linux-kernel - Re: [PATCH v3 1/2] dt-bindings: usb: Add binding for ChromeOS Pogo pin keyboard connector

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Message-ID: <CAE-0n53Q=HFtZqgTNN2iq-XEaedr2zMJ63=k5+Rn3PsOf69fiQ@mail.gmail.com>
Date: Fri, 14 Feb 2025 20:54:11 -0800
From: Stephen Boyd <swboyd@...omium.org>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Konrad Dybcio <konradybcio@...nel.org>, Bjorn Andersson <andersson@...nel.org>, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	patches@...ts.linux.dev, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Benson Leung <bleung@...omium.org>, devicetree@...r.kernel.org, 
	chrome-platform@...ts.linux.dev, Pin-yen Lin <treapking@...omium.org>
Subject: Re: [PATCH v3 1/2] dt-bindings: usb: Add binding for ChromeOS Pogo
 pin keyboard connector

Quoting Krzysztof Kozlowski (2025-02-13 00:11:25)
> On Mon, Feb 10, 2025 at 02:57:11PM -0800, Stephen Boyd wrote:
> > +    const: 1
> > +
> > +  '#size-cells':
> > +    const: 0
> > +
> > +  port:
> > +    $ref: /schemas/graph.yaml#/properties/port
> > +    description: Connection to USB2 port providing USB HS signals
> > +    required:
> > +      - endpoint
> > +
> > +patternProperties:
> > +  "^keyboard@[0-9a-f]{1,2}$":
>
> What does the unit address represent here? Why this isn't just
> "keyboard"? One connector usually has only one keyboard, right?

Yes one connector has one keyboard.

>
> Maybe it is only to fulfill the usb-device schema? The reg is there to
> represent USB hub or controller port, which is not true here.

Right, this is to fulfill the schema. These pins are connected to a USB
hub or controller port, so we use that as the unit address.

>
> I don't have any idea how to solve it. I assume you need the keyboard
> child, right?

Yes we need the keyboard child so that we can make sure the keyboard
that's expected is plugged in instead of some other one that doesn't
pair with the device. We treat the detachable keyboard as 'not external'
or 'expected' when it matches this VID/PID we have listed in DT so that
we trust it slightly more than a standard USB keyboard that you could
plug in to a USB connector.