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Message-ID: <5f117868-71f9-4412-a6c6-bbe7914390f6@gmail.com>
Date: Fri, 14 Nov 2025 15:25:10 +0530
From: Tessolve Upstream <tessolveupstream@...il.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: konradybcio@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
conor+dt@...nel.org, linux-arm-msm@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] arm64: dts: qcom: talos-evk: Add support for
dual-channel LVDS panel
On 06/11/25 04:13, Bjorn Andersson wrote:
> On Fri, Oct 31, 2025 at 02:42:05PM +0530, Tessolve Upstream wrote:
>>
>>
>> On 29/10/25 21:18, Bjorn Andersson wrote:
>>> On Tue, Oct 28, 2025 at 11:46:36AM +0530, Sudarshan Shetty wrote:
>>>> This patch introduces a new device tree for the QCS615 Talos
>>>
>>> "This patch" doesn't make sense when you look at the git log once the
>>> patch has been accepted, please avoid it.
>>>
>>> Please read https://docs.kernel.org/process/submitting-patches.html#describe-your-changes
>>>
>>> Start your commit message with a "problem description", describe what
>>> this LVDS talos is, why it should have it's own dts file etc.
>>
>> Okay, will update in next patch.
>>>
>>>> EVK platform with dual-channel LVDS display support.
>>>>
>>>> The new DTS file (`talos-evk-lvds.dts`) is based on the existing
>>>> `talos-evk.dts` and extends it to enable a dual-channel LVDS display
>>>> configuration using the TI SN65DSI84 DSI-to-LVDS bridge.
>>>>
>>>> where channel-A carries odd pixel and channel-B carries even pixel
>>>> on the QCS615 talos evk platform.
>>>>
>>>> Signed-off-by: Sudarshan Shetty <tessolveupstream@...il.com>
>>>> ---
>>>> arch/arm64/boot/dts/qcom/Makefile | 1 +
>>>> arch/arm64/boot/dts/qcom/talos-evk-lvds.dts | 128 ++++++++++++++++++++
>>>> 2 files changed, 129 insertions(+)
>>>> create mode 100644 arch/arm64/boot/dts/qcom/talos-evk-lvds.dts
>>>>
>>>> diff --git a/arch/arm64/boot/dts/qcom/Makefile b/arch/arm64/boot/dts/qcom/Makefile
>>>> index d5a3dd98137d..6e7b04e67287 100644
>>>> --- a/arch/arm64/boot/dts/qcom/Makefile
>>>> +++ b/arch/arm64/boot/dts/qcom/Makefile
>>>> @@ -307,6 +307,7 @@ dtb-$(CONFIG_ARCH_QCOM) += sm8750-mtp.dtb
>>>> dtb-$(CONFIG_ARCH_QCOM) += sm8750-qrd.dtb
>>>> dtb-$(CONFIG_ARCH_QCOM) += talos-evk.dtb
>>>> dtb-$(CONFIG_ARCH_QCOM) += talos-evk-dsi.dtb
>>>> +dtb-$(CONFIG_ARCH_QCOM) += talos-evk-lvds.dtb
>>>> x1e001de-devkit-el2-dtbs := x1e001de-devkit.dtb x1-el2.dtbo
>>>> dtb-$(CONFIG_ARCH_QCOM) += x1e001de-devkit.dtb x1e001de-devkit-el2.dtb
>>>> x1e78100-lenovo-thinkpad-t14s-el2-dtbs := x1e78100-lenovo-thinkpad-t14s.dtb x1-el2.dtbo
>>>> diff --git a/arch/arm64/boot/dts/qcom/talos-evk-lvds.dts b/arch/arm64/boot/dts/qcom/talos-evk-lvds.dts
>>>> new file mode 100644
>>>> index 000000000000..7ba4ab96ada6
>>>> --- /dev/null
>>>> +++ b/arch/arm64/boot/dts/qcom/talos-evk-lvds.dts
>>>> @@ -0,0 +1,128 @@
>>>> +// SPDX-License-Identifier: BSD-3-Clause
>>>> +/*
>>>> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
>>>> + */
>>>> +/dts-v1/;
>>>> +#include "talos-evk.dts"
>>>
>>> We don't include .dts files, split the existing one in a dtsi and dts
>>> file and then include the dtsi here. Or provide provide this as a dtso
>>> overlay on top of the dts.
