linux-kernel - Re: [PATCH 6/8] PM / OPP: Support adjusting OPP voltages at runtime

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Message-ID: <1564371555.18434.11.camel@mtksdaap41>
Date:   Mon, 29 Jul 2019 11:39:15 +0800
From:   Roger Lu <roger.lu@...iatek.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>
CC:     Andrew-sh Cheng (鄭式勳) 
        <andrew-sh.cheng@...iatek.com>,
        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>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        srv_heupstream <srv_heupstream@...iatek.com>,
        Fan Chen (陳凡) 
        <fan.chen@...iatek.com>, <yt.lee@...iatek.com>
Subject: Re: [PATCH 6/8] PM / OPP: Support adjusting OPP voltages at runtime

Dear Stephen Boyd,

This patch is derived from [1]. Please kindly shares the suggestion to
us. Thanks very much.

[1]: https://lore.kernel.org/patchwork/patch/599279/

Dear Viresh,

I followed _opp_set_availability() coding style to refine
dev_pm_opp_adjust_voltage() from this patch. Is this refinement suitable
for OPP core? Thanks a lot.

On Mon, 2019-05-20 at 12:47 +0800, Viresh Kumar wrote:
> On 16-05-19, 17:08, Andrew-sh.Cheng wrote:
> > From: Stephen Boyd <sboyd@...eaurora.org>
> > 
> > On some SoCs the Adaptive Voltage Scaling (AVS) technique is
> > employed to optimize the operating voltage of a device. At a
> > given frequency, the hardware monitors dynamic factors and either
> > makes a suggestion for how much to adjust a voltage for the
> > current frequency, or it automatically adjusts the voltage
> > without software intervention. Add an API to the OPP library for
> > the former case, so that AVS type devices can update the voltages
> > for an OPP when the hardware determines the voltage should
> > change. The assumption is that drivers like CPUfreq or devfreq
> > will register for the OPP notifiers and adjust the voltage
> > according to suggestions that AVS makes.
> > 
> > This patch is devired from [1] submitted by Stephen.
> > [1] https://lore.kernel.org/patchwork/patch/599279/
> > 
> > Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> > Signed-off-by: Roger Lu <roger.lu@...iatek.com>
> > ---
> >  drivers/opp/core.c     | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/pm_opp.h | 11 +++++++
> >  2 files changed, 89 insertions(+)
> 
> This is an rcu implementation which got removed long back from OPP core. Please
> align this with the latest changes.
> 


/**
 * dev_pm_opp_adjust_voltage() - helper to change the voltage of an OPP
 * @dev:		device for which we do this operation
 * @freq:		OPP frequency to adjust voltage of
 * @u_volt:		new OPP voltage
 *
 * Return: -EINVAL for bad pointers, -ENOMEM if no memory available for
the
 * copy operation, returns 0 if no modifcation was done OR modification
was
 * successful.
 */
int dev_pm_opp_adjust_voltage(struct device *dev, unsigned long freq,
			      unsigned long u_volt)
{
	struct opp_table *opp_table;
	struct dev_pm_opp *tmp_opp, *opp = ERR_PTR(-ENODEV);
	int r = 0;

	/* Find the opp_table */
	opp_table = _find_opp_table(dev);
	if (IS_ERR(opp_table)) {
		r = PTR_ERR(opp_table);
		dev_warn(dev, "%s: Device OPP not found (%d)\n", __func__, r);
		return r;
	}

	mutex_lock(&opp_table->lock);

	/* Do we have the frequency? */
	list_for_each_entry(tmp_opp, &opp_table->opp_list, node) {
		if (tmp_opp->rate == freq) {
			opp = tmp_opp;
			break;
		}
	}

	if (IS_ERR(opp)) {
		r = PTR_ERR(opp);
		goto adjust_unlock;
	}

	/* Is update really needed? */
	if (opp->supplies->u_volt == u_volt)
		goto adjust_unlock;

	opp->supplies->u_volt = u_volt;

	dev_pm_opp_get(opp);
	mutex_unlock(&opp_table->lock);

	/* Notify the voltage change of the OPP */
	blocking_notifier_call_chain(&opp_table->head,
OPP_EVENT_ADJUST_VOLTAGE,
				     opp);

	dev_pm_opp_put(opp);
	goto adjust_put_table;

adjust_unlock:
	mutex_unlock(&opp_table->lock);
adjust_put_table:
	dev_pm_opp_put_opp_table(opp_table);
	return r;
}

Sincerely,
Roger Lu.