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 16:46:11 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Laxman Dewangan <ldewangan@...dia.com>
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 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.

Yours,
Linus Walleij