linux-kernel - Re: [PATCH] ARM: dts: bcm2711-rpi: Use aliases to set custom MMC device index

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Date:   Wed, 29 Jun 2022 15:44:26 -0300
From:   Ariel D'Alessandro <ariel.dalessandro@...labora.com>
To:     Stefan Wahren <stefan.wahren@...e.com>,
        krzysztof.kozlowski+dt@...aro.org, nsaenz@...nel.org,
        robh+dt@...nel.org
Cc:     bcm-kernel-feedback-list@...adcom.com, devicetree@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        pbrobinson@...il.com, f.fainelli@...il.com
Subject: Re: [PATCH] ARM: dts: bcm2711-rpi: Use aliases to set custom MMC
 device index

Hi Stefan,

Sorry for the delay.

On 6/14/22 17:47, Stefan Wahren wrote:
> Hi Ariel,
> 
> Am 14.06.22 um 16:12 schrieb Ariel D'Alessandro:
>> Add MMC aliases to ensure that the /dev/mmcblk ID for the first
>> eMMC/SD card won't change depending on the probe order of the MMC
>> drivers.
> 
> this changes the emmc2 from mmc1 to mmc0 in my case (RPi 4,
> multi_v7_defconfig), which i consider as a regression / unexpected
> change in userspace.
> 
> Could you please explain your actual motivation of your patch?

That's a good point. The original reason comes from u-boot in fact, I
just sent the patch here as u-boot is syncing the dts files from the kernel.

U-boot uses the same defconfig `configs/rpi_arm64_defconfig` for
different RPi versions, which have different mmcblk ids numbering.

In order to use bootcount support in u-boot, the config option
CONFIG_SYS_BOOTCOUNT_EXT_DEVPART needs to be filled with the fixed
dev/part ids. In general I'd expect mmcblk0 to be eMMC/SD, which is not
in this case, at least for RPi4.

Anyway, this is probably something to be discussed on the u-boot mailing
list, not here.

Thanks,
Ariel

> 
>>
>> Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@...labora.com>
>> ---
>>
>> Changes in v2:
>> * Moved alias from bcm2711-rpi-4-b.dts to bcm2711-rpi.dtsi
>>
>>   arch/arm/boot/dts/bcm2711-rpi.dtsi | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm/boot/dts/bcm2711-rpi.dtsi
>> b/arch/arm/boot/dts/bcm2711-rpi.dtsi
>> index ca266c5d9f9b..a39b2f68e4cc 100644
>> --- a/arch/arm/boot/dts/bcm2711-rpi.dtsi
>> +++ b/arch/arm/boot/dts/bcm2711-rpi.dtsi
>> @@ -13,6 +13,7 @@ memory@0 {
>>       aliases {
>>           emmc2bus = &emmc2bus;
>>           ethernet0 = &genet;
>> +        mmc0 = &emmc2;    /* mmcblk0 for eMMC/SD */
>>           pcie0 = &pcie0;
>>           blconfig = &blconfig;
>>       };