linux-kernel - Re: [PATCH v3 09/11] cpufreq: tegra124-cpufreq: extend to support Tegra210

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Message-ID: <20180309081438.GO6190@tbergstrom-lnx.Nvidia.com>
Date:   Fri, 9 Mar 2018 10:14:38 +0200
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Jon Hunter <jonathanh@...dia.com>
CC:     <linux-tegra@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <mturquette@...libre.com>, <sboyd@...eaurora.org>,
        <robh+dt@...nel.org>, <mark.rutland@....com>,
        <devicetree@...r.kernel.org>, <lgirdwood@...il.com>,
        <broonie@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 09/11] cpufreq: tegra124-cpufreq: extend to support
 Tegra210

On Thu, Mar 08, 2018 at 11:25:04PM +0000, Jon Hunter wrote:
> 
> On 06/02/18 16:34, Peter De Schrijver wrote:
> > Tegra210 has a very similar CPU clocking scheme than Tegra124. So add
> > support in this driver. Also allow for the case where the CPU voltage is
> > controlled directly by the DFLL rather than by a separate regulator object.
> > 
> > Signed-off-by: Peter De Schrijver <pdeschrijver@...dia.com>
> > ---
> >  drivers/cpufreq/tegra124-cpufreq.c | 15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/cpufreq/tegra124-cpufreq.c b/drivers/cpufreq/tegra124-cpufreq.c
> > index 4353025..f8e01a8 100644
> > --- a/drivers/cpufreq/tegra124-cpufreq.c
> > +++ b/drivers/cpufreq/tegra124-cpufreq.c
> > @@ -64,7 +64,8 @@ static void tegra124_cpu_switch_to_pllx(struct tegra124_cpufreq_priv *priv)
> >  {
> >  	clk_set_parent(priv->cpu_clk, priv->pllp_clk);
> >  	clk_disable_unprepare(priv->dfll_clk);
> > -	regulator_sync_voltage(priv->vdd_cpu_reg);
> > +	if (priv->vdd_cpu_reg)
> > +		regulator_sync_voltage(priv->vdd_cpu_reg);
> >  	clk_set_parent(priv->cpu_clk, priv->pllx_clk);
> >  }
> >  
> > @@ -89,10 +90,10 @@ static int tegra124_cpufreq_probe(struct platform_device *pdev)
> >  		return -ENODEV;
> >  
> >  	priv->vdd_cpu_reg = regulator_get(cpu_dev, "vdd-cpu");
> > -	if (IS_ERR(priv->vdd_cpu_reg)) {
> > -		ret = PTR_ERR(priv->vdd_cpu_reg);
> > -		goto out_put_np;
> > -	}
> > +	if (IS_ERR(priv->vdd_cpu_reg) != -EPROBE_DEFER)
> > +		priv->vdd_cpu_reg = NULL;
> > +	else
> > +		return -EPROBE_DEFER;
> 
> I am still not sure that we should rely on the fact that the regulator
> is not present in DT to imply that we do not need it. I think that we
> should be checking if we are using I2C mode here.
> 

The cpufreq driver doesn't know this however. Also the current approach of
setting the same voltage when switching to pll_x is incorrect. The CVB
tables when using pll_x include more margin than when using the DFLL.

Peter.