change across the lifetime of the OS, similar
> to the DT which we can't reload at run-time. Yes it can be a little odd
> if you load/unload your driver module, but note that you generally can't
> load two completely different drivers on a single system. You'll just
> load the same one again and the hardware hasn't changed in the meantime,
> so the previously loaded EM will still be correct.

Yeah, it will be the same driver but a different version of it, which
may have updated the freq table. For me the EM is attached to the
freq-table, and the freq-table is not available anymore after the
driver is gone.

Anyway, I will leave that for you guys to decide :)

> I hear your argument
> about cpufreq driver development, but the locking involved to allow
> 'just' that is pretty involved, and nobody has complained about this
> specific issue so far, so that didn't seem worth it. If we do have good
> reasons to change the EM at runtime, then yes I think we should do it,
> it just didn't seem like that was the case until now.

-- 
viresh