Enable ddr modes on emmc2 of Raspberry Pi 4 B

[Stefan Wahren]

Hi Tobias,

thanks for providing this patch to lkml [1]. I sent a very similiar one
[2] to linux-mmc after the investigations on the Raspberry Pi github [3].

Can you please explain why this sd-uhs-ddr50 property is necessary?

From my testings with a UHS SD card the UHS DDR50 mode is already
properly configured before your patch.

Is there a specific combination which doesn't work?

Please provide the ios settings of /sys/kernel/debug/mmc1/ios in this
case before applying your patch.

Best regards

[1] -
https://lore.kernel.org/lkml/20200829231509.543901-2-t.schramm@manjaro.org/

[2] - https://marc.info/?l=linux-mmc&m=159865133820037

[3] - https://github.com/raspberrypi/linux/issues/3802