linux-kernel - Re: [PATCH] ARM: dts: exynos: Add a placeholder for a MAC address

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Message-ID: <dleftjr1qigx6p.fsf%l.stelmach@samsung.com>
Date:   Thu, 01 Oct 2020 10:36:14 +0200
From:   Lukasz Stelmach <l.stelmach@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, Kukjin Kim <kgene@...nel.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        b.zolnierkie@...sung.com, m.szyprowski@...sung.com
Subject: Re: [PATCH] ARM: dts: exynos: Add a placeholder for a MAC address

It was <2020-10-01 czw 09:22>, when Krzysztof Kozlowski wrote:
> On Wed, Sep 30, 2020 at 04:31:51PM +0200, Łukasz Stelmach wrote:
>> Add a placeholder for a MAC address. A bootloader may fill it
>> to set the MAC address and override EEPROM settings.
>> 
>> Signed-off-by: Łukasz Stelmach <l.stelmach@...sung.com>
>> ---
>>  arch/arm/boot/dts/exynos5422-odroidxu3.dts | 18 ++++++++++++++++++
>>  1 file changed, 18 insertions(+)
>> 
>> diff --git a/arch/arm/boot/dts/exynos5422-odroidxu3.dts b/arch/arm/boot/dts/exynos5422-odroidxu3.dts
>> index db0bc17a667b..9f7f3eacb750 100644
>> --- a/arch/arm/boot/dts/exynos5422-odroidxu3.dts
>> +++ b/arch/arm/boot/dts/exynos5422-odroidxu3.dts
>> @@ -70,3 +70,21 @@ &pwm {
>>  &usbdrd_dwc3_1 {
>>  	dr_mode = "peripheral";
>>  };
>> +
>> +&usbhost2 {
>> +	#address-cells = <1>;
>> +	#size-cells = <0>;
>> +
>> +	hub@1 {
>> +		compatible = "usb8087,0024";
>> +		reg = <1>;
>> +		#address-cells = <1>;
>> +		#size-cells = <0>;
>> +
>> +		ethernet: usbether@1 {
>> +			compatible = "usb0c45,6310";
>> +			reg = <1>;
>> +			mac-address = [00 00 00 00 00 00]; /* Filled in by a bootloader */
>
> Why do you need a placeholder? U-Boot can just append the
> address/property.

Several other dts files have such placeholder

git grep 'mac-addr.*\[00 00 00 00 00 00\]' arch/arm/boot/dts/ | wc -l
26

I can see two scenarios where this patch may be helpful. Another
(simple) boot loading code might be used. The value may also be
customized during build time and used without any support of a
bootloader.

Finding and filling a placeholder would be easier in u-boot too.

And it serves as a reference how to configure a USB device in a dts
file.

-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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