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

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Message-ID: <20201105082212.GA23722@kozik-lap>
Date:   Thu, 5 Nov 2020 09:22:12 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Markus Reichl <m.reichl@...etechno.de>,
        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
Subject: Re: [PATCH] ARM: dts: exynos: Assign a fixed index to mmc devices on
 exynos4412 based ODROID boards

On Wed, Nov 04, 2020 at 02:44:10PM +0100, Marek Szyprowski wrote:
> 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.

I like this approach - I don't see much benefit of having different
numbering between boards of the same SoC.

Let's match old U-Boot behavior (I assume that people switch to PARTUUID
around the v4.0 mixup, so they should not be affected).

Best regards,
Krzysztof