linux-kernel - Re: [PATCH RFC 3/3] arm64: dts: qcom: x1e78100-lenovo-thinkpad-t14s: add HDMI nodes

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Message-ID: <9923f086-9deb-4d3f-813c-7d9b94c7dfdb@oss.qualcomm.com>
Date: Mon, 8 Sep 2025 09:17:20 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Jens Glathe <jens.glathe@...schoolsolutions.biz>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 3/3] arm64: dts: qcom: x1e78100-lenovo-thinkpad-t14s:
 add HDMI nodes

On 9/8/25 9:16 AM, Konrad Dybcio wrote:
> On 9/6/25 10:41 AM, Jens Glathe wrote:
>> On 21.08.25 15:53, Neil Armstrong wrote:
>>> The Thinkpad T14s embeds a transparent 4lanes DP->HDMI transceiver
>>> connected to the third QMP Combo PHY 4 lanes.
>>>
>> [...]
>>>   .../dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi    | 44 ++++++++++++++++++++++
>>>   1 file changed, 44 insertions(+)
>> [...]
>>> diff --git a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
>>> index 4cf61c2a34e31233b1adc93332bcabef22de3f86..5b62b8c3123633360f249e3ecdc8ea23f44e8e09 100644
>>> --- a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
>>> +++ b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
>> [...]
>>> +&mdss_dp2 {
>>> +    status = "okay";
>>> +};
>>> +
>>> +&mdss_dp2_out {
>>> +    data-lanes = <0 1 2 3>;
>>> +};
>>> +
>>
>> Hi Neil,
>>
>> shouldn't mdss_dp2_out also have the link-frequencies property?
>>
>> +    link-frequencies = /bits/ 64 <1620000000 2700000000 5400000000 8100000000>;
>>
>> Or is it something the bridge already negotiates?
> 
> No, it seems like our driver falls back to HBR2 (54xx) ever since the
> driver has been made aware of this property:
> 
> commit 381518a1677c49742a85f51e8f0e89f4b9b7d297
> Author: Kuogee Hsieh <quic_khsieh@...cinc.com>
> Date:   Tue Dec 27 09:45:02 2022 -0800
> 
>     drm/msm/dp: Add capability to parser and retrieve max DP link supported rate from link-frequencies property of dp_out endpoint
> 
> Dmitry, is there any reason not to allow HBR3 by default? Is our dp
> controller/driver not smart enough not to advertise rates it can't
> support, during negotiation?

I suppose if I want an answer from Dmitry, it would be fair to add
him to the recipient list.. fixing that

Konrad