linux-kernel - Re: [PATCH 2/2] pinctrl: tegra: Add driver to configure voltage and power of io pads

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Date:   Tue, 8 Nov 2016 21:18:54 +0530
From:   Laxman Dewangan <ldewangan@...dia.com>
To:     Linus Walleij <linus.walleij@...aro.org>
CC:     "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Stephen Warren <swarren@...dotorg.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jon Hunter <jonathanh@...dia.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] pinctrl: tegra: Add driver to configure voltage and
 power of io pads


On Tuesday 08 November 2016 09:16 PM, Linus Walleij wrote:
> On Tue, Nov 8, 2016 at 2:35 PM, Laxman Dewangan <ldewangan@...dia.com> wrote:
>
>> There is two types of configuration in given platform, the IO voltage does
>> not get change (fixed in given platform) and in some of cases, get change
>> dynamically like SDIO3.0 where the voltage switches to 3.3V and 1.8V.
>>
>> Yes, it can be integrated with the regulator handle and then it can call the
>> required configurations through notifier and regulator_get_voltage().
>> But I think it is too much complex for the static configurations. This
>> mandate also to populate the regulator handle and all power tree.
>>
>> The simple way for static configuration (case where voltage does not get
>> change), just take the power tree IO voltage from DT and configure the IO
>> pad control register.
>>
>> For dynamic case, there is some sequence need to be followed based on
>> voltage direction change (towards lower or towards higher) for the voltage
>> change and the IO pad voltage configuration and it is simple to do it from
>> client driver.
> The devicetree should describe the platform.
>
> Adding this custom attribute does not describe the platform very
> well since the dependency to the corresponding regulator is hidden.
>
> The point of device tree is not as much to make things simple as
> to describe the world properly.
>
> So to me it is simple: use regulators and phandles.
>
> It might require a bit of upfront coding but the result will look
> much nicer.

Oops, I asked same clarification when replying the Thierry's comment.

Got answer now.. only via regulator support.


I am going to support the IO pad voltage control with regulator only.
No custom attribute for this.
However, for support for low-power will be same as this patch.