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

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Message-ID: <aKhge2ngLwj4uhmC@linaro.org>
Date: Fri, 22 Aug 2025 14:20:11 +0200
From: Stephan Gerhold <stephan.gerhold@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: 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>,
	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 Fri, Aug 22, 2025 at 02:57:24PM +0300, Dmitry Baryshkov wrote:
> On Fri, Aug 22, 2025 at 01:45:38PM +0200, Stephan Gerhold wrote:
> > On Fri, Aug 22, 2025 at 02:01:30PM +0300, Dmitry Baryshkov wrote:
> > > On Thu, Aug 21, 2025 at 03:53:28PM +0200, Neil Armstrong wrote:
> > > > The Thinkpad T14s embeds a transparent 4lanes DP->HDMI transceiver
> > > > connected to the third QMP Combo PHY 4 lanes.
> > > > 
> > > > Add all the data routing, disable mode switching and specify the
> > > > QMP Combo PHY should be in DP-Only mode to route the 4 lanes to
> > > > the underlying DP phy.
> > > > 
> > > > Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> > > > ---
> > > >  .../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
> > > > @@ -62,6 +62,20 @@ switch-lid {
> > > >  		};
> > > >  	};
> > > >  
> > > > +
> > > > +	hdmi-connector {
> > > > +		compatible = "hdmi-connector";
> > > > +		type = "a";
> > > > +		pinctrl-0 = <&hdmi_hpd_default>;
> > > > +		pinctrl-names = "default";
> > > [...]
> > > > +
> > > > +		port {
> > > > +			hdmi_con: endpoint {
> > > > +				remote-endpoint = <&usb_1_ss2_qmpphy_out>;
> > > 
> > > Please describe the transparent bridge too. It can be covered by the
> > > simple-bridge.yaml / simple-bridge.c
> > > 
> > 
> > I think this isn't the case here(?), but how are we going to handle
> > devices where we don't know which bridge chip is used? I've seen at
> > least 3 or 4 different chips already across all X1E laptops and we don't
> > have schematics for most of them.
> 
> Open the case, inspect the board, identify the chip. Everything is as
> usual.
> 

The chip might not have any visible identifier. :-) But I guess there is
no point theorizing about such potential issues now. We'll see. I agree
it would be cleaner to have the bridges modelled.

Thanks,
Stephan