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 14:13:41 +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

Hi Markus,

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.

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