linux-kernel - Re: [PATCH 09/12] devfreq: add mediatek cci devfreq

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Message-ID: <1590051155.14062.3.camel@mtksdaap41>
Date:   Thu, 21 May 2020 16:52:35 +0800
From:   <andrew-sh.cheng@...iatek.com>
To:     unlisted-recipients:; (no To-header on input)
CC:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        "Rob Herring" <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Nishanth Menon <nm@...com>, "Stephen Boyd" <sboyd@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        <linux-pm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <srv_heupstream@...iatek.com>
Subject: Re: [PATCH 09/12] devfreq: add mediatek cci devfreq


On Wed, 2020-05-20 at 13:31 +0100, Mark Brown wrote:
> On Wed, May 20, 2020 at 11:43:04AM +0800, Andrew-sh.Cheng wrote:
> 
> > +	cci_df->proc_reg = devm_regulator_get_optional(cci_dev, "proc");
> > +	ret = PTR_ERR_OR_ZERO(cci_df->proc_reg);
> > +	if (ret) {
> > +		if (ret != -EPROBE_DEFER)
> > +			dev_err(cci_dev, "failed to get regulator for CCI: %d\n",
> > +				ret);
> > +		return ret;
> > +	}
> > +	ret = regulator_enable(cci_df->proc_reg);
> 
> The code appears to require a regulator (and I'm guessing the device
> needs power) so why is this using regulator_get_optional()?

Hi Mark,

Do you mean, why not use regulator_get_exclusive() or regulator_get()?
Because cci and cpu litter core shared buck, it cannot use
regulator_get_exclusive().
Because both cci and cpu want to tune voltage, it cannot use
regulator_get(), otherwise it will get dummy regulator even this buck
doesn't register.as regulator.

BR,
Andrew-sh.Cheng