linux-kernel - Re: [PATCH 1/2] arm64: dts: qcom: Enable lvds panel-DV215FHM-R01 for rb3gen2 industrial mezzanine

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Message-ID: <qps5fkbgdqqvoqa3m5l4naksyc4aoq4xqnciyrpkrbs5qcno7c@aa6ync6sk4ju>
Date: Wed, 12 Nov 2025 10:53:36 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Gopi Botlagunta <venkata.botlagunta@....qualcomm.com>, 
	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, 
	venkata.valluru@....qualcomm.com, jessica.zhang@....qualcomm.com, 
	Yi Zhang <zhanyi@....qualcomm.com>
Subject: Re: [PATCH 1/2] arm64: dts: qcom: Enable lvds panel-DV215FHM-R01 for
 rb3gen2 industrial mezzanine

On Wed, Nov 12, 2025 at 05:02:20PM +0200, Dmitry Baryshkov wrote:
> On Wed, Nov 12, 2025 at 08:18:11PM +0530, Gopi Botlagunta wrote:
> > Below is the routing diagram of dsi lanes from qcs6490 soc to
> > mezzanine.
> > 
> > DSI0 --> SW1403.4 --> LT9611uxc --> hdmi port
> >                  |
> >                   --> SW2700.1 --> dsi connector
> >                               |
> >                                --> LT9211c --> LVDS connector
> > 
> > Disable hdmi connector for industrial mezzanine and enable
> > LT9211c bridge and lvds panel node.
> > LT9211c is powered by default with reset gpio connected to 117.
> > 
> > Signed-off-by: Yi Zhang <zhanyi@....qualcomm.com>
> > Signed-off-by: Gopi Botlagunta <venkata.botlagunta@....qualcomm.com>
> > ---
> >  .../qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso | 106 +++++++++++++++++++++
> >  1 file changed, 106 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso b/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso
> > index 619a42b5ef48..cc8ee1643167 100644
> > --- a/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso
> > +++ b/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso
> > @@ -8,6 +8,112 @@
> >  #include <dt-bindings/clock/qcom,gcc-sc7280.h>
> >  #include <dt-bindings/pinctrl/qcom,pmic-gpio.h>
> >  
> > +/ {
> > +
> > +	hdmi-connector {
> > +		status = "disabled";
> > +	};
> > +
> > +	panel_lvds: panel-lvds@0 {
> > +		compatible = "panel-lvds";
> 
> Please describe the actual panel using compatible, etc. It's not that
> this is some generic uknown LVDS panel.
> 

I presume the mezzanine doesn't have a panel, so how do we provide the
description of the mezzanine such that a developer can quickly get up to
speed with their specific panel connected to it?

Do we leave this node disabled, just for reference, or do we specify a
specific panel and then have the developer copy and adopt this to their
panel?

The benefit of doing it like that is that we provide a complete example
and something we can test. But at the same time, If I presume we might
have users of the mezzanine without an attached LVDS panel?

> > +		data-mapping = "vesa-24";
> > +		width-mm = <476>;
> > +		height-mm = <268>;

The way this patch is written we certainly have some specific panel in
mind...

Regards,
Bjorn

> > +
> > +		status = "okay";
> > +
> > +		panel-timing {
> > +			clock-frequency = <148500000>;
> > +			hactive = <1920>;
> > +			vactive = <1080>;
> > +			hfront-porch = <88>;
> > +			hback-porch = <148>;
> > +			hsync-len = <44>;
> > +			vfront-porch = <4>;
> > +			vback-porch = <36>;
> > +			vsync-len = <5>;
> > +			de-active = <1>;
> > +		};
> > +
> > +		ports {
> > +			#address-cells = <1>;
> > +			#size-cells = <0>;
> > +
> > +			port@0 {
> > +				reg = <0>;
> > +
> > +				dual-lvds-odd-pixels;
> 
> Add one empty line between properties and subnodes. Drop empty line
> between reg and dual-foo-pixels.
> 
> > +				panel_in_lvds_odd: endpoint {
> > +					remote-endpoint = <&lt9211c_out_odd>;
> > +				};
> > +			};
> > +
> > +			port@1 {
> > +				reg = <1>;
> > +
> > +				dual-lvds-even-pixels;
> > +				panel_in_lvds_even: endpoint {
> > +					remote-endpoint = <&lt9211c_out_even>;
> > +				};
> > +
> > +			};
> > +		};
> > +	};
> > +
> > +};
> > +
> > +&i2c1 {
> > +	status = "okay";
> 
> No clock-frequency?
> 
> > +
> > +	lvds_bridge: lvds-bridge@29 {
> > +		compatible = "lontium,lt9211c";
> 
> Not supported in mainline and not described as a dependency in the cover
> letter.
> 
> > +		reg = <0x29>;
> > +		reset-gpios = <&tlmm 117 1>;
> 
> Use GPIO_ACTIVE_foo
> 
> > +
> > +		status = "okay";
> > +
> > +		ports {
> > +			#address-cells = <1>;
> > +			#size-cells = <0>;
> > +
> > +			port@0 {
> > +				reg = <0>;
> > +
> > +				lt9211c_in: endpoint {
> > +					data-lanes = <0 1 2 3>;
> > +					remote-endpoint = <&mdss_dsi0_out>;
> > +				};
> > +			};
> > +
> > +			port@2 {
> > +				reg = <2>;
> > +
> > +				lt9211c_out_odd: endpoint {
> > +					remote-endpoint = <&panel_in_lvds_odd>;
> > +				};
> > +			};
> > +
> > +			port@3 {
> > +				reg = <3>;
> > +
> > +				lt9211c_out_even: endpoint {
> > +					remote-endpoint = <&panel_in_lvds_even>;
> > +				};
> > +			};
> > +		};
> > +	};
> > +
> > +
> > +};
> > +
> > +&lt9611_codec {
> > +	status = "disabled";
> > +};
> > +
> > +&mdss_dsi0_out {
> > +	remote-endpoint = <&lt9211c_in>;
> > +};
> > +
> >  &spi11 {
> >  	#address-cells = <1>;
> >  	#size-cells = <0>;
> > 
> > -- 
> > 2.34.1
> > 
> 
> -- 
> With best wishes
> Dmitry