linux-kernel - Re: [PATCH v13 1/3] dt-bindings: i2c: Add CP2112 HID USB to SMBus Bridge

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Message-ID: <20260128-pelican-silenced-cd6a5bf69672@spud>
Date: Wed, 28 Jan 2026 15:06:58 +0000
From: Conor Dooley <conor@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
	Danny Kaehn <danny.kaehn@...xus.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Benjamin Tissoires <bentiss@...nel.org>,
	Andi Shyti <andi.shyti@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Jiri Kosina <jikos@...nel.org>,
	devicetree@...r.kernel.org, linux-input@...r.kernel.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Ethan Twardy <ethan.twardy@...xus.com>, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, Leo Huang <leohu@...dia.com>,
	Arun D Patil <arundp@...dia.com>, Willie Thai <wthai@...dia.com>,
	Ting-Kai Chen <tingkaic@...dia.com>
Subject: Re: [PATCH v13 1/3] dt-bindings: i2c: Add CP2112 HID USB to SMBus
 Bridge

On Wed, Jan 28, 2026 at 02:49:39PM +0200, Andy Shevchenko wrote:
> On Wed, Jan 28, 2026 at 11:35:25AM +0100, Krzysztof Kozlowski wrote:
> > On Tue, Jan 27, 2026 at 10:02:17AM -0600, Danny Kaehn wrote:
> > > On Tue, Jan 27, 2026 at 08:47:48AM -0600, Danny Kaehn wrote:
> > > > This is a USB HID device which includes an I2C controller and 8 GPIO pins.
> > > > 
> > > > The binding allows describing the chip's gpio and i2c controller in DT,
> > > > with the i2c controller being bound to a subnode named "i2c". This is
> > > > intended to be used in configurations where the CP2112 is permanently
> > > > connected in hardware.
> > > > 
> > > > Signed-off-by: Danny Kaehn <danny.kaehn@...xus.com>
> > > > ---
> > > 
> > > Hi Folks (Intended for Rob or Krzysztof),
> > > 
> > > Wasn't sure the best way to go about this, but trying to see the best
> > > way to get a message in front of you regarding an ask from Andy S.
> > > 
> > > In [1], Rob H initially directed that the gpio chip share a node with
> > > the CP2112 itself, rather than having a subnode named 'gpio'.
> > > 
> > > Initially, I did the same thing for both DT and ACPI, but Andy S.
> > > directed that ACPI should not have the node be shared in that way.
> > > 
> > > With the last revision of this patch, Andy S. asked that I try to get a
> > > rationalle from Rob (or other DT expert presumably) on why the gpio node
> > > should be combined with the parent, rather than being a named subnode
> > > [2].
> > 
> > Because it is explicitly asked in writing bindings. Please read it.
> > 
> > Because we do not want Linux driver model affecting design of bindings
> > and DTS, by subnodes present only to instantiate Linux drivers. I do not
> > care about driver model in this review and I do not see any reason it
> > should make DTS less obvious or readable.
> > 
> > That's actually rule communicated many times, also documented in writing
> > bindings and in recent talks.
> 
> Does DT represents HW in this case? Shouldn't I²C controller be the same node?
> Why not? This is inconsistent for the device that is multi-functional. And from
> my understanding the firmware description (DT, ACPI, you-name-it) must follow
> the HW. I don't see how it's done in this case.

The i2c controller should probably be in the same node too, unless it
would cause conflicts between function (e.g. inability to figure out if
a child is a hog or a i2c device). I would like a rationale provided for
why the i2c controller is in a subnode.

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