linux-kernel - Re: [PATCH] ARM: dts: exynos: Assign a fixed index to mmc devices on exynos4412 based ODROID boards

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Date:   Wed, 4 Nov 2020 14:44:10 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Markus Reichl <m.reichl@...etechno.de>,
        Rob Herring <robh+dt@...nel.org>,
        Kukjin Kim <kgene@...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 exynos4412 based ODROID boards

On 04.11.2020 14:13, Marek Szyprowski wrote:
> On 04.11.2020 14:06, Markus Reichl wrote:
>> Am 04.11.20 um 13:25 schrieb Marek Szyprowski:
>>> On 04.11.2020 11:25, 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
>>>> ar not practical.
>>>> Use newly introduced aliases for mmcblk devices from [1].
>>>>
>>>> [1]
>>>> https://patchwork.kernel.org/patch/11747669/
>>>>
>>>> Signed-off-by: Markus Reichl <m.reichl@...etechno.de>
>>>> ---
>>>>    arch/arm/boot/dts/exynos4412-odroid-common.dtsi | 5 +++++
>>>>    1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/arch/arm/boot/dts/exynos4412-odroid-common.dtsi
>>>> b/arch/arm/boot/dts/exynos4412-odroid-common.dtsi
>>>> index a5c1ce1e396c..aa10d5bc7e1c 100644
>>>> --- a/arch/arm/boot/dts/exynos4412-odroid-common.dtsi
>>>> +++ b/arch/arm/boot/dts/exynos4412-odroid-common.dtsi
>>>> @@ -13,6 +13,11 @@
>>>>    #include "exynos-mfc-reserved-memory.dtsi"
>>>>      / {
>>>> +    aliases {
>>>> +        mmc0 = &sdhci_2;
>>>> +        mmc1 = &mshc_0;
>>> Like in the OdroidXU3-family patch, I would use 0 for the eMMC (mshc_0)
>>> and 2 for the SD-card (sdhci_2).
>> How to deal then with sdhci_0 (from exynos4.dtsi) vc. mshc_0 (from
>> exynos4412.dts)?
> sdhci_0 and mshc_0 both operate on the same physical MMC0 bus, so this
> is not an issue. They cannot be used simultaneously. The latter is just
> faster, the first one has been left there mainly for the software
> compatibility.

I've thought a bit more on this and I would simply prefer to add generic 
MMC aliases to the top-level Exynos dtsi files (3250, 4210, 4412, 5250, 
5410, 5420) to keep Linux logical MMC bus numbers in sync with the HW 
bus numbers on all boards.

Best regards

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