linux-kernel - Re: [PATCH 7/7] pinctrl: tegra: Add driver to configure voltage and power state of io pads

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Message-ID: <571F89E3.1040907@wwwdotorg.org>
Date:	Tue, 26 Apr 2016 09:31:47 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Laxman Dewangan <ldewangan@...dia.com>,
	Linus Walleij <linus.walleij@...aro.org>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Jon Hunter <jonathanh@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH 7/7] pinctrl: tegra: Add driver to configure voltage and
 power state of io pads

On 04/26/2016 07:32 AM, Laxman Dewangan wrote:
>
> On Friday 15 April 2016 05:17 PM, Laxman Dewangan wrote:
>>
>> On Friday 15 April 2016 04:45 PM, Linus Walleij wrote:
>>> On Fri, Apr 15, 2016 at 11:55 AM, Laxman Dewangan
>>> <ldewangan@...dia.com> wrote:
>>>> On Friday 15 April 2016 02:55 PM, Linus Walleij wrote:
>>>>> If the pin could actually set a voltage level it would have a
>>>>> regulator.
>>>>> I don't believe that. I think it is selecting one of two rails which
>>>>> could theoretically hold two totally different voltages.
>>>>>
>>>>> And that is what power-source is about.
>>>> The IO rails connected to PMIC rail and connection does not get change.
>>>> We change the voltage of PMIC rails via regulator calls. And then
>>>> configure
>>>> pads for the new voltage.
>>> Aha I get it! So you adjust something in the I/O-cell so that it is
>>> adapted
>>> for the new voltage.
>>>
>>> OK that seems to be something new. I suspect
>>> power-voltage-select = <n>; where N i in uV would solve this?
>>> (We should use uV since regulators use this.)
>>
>> Thanks for new property. I will make the unit and type same as the
>> regulator framework.
>
> We have the ops for configuring the pin config as
>
>          int (*pin_config_group_set) (struct pinctrl_dev *pctldev,
>                                       unsigned selector,
>                                       unsigned long *configs,
>                                       unsigned num_configs);
>
>
> The config is 32 bit, upper 16 for config argument and  and lower 16 for
> the config param.
>
> So we can not accommodate 3300000uV until we change it to mV i.e. 3300mV.
>
> So on interface, we can read uV from DT but when making config, we can
> translate it to mV before passing to pin_config_group_set.

A SoC-specific enum would make more sense. It would avoid any 
translation. There's no need for a generic value since the available set 
of options is SoC-specific, the data source is SoC-specific, and there's 
no need for any code besides the SoC-specific driver to interpret the 
value in any way at all.