Message-ID: <52c27c60-65c2-4a36-b1c6-3edb7e97969f@gmail.com>
Date: Tue, 4 Nov 2025 12:19:43 +0530
From: Tessolve Upstream <tessolveupstream@...il.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>, 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 01/11/25 14:13, Dmitry Baryshkov 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?
>>
>> Thanks for the feedback.
> 
> You didn't answer the question. It was about the hardware, not about
> DTs.
> 
>> 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)
> 
> So, is LVDS a part of the standard board or is it a mezzanine?

Yes, The LVDS SN65DSI84 bridge and panel connector, is part of the standard
board. 
> 
>>
>> 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.
>>
>> 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.)
>> 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.
> 
> This sounds okay, but please respond to previous questions.
I hope I addressed previous question.
I will go with this option, and update v2 patch accordingly.
> 
>>
>> Option 2: Move CB interfaces to talos-som.dtsi (disabled by default)
> 
> Why? What happens when somebody reuses the SoM with some other base
> board?
> 
>>
>> Move MicroSD, power button, etc., to talos-som.dtsi with status = "disabled";
>> 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.
> 
> If you yourself don't like the second option, why do you propose it?
> 

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