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

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Date:   Tue, 13 Mar 2018 10:20:52 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Peter De Schrijver <pdeschrijver@...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 13/03/18 09:51, Peter De Schrijver wrote:
> On Mon, Mar 12, 2018 at 12:15:22PM +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);
>>>  }
>>
>> OK, so this bit does not make sense to me. In the above we are switching
>> from the DFLL to the PLL (ie. disabling the DFLL) and so to ensure we
>> are operating at the correct voltage after disabling the DFLL we need to
>> sync the voltage. Seems we would need to do this for all devices, no?
>> How is the different between Tegra124 and Tegra210?
> 
> Yes. So in case of i2c the regulator framework will reapply the voltage it
> knows which in our case is the boot voltage for VDD_CPU because noone else
> from a regulator framework pov has ever changed the voltage. In case of PWM
> putting the PWM output pad in tri state will cause the OVR regulator to output
> a hardware defined voltage. This is done as part of the dfll_clk_disable()
> function. To summarize:

So this is the piece of information I was missing. Maybe add this to the
changelog so it is clear why we do not need to handle the cpu rail in
the case of PWM.

Cheers
Jon

-- 
nvpublic