>>>
>>> It's not clear to me which is the correct way, because you didn't
>>> adequately described how the SN65DSI84 enter the picture. Is it always
>>> there, but not part of the standard dip-switch configuration? Or is this
>>> some mezzanine?
>>>
>>> Regards,
>>> Bjorn
>>>
>>
>> Thanks for the feedback.
>> Currently, the Talos device tree hierarchy is organized as follows:
>>
>> talos-som.dtsi — defines SoM-specific interfaces
>> talos-evk.dts — adds carrier board (CB) interfaces such as MicroSD, power
>> button, and HDMI
>> talos-evk-lvds.dts — enables the LVDS display (includes SoM + CB +
>> LVDS + disables HDMI)
>>
>> The LVDS and HDMI displays share a common DSI output, so only one
>> interface can be active at a time. At present, talos-evk-lvds.dts
>> includes talos-evk.dts directly so that the base SoM and carrier
>> interfaces (e.g., MicroSD, power button) remain available.
>>
>
> Are you saying that there are 2 PCBs involved:
Yes, 2 PCBs involved,
> 1) The SOM
> 2) The EVK
>
> And then perhaps a DIP switch or something to disable HDMI and select
> LVDS?
DIP switch is used to select either HDMI or LVDS
>
> Or are you saying there are 3 PCBs:
No.
> 1) The SOM
> 2) The EVK
> 3) Something that provides LVDS - and disables HDMI on the EVK
>
>> However, as you pointed out, including a .dts file directly is not
>> recommended upstream. To address this, I am considering the following
>> restructuring options:
>>
>> Option 1: Introduce a talos-cb.dtsi
>>
>> talos-som.dtsi: SoM-specific interfaces
>> talos-cb.dtsi: common carrier board interfaces (MicroSD, power button, etc.)
>
> I'm guessing that what you call "carrier board" most would call "EVK"?
Yes.
>
>> talos-evk.dts: includes talos-som.dtsi + talos-cb.dtsi + HDMI
>> talos-evk-lvds.dts: includes talos-som.dtsi + talos-cb.dtsi + LVDS
>
>
>>
>> This approach avoids including .dts files directly and keeps the carrier
>> board interfaces centralized and reusable.It also cleanly separates SoM
>> and CB content and is consistent with how other Qualcomm platforms
>> structure their EVK variants.
>
> Can you point to an example where this is done?
>
> The examples that comes to mind is e.g. the vison board/mezzanine. Those
> are separate physical things that you plug on top of the other boards,
> that's why they are described the way they are.
This example that comes to mind. Which is restructuring code that matches
Device Tree and hardware.
>
>>
>> Option 2: Move CB interfaces to talos-som.dtsi (disabled by default)
>>
>> Move MicroSD, power button, etc., to talos-som.dtsi with status = "disabled";
>
> If those components are physically mounted on the SOM, then that is the
> correct thing to do.
>
> If you suggest moving them there to solve some other problem, then it's
> not the right solution.
Understood.
>
>> Enable these interfaces in each top-level DTS (e.g., talos-evk.dts,
>> talos-evk-lvds.dts)
>> While this also avoids .dts inclusion, it may make the SoM DTS
>> unnecessarily complex and less reusable, as those CB-specific
>> peripherals don’t belong to the SoM hardware.
>>
>> Let me know your prepared approach here.
>
> My preferred approach is that you write DeviceTree that matches the
> hardware in front of you.
