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

[Konrad Dybcio]

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 at quicinc.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?

Konrad