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

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Message-ID: <aXp05Dk7gGc5DkPt@smile.fi.intel.com>
Date: Wed, 28 Jan 2026 22:43:16 +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 08:52:50PM +0100, Krzysztof Kozlowski wrote:
> On 28/01/2026 17:05, Andy Shevchenko wrote:
> > On Wed, Jan 28, 2026 at 04:48:18PM +0100, Krzysztof Kozlowski wrote:
> >> On 28/01/2026 13:49, 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:

...

> >>>> 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.
> >>
> >> What is inconsistent exactly? What sort of rule tells that every little
> >> function needs a device node? It's first time I hear about any of such
> >> rule and for all this time we already NAKed it so many times (node per
> >> GPIO, node per clock, node per every little pin).
> > 
> > That we should represent the HW as is. There is no "rule", there is a common
> > sense. Of course, it's possible to have all-in-one node, but this may lead
> > to a disaster when there are tons of devices in the Multi Functional HW
> > and some of them use the same properties. How would you distinguish HW
> > with two GPIO banks, two I²C controllers, et cetera? That's what my common
> 
> I do not see problems in these examples. GPIO banks have gpio-cells for
> that. i2c controllers are busses, so as I explained in other email, must
> have their own node whenever any other node is expected.
> 
> And for everything which is more complex, e.g. regulators, we do expect
> child nodes.
> 
> Still the "MFD" is not a reason itself, we consistently give such review
> and we also documented it.
> 
> > sense tells to me, putting all eggs into one bucket is just a mine field
> > for the future.
> 
> Some years passed and I do not remember any mine happening here.
> Actually mines appeared when people DID create fake nodes, because then
> when the actual true bus node was needed it was violating the rule we
> have - not mixing bus and non-bus nodes on the same level.

Okay, thanks for elaboration. I definitely learnt something new about DT.

-- 
With Best Regards,
Andy Shevchenko