linux-kernel - Re: [PATCH 2/3] dt-bindings: pinctrl: rockchip: Add io domain properties

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Date:   Wed, 6 Sep 2023 12:19:09 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Quentin Schulz <quentin.schulz@...obroma-systems.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        linux-rockchip@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-gpio@...r.kernel.org,
        kernel@...gutronix.de,
        Michael Riesch <michael.riesch@...fvision.net>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>
Subject: Re: [PATCH 2/3] dt-bindings: pinctrl: rockchip: Add io domain
 properties

On Wed, Sep 06, 2023 at 10:20:26AM +0200, Quentin Schulz wrote:
> Sascha, Robin,
> 
> On 9/5/23 11:03, Robin Murphy wrote:
> > [You don't often get email from robin.murphy@....com. Learn why this is
> > important at https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > > +        type: boolean
> > > +        description:
> > > +          If true assume that the io domain needed for this pin
> > > group has been
> > > +          configured correctly by the bootloader. This is needed to
> > > break cyclic
> > > +          dependencies introduced when a io domain needs a
> > > regulator that can be
> > > +          accessed through pins configured here.
> > 
> > This is describing a Linux implementation detail, not the binding
> > itself. There's no technical reason a DT consumer couldn't already
> > figure this much out from the existing topology (by observing that the
> > pinctrl consumer is a grandparent of the I/O domain's supply).
> > 
> 
> I am guessing you're suggesting to have some complex handling in the driver
> to detect those cyclic dependencies and ignore the IO domain dependency for
> the pinctrl pins where this happens?

I haven't read this as a suggestion, but only as an argument to make it
clear that I should describe the binding rather than anticipating
how it should be used.

I may have misunderstood it though.

> One of the issues we're having here too is that we lose granularity. There
> are multiple domains inside an IO domain device and here we make the whole
> pinctrl device depend on all domains from one IO domain device (there can be
> multiple ones) while it is factually (on the HW level) only dependent on one
> domain. Considering (if I remember correctly) Heiko highly suggested we
> think about adding child nodes to the IO domain devices to have a DT node
> per domain in the IO domain device, how would this work with the suggested
> DT binding?

I started implementing that. I have moved the IO domains into subnodes
of the IO domain controller and started adding phandles from the pin
groups in rk3568-pinctrl.dtsi to the corresponding IO domains. After a
couple of hours I had phandles for around a quarter of the existing
groups of only one SoC, so doing this for all SoCs would really be a
cumbersome job.

In the end I realized this doesn't solve any problem. Also adding the
properties I suggested doesn't prevent us from adding the more specific
dependencies from the pins to their actual IO domains later.

Sascha

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