linux-kernel - Re: [PATCH 1/9] dt-bindings: soc: qcom: eud: Restructure to model multi-path hardware

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Message-ID: <sfazro75vspadpe4wco7zvlalcy2wbrbdjx2wn7lyonjgw22sf@z73u67pinusx>
Date: Mon, 19 Jan 2026 13:58:12 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Elson Serrao <elson.serrao@....qualcomm.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Konrad Dybcio <konradybcio@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Souradeep Chowdhury <quic_schowdhu@...cinc.com>, 
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, linux-usb@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] dt-bindings: soc: qcom: eud: Restructure to model
 multi-path hardware

On Sat, Jan 17, 2026 at 12:57:58PM +0100, Krzysztof Kozlowski wrote:
> On Fri, Jan 16, 2026 at 03:20:58PM -0800, Elson Serrao wrote:
> > The Qualcomm Embedded USB Debugger (EUD) hardware can intercept up to
> > two independent High-Speed UTMI data paths, depending on the SoC
> > configuration. Each path operates independently with:
> > 
> > - Dedicated PHY interface
> > - Distinct USB connector and controller associations
> > - Role dependent routing
> > 
> > Model these hardware paths as separate eud-path nodes to accurately
> > represent the physical topology and add below per-path properties:
> > 
> > phys: EUD exposes a High-Speed debug hub that relies on HS-PHY for its
> > operation. This property references the HS-PHY associated with the UTMI
> > path.
> > 
> > usb-role-switch: Indicates that the USB port on this UTMI path supports
> > role switching. In device role, debug mode inserts the EUD hub into the
> > UTMI path. In host role, the EUD hub is bypassed and UTMI traffic flows
> > directly between the PHY and the USB controller.
> > 
> > This change breaks backwards compatibility, but the previous binding
> > omitted critical resources like PHY and did not describe per-path
> > topology. Without these modifications EUD cannot be guaranteed to
> > function.
> 
> It was working for 3 years, so your guarantees are just imprecise. FUD
> is not an argument.
> 
> Qualcomm task at 2022 was to post complete bindings. These were posted
> and accepted. Three years later you say that previous posting was
> bollocks and this cannot even work?
> 

That is correct. The description of the hardware that was provided when
this was upstreamed and the binding that was accepted based on this
description is wrong.

There's absolutely a value in maintainting backwards compatibility in
general, but is this one of those cases?

> Nah, take responsibility of what you did in the past.
> 

In my view the responsible thing is to accept that we got it wrong and
make sure EUD is enabled end-to-end so people can actually use it.

Regards,
Bjorn