linux-kernel - Re: [PATCH v2 3/5] devfreq: rk3399_dmc: Pass ODT and auto power down parameters to TF-A.

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Message-ID: <20190320220223.GP112750@google.com>
Date:   Wed, 20 Mar 2019 15:02:23 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Gaël PORTAY <gael.portay@...labora.com>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        Derek Basehore <dbasehore@...omium.org>,
        Heiko Stuebner <heiko@...ech.de>, linux-pm@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Rob Herring <robh+dt@...nel.org>, linux-kernel@...r.kernel.org,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Klaus Goger <klaus.goger@...obroma-systems.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-rockchip@...ts.infradead.org, Randy Li <ayaka@...lik.info>,
        kernel@...labora.com, linux-arm-kernel@...ts.infradead.org,
        Lin Huang <hl@...k-chips.com>
Subject: Re: [PATCH v2 3/5] devfreq: rk3399_dmc: Pass ODT and auto power down
 parameters to TF-A.

Hi Gaël,

On Wed, Mar 20, 2019 at 05:50:13PM -0400, Gaël PORTAY wrote:
> Hi Matthias,
> 
> On Tue, Mar 19, 2019 at 05:33:52PM -0700, Matthias Kaehlcke wrote:
> > ...
> > > @@ -95,6 +103,19 @@ static int rk3399_dmcfreq_target(struct device *dev, unsigned long *freq,
> > >  
> > >  	mutex_lock(&dmcfreq->lock);
> > >  
> > > +	if (target_rate >= dmcfreq->odt_dis_freq)
> > > +		odt_enable = true;
> > > +
> > > +	/*
> > > +	 * This makes a SMC call to the TF-A to set the DDR PD (power-down)
> > > +	 * timings and to enable or disable the ODT (on-die termination)
> > > +	 * resistors.
> > > +	 */
> > > +	arm_smccc_smc(ROCKCHIP_SIP_DRAM_FREQ, dmcfreq->odt_pd_arg0,
> > > +		      dmcfreq->odt_pd_arg1,
> > > +		      ROCKCHIP_SIP_CONFIG_DRAM_SET_ODT_PD,
> > > +		      odt_enable, 0, 0, 0, &res);
> > 
> > Is it necessary/desirable to make this call for every frequency
> > change? IIUC it should be only needed when odt_enable changes and the
> > driver could track the state. If the DDR frequency doesn't change too
> > often and the overhead of the call is small it shouldn't be really
> > important though.
> >
> 
> I will test your solution first to make sure there is no regression to
> run that call for frequency change only.

If there is no frequency change the function returns at the
beginning. My suggestion was to only do the call when 'odt_enable'
changes, i.e. when a change (up or down) passes the 'odt_dis_freq'
threshold.

> Also, the call takes around 300us.

Thanks for the info!

Matthias