linux-kernel - Re: [PATCH 2/2] arm64: dts: qcom: x1p42100-lenovo-thinkbook-16: add hdmi bridge with enable pin

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Message-ID: <8b562354-1c6f-4b13-be55-b23a6a93d9be@oldschoolsolutions.biz>
Date: Sat, 20 Dec 2025 21:17:16 +0100
From: Jens Glathe <jens.glathe@...schoolsolutions.biz>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
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,
 Val Packett <val@...kett.cool>
Subject: Re: [PATCH 2/2] arm64: dts: qcom: x1p42100-lenovo-thinkbook-16: add
 hdmi bridge with enable pin

On 20.12.25 19:52, Dmitry Baryshkov wrote:
> On Sat, Dec 20, 2025 at 06:47:10PM +0100, Jens Glathe via B4 Relay wrote:
>> From: Jens Glathe <jens.glathe@...schoolsolutions.biz>
>>
>> Add TLMM 119 for hdmi bridge enable. AeoB has this gpio.
> Whaat is AeoB? I don't see the GPIO being used in other place.

AeoB is a resource format used by the QCom Windows drivers to add / 
overwrite definitions coming from the ACPI tables. [1] It had the info 
that was not to be found in the DSDT. Actually, x1e80100.dtsi has the 
edp0_hpd_default pinctrl which is required for the display to work with 
the function edp_hot. I verified this, you need both. I can use that 
definition in this patchset, too, but its not for HDMI.

[1]: 
https://github.com/alexVinarskis/qcom-aeob-dumps/tree/master/lenovo-thinkbook-16-g7-qoy

>> In general this is the same setup as on the T14s. Since its using simple-bridge
>> and also is Lenovo, we also use the same realtek,rtd2171 compatible.
>> The real chip identity is not known yet. The bridge is wired with un-swapped
>> lanes, though.
> Is the chip marked anyhow?
I don't know. Haven't looked inside.
>> As for gpio119 being used twice: It doesn't work if you don't, so it may be a case
>> of TLMM multiplexing hpd for both ports.
> What is the relationship between enable and HPD?

Yeah, good question. Actually HDMI hpd is wired to gpio126, and works 
without the enable pin. But no link training succeeds, no display coming 
up. With enable set on probe() this works. If you have the lane order 
right. The HDMI socket  is "above" the type-c ports on the TB16, 
compared to the T14s where it is "below" the type-c ports, so swapped 
lanes sounds reasonable.

[...]