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

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Message-ID: <aXoF4zi4SZrXaku5@smile.fi.intel.com>
Date: Wed, 28 Jan 2026 14:49:39 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: 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 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.

-- 
With Best Regards,
Andy Shevchenko