linux-kernel - Re: [PATCH 1/3] arm64: dts: ti: iot2050: Flip mmc device ordering on Advanced devices

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Message-ID: <20210907165316.4s3jrouctcpc3kvo@pessimism>
Date:   Tue, 7 Sep 2021 11:53:16 -0500
From:   Nishanth Menon <nm@...com>
To:     Aswath Govindraju <a-govindraju@...com>
CC:     Jan Kiszka <jan.kiszka@...mens.com>,
        Tero Kristo <kristo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        Bao Cheng Su <baocheng.su@...mens.com>,
        Chao Zeng <chao.zeng@...mens.com>
Subject: Re: [PATCH 1/3] arm64: dts: ti: iot2050: Flip mmc device ordering on
 Advanced devices

On 22:17-20210907, Aswath Govindraju wrote:
> Hi Nishanth,
> 
> On 07/09/21 9:05 pm, Nishanth Menon wrote:
> > On 17:30-20210907, Jan Kiszka wrote:
> >> On 07.09.21 17:27, Nishanth Menon wrote:
> >>> On 17:20-20210907, Jan Kiszka wrote:
> >>>> On 07.09.21 17:13, Nishanth Menon wrote:
> >>>>> On 16:22-20210907, Jan Kiszka wrote:
> >>>>>> From: Jan Kiszka <jan.kiszka@...mens.com>
> >>>>>>
> >>>>>> This ensures that the SD card will remain mmc0 across Basic and Advanced
> >>>>>> devices, also avoiding surprises for users coming from the downstream
> >>>>>> kernels.
> >>>>>>
> >>>>>> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
> >>>>>> ---
> >>>>>>  arch/arm64/boot/dts/ti/k3-am6548-iot2050-advanced.dts | 5 +++++
> >>>>>>  1 file changed, 5 insertions(+)
> >>>>>>
> >>>>>> diff --git a/arch/arm64/boot/dts/ti/k3-am6548-iot2050-advanced.dts b/arch/arm64/boot/dts/ti/k3-am6548-iot2050-advanced.dts
> >>>>>> index ec9617c13cdb..d1d5278e0b94 100644
> >>>>>> --- a/arch/arm64/boot/dts/ti/k3-am6548-iot2050-advanced.dts
> >>>>>> +++ b/arch/arm64/boot/dts/ti/k3-am6548-iot2050-advanced.dts
> >>>>>> @@ -18,6 +18,11 @@ / {
> >>>>>>  	compatible = "siemens,iot2050-advanced", "ti,am654";
> >>>>>>  	model = "SIMATIC IOT2050 Advanced";
> >>>>>>  
> >>>>>> +	aliases {
> >>>>>> +		mmc0 = &sdhci1;
> >>>>>> +		mmc1 = &sdhci0;
> >>>>>> +	};
> >>>>>
> >>>>>
> >>>>> Should we do this at SoC level?
> >>>>>
> >>>>
> >>>> Well, I wouldn't mind - but that would also impact your EVMs. For us,
> >>>> this is fine as we are coming from that ordering above with our
> >>>> downstream kernel/dts.
> >>>>
> >>>
> >>> I think it'd probably be a welcome change. overall we've standardized on
> >>> partuuid.
> >>>
> >>
> >> Yeah, it's more about "dd if=emmc.img of=/dev/mmcblk1 - damn, the wrong
> >> one again."
> >>
> >> Let me know what you prefer, and I'll update my patch.
> > 
> > 
> > Lets do it at SoC level. I will follow it up with a patch for other K3
> > SoCs as well.
> > 
> > 
> > Unless someone has a strong opinion on this approach - if so, speak up
> > with reasons.
> > 
> 
> Making this change in SoC level for all K3 devices would force changes
> to be made in U-Boot too, for consistency. In U-Boot, a major change
> would be required in the environment variables to support this. As I
> don't see any functional advantage by making this change, I feel that
> this change would make things more confusing for users already using the
> K3 devices. At present, the ordering is consistent across all the K3
> devices, I feel that keeping it the same way would be better.
> 
> As for making changes only on IoT boards, if it is okay to have the
> ordering changed between U-Boot and kernel, I don't see any problem
> making this change in kernel alone.


arch/arm64/boot/dts/ti/k3-am65.dtsi has no ordering. u-boot is supposed
to copy from kernel the dtsi files as is. I think having mmc aliases in
kernel is a good thing as we do regard kernel as the canonical dts
source.

If you are suggesting we flip things so that mmc0 is sdhci0 and mmc1 is
sdhci1 -  that might be a valid suggestion - Jan, do you see a problem
in having consistency here (flip the aliases)?


-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D