linux-kernel - Re: [PATCH RFC] dt-bindings: pinctrl: support specifying pins

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Date:   Thu, 11 Nov 2021 16:31:28 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Rafał Miłecki <zajec5@...il.com>,
        ext Tony Lindgren <tony@...mide.com>
Cc:     Rob Herring <robh+dt@...nel.org>, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH RFC] dt-bindings: pinctrl: support specifying pins

On Thu, Nov 11, 2021 at 12:14 AM Rafał Miłecki <zajec5@...il.com> wrote:

> While working with pinctrl in Linux I started wondering if we could
> start specifying pins in DT instead of Linux drivers. When working with
> DT we usually avoid hardcoding hardware description in drivers so it
> isn't clear to me why it doesn't apply to pins.

Historically this is what pinctrl-single.c does.
Documentation/devicetree/bindings/pinctrl/pinctrl-single.txt

At the time we created pin control there was a bit back-and-forth and
the conclusion was that there is not one-size-fits all for pin defines.

The reason TI (Tony) wanted to push the information into DT
was that what he gets is a number of unprocessed ASIC datasets,
that are then turned into tables with a script. Header files or DTS
source alike, but some kind of tables.

At the time (2011?) it was unclear what kind of data should go into
e.g. header and data files in the kernel (modules) and what should
go into the DT. So the approach to put pin information into the DT
was allowed for pinctrl-single.

The way I have understood it, DT maintainers have since gotten
a bit wary about (ab)using the DT as a container for "anything data"
and prefer that drivers contain details and derive these from
compatible strings.

As of today, IIUC the DT maintainers are against this scheme.

That said, the topic is open in a way. Some people are also annoyed
that some graphics drivers just ask Torvalds to pull 100.000+ lines
of register defnes in some merge windows. The data has to go
somewhere.

Yours,
Linus Walleij