AML-S905X-CC-V2 emmc issue

[Jeff Sacksteder]

I'm having a problem trying to install Alpine Linux on to a Libre
Computing Sweet Potato AML-S905X-CC-V2 and I need some clairification,
if someone has been down this road already.

The sd card is detected, but the optional emmc module is not(per dmesg
and /dev/mmc*).

The suggested distros Libre suggests work correctly, so I know the
hardware is good.

I don't know if they have magic patches, so looking for clues
elsewhere, the current Gentoo image for Arm correctly detects both
devices.

The first obvious difference I find vs Alpine is that they include
PWRSEQ_EMMC compiled as a module, while Alpine does not configure that
option at all. My operating theory is that this hardware needs some
bring-up power negotiation before it is available.

However, since I don't have a cross-compile environment available, and
it takes 35 hrs to build a kernel, and the Alpine build process is
convoluted and weird to me, I would really like to know if that single
option is the solution. Otherwise I face multiple 35 hr cycles of
building and testing.