linux-kernel - Re: [PATCH v2] dt: arm64: qcom: sc8280xp-x13s: amend usb0-sbu-mux enable gpio

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Message-ID: <64d963bd-b38c-4f14-bb1d-f7e89dad999a@oldschoolsolutions.biz>
Date: Wed, 11 Jun 2025 21:25:20 +0200
From: Jens Glathe <jens.glathe@...schoolsolutions.biz>
To: Johan Hovold <johan@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 Johan Hovold <johan+linaro@...nel.org>
Subject: Re: [PATCH v2] dt: arm64: qcom: sc8280xp-x13s: amend usb0-sbu-mux
 enable gpio


On 6/10/25 09:31, Johan Hovold wrote:
> On Tue, Jun 10, 2025 at 07:04:46AM +0200, Jens Glathe via B4 Relay wrote:
> DP alt mode works on both ports of the X13s and "resulted in
> gpio165" makes little sense so this commit message would need to be
> extended.

Well, that was the problem. It didn't on USB0. without and with the 4 
lanes patch.

Observed on Windows Dev Kit 2023 and X13s, what prompted me to look deeper.

> GPIO 101 *is* the OE_N pin, while GPIO 165 is not even connected
> according to the schematics. The mux may still work after this change,
> but you'd be relying on it having been enabled by the boot firmware.
>
Schematics trump any other data, of course. After a lot of tests and 
some wild
results I could narrow it down to the display I used for testing, iiyama 
XUB2792QSN.
It works with HDMI adapters on ~all other displays I have - with and 
without any
4-lanes, lttpr patches. And the original GPIO. The issue with the 
display appears to
be something linked to how negotiation is done by it on that specific port.

Do I need to do anything since its already NAK?

with best regards

Jens