linux-kernel - Re: [PATCH 1/4] PM / EM: and devices to Energy Model

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Message-ID: <20200120150918.GA164543@google.com>
Date:   Mon, 20 Jan 2020 15:09:18 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-omap@...r.kernel.org,
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        linux-imx@....com, Morten.Rasmussen@....com,
        Dietmar.Eggemann@....com, Chris.Redpath@....com,
        ionela.voinescu@....com, javi.merino@....com,
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Subject: Re: [PATCH 1/4] PM / EM: and devices to Energy Model

Hey Lukasz,

On Monday 20 Jan 2020 at 14:52:07 (+0000), Lukasz Luba wrote:
> On 1/17/20 10:54 AM, Quentin Perret wrote:
> > Suggested alternative: have two registration functions like so:
> > 
> > 	int em_register_dev_pd(struct device *dev, unsigned int nr_states,
> > 			       struct em_data_callback *cb);
> > 	int em_register_cpu_pd(cpumask_t *span, unsigned int nr_states,
> > 			       struct em_data_callback *cb);
> 
> Interesting, in the internal review Dietmar asked me to remove these two
> functions. I had the same idea, which would simplify a bit the
> registration and it does not need to check the dev->bus if it is CPU.
> 
> Unfortunately, we would need also two function in drivers/opp/of.c:
> dev_pm_opp_of_register_cpu_em(policy->cpus);
> and
> dev_pm_opp_of_register_dev_em(dev);
> 
> Thus, I have created only one registration function, which you can see
> in this patch set.

Right, I can see how having a unified API would be appealing, but the
OPP dependency is a nono, so we'll need to work around one way or
another.

FWIW, I don't think having separate APIs for CPUs and other devices is
that bad given that we already have entirely different frameworks to
drive their respective frequencies. And the _cpu variants are basically
just wrappers around the _dev ones, so not too bad either IMO :).

Thanks,
Quentin