Which is taken care in v2 patch.
https://lore.kernel.org/all/20251104125208.1009695-1-tessolveupstream@gmail.com/T/#u
>
> Regards,
> Bjorn
>
>>>> +
>>>> +/ {
>>>> +
>>>> + backlight: backlight {
>>>> + compatible = "gpio-backlight";
>>>> + gpios = <&tlmm 115 GPIO_ACTIVE_HIGH>;
>>>> + default-on;
>>>> + };
>>>> +
>>>> + lcd0_pwm_en {
>>>> + compatible = "pwm-gpio";
>>>> + gpios = <&tlmm 59 GPIO_ACTIVE_HIGH>;
>>>> + pinctrl-0 = <&lcd0_bklt_pwm>;
>>>> + pinctrl-names = "default";
>>>> + #pwm-cells = <3>;
>>>> + };
>>>> +
>>>> + panel-lvds {
>>>> + compatible = "auo,g133han01";
>>>> +
>>>> + ports {
>>>> + #address-cells = <1>;
>>>> + #size-cells = <0>;
>>>> +
>>>> + /* LVDS A (Odd pixels) */
>>>> + port@0 {
>>>> + reg = <0>;
>>>> + dual-lvds-odd-pixels;
>>>> +
>>>> + lvds_panel_out_a: endpoint {
>>>> + remote-endpoint = <&sn65dsi84_out_a>;
>>>> + };
>>>> + };
>>>> +
>>>> + /* LVDS B (Even pixels) */
>>>> + port@1 {
>>>> + reg = <1>;
>>>> + dual-lvds-even-pixels;
>>>> +
>>>> + lvds_panel_out_b: endpoint {
>>>> + remote-endpoint = <&sn65dsi84_out_b>;
>>>> + };
>>>> + };
>>>> + };
>>>> + };
>>>> +};
>>>> +
>>>> +&adv7535 {
>>>> + status = "disabled";
>>>> +};
>>>> +
>>>> +&i2c1 {
>>>> + clock-frequency = <400000>;
>>>> +
>>>> + status = "okay";
>>>> +
>>>> + sn65dsi84: sn65dsi84@2c {
>>>> + compatible = "ti,sn65dsi84";
>>>> + reg = <0x2c>;
>>>> + enable-gpios = <&tlmm 42 GPIO_ACTIVE_HIGH>;
>>>> + ti,dsi-lanes = <4>;
>>>> + ti,lvds-format = "jeida-24";
>>>> + ti,lvds-bpp = <24>;
>>>> +
>>>> + ports {
>>>> + #address-cells = <1>;
>>>> + #size-cells = <0>;
>>>> +
>>>> + port@0 {
>>>> + reg = <0>;
>>>> +
>>>> + sn65dsi84_in: endpoint {
>>>> + data-lanes = <0 1 2 3>;
>>>> + remote-endpoint = <&mdss_dsi0_out>;
>>>> + };
>>>> + };
>>>> +
>>>> + port@2 {
>>>> + reg = <2>;
>>>> +
>>>> + sn65dsi84_out_a: endpoint {
>>>> + data-lanes = <0 1 2 3>;
>>>> + remote-endpoint = <&lvds_panel_out_a>;
>>>> + };
>>>> + };
>>>> +
>>>> + port@3 {
>>>> + reg = <3>;
>>>> +
>>>> + sn65dsi84_out_b: endpoint {
>>>> + data-lanes = <0 1 2 3>;
>>>> + remote-endpoint = <&lvds_panel_out_b>;
>>>> + };
>>>> + };
>>>> + };
>>>> + };
>>>> +};
>>>> +
>>>> +&mdss_dsi0 {
>>>> + vdda-supply = <&vreg_l11a>;
>>>> +
>>>> + status = "okay";
>>>> +};
>>>> +
>>>> +&mdss_dsi0_out {
>>>> + remote-endpoint = <&sn65dsi84_in>;
>>>> + data-lanes = <0 1 2 3>;
>>>> +};
>>>> +
>>>> +&tlmm {
>>>> + lcd0_bklt_en: lcd0-bklt-en-state {
>>>> + pins = "gpio115";
>>>> + function = "gpio";
>>>> + bias-disable;
>>>> + };
>>>> +
>>>> + lcd0_bklt_pwm: lcd0-bklt-pwm-state {
>>>> + pins = "gpio59";
>>>> + function = "gpio";
>>>> + bias-disable;
>>>> + };
>>>> +};
>>>> --
>>>> 2.34.1
>>>>
>>
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