linux-kernel - Re: [PATCH] ARM: dts: exynos: Assign a fixed index to mmc devices on ODROID XU3/4 boards

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Message-ID: <f78943ff-fb41-b2b8-5c50-0f46386a720c@samsung.com>
Date:   Wed, 4 Nov 2020 13:56:12 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Markus Reichl <m.reichl@...etechno.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: exynos: Assign a fixed index to mmc devices
 on ODROID XU3/4 boards

Hi Markus,

On 04.11.2020 13:42, Markus Reichl wrote:
> Am 04.11.20 um 13:24 schrieb Marek Szyprowski:
>> On 04.11.2020 11:08, Markus Reichl wrote:
>>> Recently introduced async probe on mmc devices can shuffle block IDs.
>>> Pin them to fixed values to ease booting in evironments where UUIDs
>>> are not practical. Use newly introduced aliases for mmcblk devices 
>>> from [1].
>>>
>>> [1]
>>> https://patchwork.kernel.org/patch/11747669/
>>
>> Wow, this is a long standing issue, called by others 'a feature'. Good
>> that this has been finally solved.
>>
>>> Signed-off-by: Markus Reichl <m.reichl@...etechno.de>
>>> ---
>>>   arch/arm/boot/dts/exynos5422-odroidxu3-common.dtsi | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>>> diff --git a/arch/arm/boot/dts/exynos5422-odroidxu3-common.dtsi 
>>> b/arch/arm/boot/dts/exynos5422-odroidxu3-common.dtsi
>>> index e35af40a55cb..91d2840ac8ca 100644
>>> --- a/arch/arm/boot/dts/exynos5422-odroidxu3-common.dtsi
>>> +++ b/arch/arm/boot/dts/exynos5422-odroidxu3-common.dtsi
>>> @@ -13,6 +13,11 @@
>>>   #include "exynos5422-odroid-core.dtsi"
>>>     / {
>>> +    aliases {
>>> +        mmc0 = &mmc_2;
>>> +        mmc1 = &mmc_0;
>>
>> Frankly, I would keep the MMC numbers the same as in u-boot and
>> datasheets. 0 for the build-in eMMC and 2 for the SD-card. This would be
>> much more natural. On the other hand, I would agree to do it differently
>> only on Odroid HC1/HD2/MC1, which don't have build-in eMMC - just use 0
>> there for the SD-card.
>
> This would break present and long standing  boot ordering in mainline, 
> which is
> mmcblk0 = SD-card and
> mmcblk1 = eMMC
>
> Still desired?

Well, previously (before v4.0? I don't remember exactly when there was a 
first change), the order was exactly opposite. I think that going for 
the MMC bus numbers from the datasheet/schematic is the most appropriate 
approach.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland