linux-kernel - Re: [PATCH 3/3] arch: arm64: ti: Add support for AM68 SK base board

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Date:   Thu, 3 Nov 2022 08:42:03 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sinthu Raja M <sinthu.raja@...tralsolutions.com>
Cc:     Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Sinthu Raja <sinthu.raja@...com>
Subject: Re: [PATCH 3/3] arch: arm64: ti: Add support for AM68 SK base board

On 03/11/2022 04:38, Sinthu Raja M wrote:
> On Tue, Oct 18, 2022 at 6:33 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> On 18/10/2022 08:38, Sinthu Raja wrote:
>>> From: Sinthu Raja <sinthu.raja@...com>
>>>
>>> The SK architecture comprises of baseboard and a SOM board. It is
>>> as follows,
>>>
>>>        +--------------------------------------+---+
>>>        |                                      |   |<--Connectors
>>>        |                                      +---|
>>>        |      +---------------------------+   |   |
>>>        |      | SOM                       |   +---|
>>>        |      |                           |   |   |
>>>        |      |                           |   +---| Power Supply
>>>        |      |                           |       |   |
>>>        |      +---------------------------+       |   |
>>>        |                                          |<--+
>>>        |           BASE BOARD                     |
>>>        +------------------------------------------+
>>
>> This is pretty straightforward for SoM, I am not sure what's the benefit
>> to add it.
>>
>>>
>>> AM68 Starter Kit's baseboard contains most of the actual connectors,
>>> power supply etc. The System on Module (SoM) is plugged on to the base
>>> board. Therefore, add support for peripherals brought out in the base
>>> board.
>>>
>>> Schematics: https://www.ti.com/lit/zip/SPRR463
>>>
>>> Signed-off-by: Sinthu Raja <sinthu.raja@...com>
>>> ---
>>>  arch/arm64/boot/dts/ti/Makefile               |   2 +
>>>  .../boot/dts/ti/k3-am68-sk-base-board.dts     | 459 ++++++++++++++++++
>>>  2 files changed, 461 insertions(+)
>>>  create mode 100644 arch/arm64/boot/dts/ti/k3-am68-sk-base-board.dts
>>>
>>> diff --git a/arch/arm64/boot/dts/ti/Makefile b/arch/arm64/boot/dts/ti/Makefile
>>> index 4555a5be2257..498b089d96f8 100644
>>> --- a/arch/arm64/boot/dts/ti/Makefile
>>> +++ b/arch/arm64/boot/dts/ti/Makefile
>>> @@ -19,6 +19,8 @@ dtb-$(CONFIG_ARCH_K3) += k3-j7200-common-proc-board.dtb
>>>
>>>  dtb-$(CONFIG_ARCH_K3) += k3-j721s2-common-proc-board.dtb
>>>
>>> +dtb-$(CONFIG_ARCH_K3) += k3-am68-sk-base-board.dtb
>>> +
>>
>> Alphabetical order, although does not look like other entries are ordered...
>>
>>>  dtb-$(CONFIG_ARCH_K3) += k3-am642-evm.dtb
>>>  dtb-$(CONFIG_ARCH_K3) += k3-am642-sk.dtb
>>>
>>> diff --git a/arch/arm64/boot/dts/ti/k3-am68-sk-base-board.dts b/arch/arm64/boot/dts/ti/k3-am68-sk-base-board.dts
>>> new file mode 100644
>>> index 000000000000..f51cbd2e3b72
>>> --- /dev/null
>>> +++ b/arch/arm64/boot/dts/ti/k3-am68-sk-base-board.dts
>>> @@ -0,0 +1,459 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * Copyright (C) 2022 Texas Instruments Incorporated - https://www.ti.com/
>>> + *
>>> + * Base Board: https://www.ti.com/lit/zip/SPRR463
>>> + */
>>> +
>>> +/dts-v1/;
>>> +
>>> +#include "k3-am68-sk-som.dtsi"
>>> +#include <dt-bindings/net/ti-dp83867.h>
>>> +#include <dt-bindings/phy/phy-cadence.h>
>>> +#include <dt-bindings/phy/phy.h>
>>> +#include <dt-bindings/mux/ti-serdes.h>
>>> +
>>> +/ {
>>> +     compatible = "ti,am68-sk", "ti,j721s2";
>>> +     model = "Texas Instruments AM68 SK";
>>> +
>>> +     chosen {
>>> +             stdout-path = "serial2:115200n8";
>>> +             bootargs = "console=ttyS2,115200n8 earlycon=ns16550a,mmio32,0x2880000";
>>
>> None of these bootargs are suitable for mainline. earlycon for sure - it
>> is pure debug option.
> Krzysztof,
> In AM68 SK the Linux console is on main_uart8, so to be consistent
> with other J7 families of devices aliasing the serial port to ttyS2. I
> am quite confused why these bootargs are not suitable for mainline. I
> check the below documentation section 2.3, as mentioned it can be used
> as kernel parameters. Please correct me if I am wrong.
> https://www.kernel.org/doc/html/latest/devicetree/usage-model.html?highlight=bootargs

Why? Console is defined by stdout path, so why do you need to redefine
it? Bootargs are for debugging so why all users in entire world by
default must debug?

Best regards,
Krzysztof