linux-kernel - Re: [RFC PATCH v2 01/17] OPP: Allow to request stub voltage regulators

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Date:   Mon, 22 Oct 2018 15:12:08 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        linux-tegra@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 01/17] OPP: Allow to request stub voltage
 regulators

On 10/22/18 2:32 PM, Viresh Kumar wrote:
> On 22-10-18, 14:29, Dmitry Osipenko wrote:
>> On 10/22/18 8:36 AM, Viresh Kumar wrote:
>>> On 21-10-18, 23:54, Dmitry Osipenko wrote:
>>>> Voltage regulators may be not available on some variations of HW, allow to
>>>> request stub voltage regulators by OPP core in a such case to reduce code
>>>> churning within drivers.
>>>>
>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>> ---
>>>>  drivers/cpufreq/cpufreq-dt.c | 2 +-
>>>>  drivers/cpufreq/ti-cpufreq.c | 3 ++-
>>>>  drivers/opp/core.c           | 9 +++++++--
>>>>  include/linux/pm_opp.h       | 4 ++--
>>>>  4 files changed, 12 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
>>>> index e58bfcb1169e..6ebca472ec76 100644
>>>> --- a/drivers/cpufreq/cpufreq-dt.c
>>>> +++ b/drivers/cpufreq/cpufreq-dt.c
>>>> @@ -196,7 +196,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
>>>>  	 */
>>>>  	name = find_supply_name(cpu_dev);
>>>>  	if (name) {
>>>> -		opp_table = dev_pm_opp_set_regulators(cpu_dev, &name, 1);
>>>> +		opp_table = dev_pm_opp_set_regulators(cpu_dev, &name, 1, false);
>>>>  		if (IS_ERR(opp_table)) {
>>>>  			ret = PTR_ERR(opp_table);
>>>>  			dev_err(cpu_dev, "Failed to set regulator for cpu%d: %d\n",
>>>
>>> Have you actually tested this stuff ? The cpufreq-dt driver will
>>> probably fail to probe if the CPU node has a "-supply" property, but
>>> no regulator matching that.
>>>
>>
>> Please notice that this patch doesn't change the original behaviour
>> and I suppose that failing in a case of missing regulator is the
>> expected behaviour for cpufreq-dt. Hence can't see any problem here.
> 
> So why have this patch then ?

Because there is one Tegra20 board (tegra20-trimslice) that doesn't declare necessary regulators, but we want to have CPU frequency scaling. I couldn't find board schematics and so don't know if CPU / CORE voltages are fixed on Trim-Slice or it is just preferable not to have DVFS for that board, it is an outlet-powered device [0]. Hence tegra20-cpufreq driver will request a dummy regulators when appropriate. 

[0] http://www.compulab.co.il/utilite-computer/web/trim-slice