sunxi-mmc: A733 IDMAC stuck in descriptor rea

[Enzo]

Hi,

On A733/SUN60IW2, SDMMC0 works with PIO reads but normal IDMAC does not
fetch the first descriptor.

This is on a Radxa Cubie A7S, testing Linux v7.1-rc6-gabc8d07b0a63.

The failing transfer is a single 8-block CMD18.  After starting IDMAC:

    IDST = 0x00004000
    CHDA = DLBA
    CBDA = 0
    CBCR = 0x400
    BBCR = 0
    descriptor OWN is still set

The descriptor memory is unchanged after syncing for CPU, so this looks
like the controller never reads descriptor word 0.

I have already checked the obvious descriptor/DMA cases: 4K descriptor
size, shifted descriptor/data addresses, descriptor memory below 4G,
coherent vs streaming descriptors, and the normal-IDMAC 64-bit DMA mask
used by the vendor tree.

Is there an A733-specific clock/reset, MBUS/NSI, firewall, or firmware
handoff bit needed before SDMMC0 IDMAC can access memory?

I can send the full boot log and instrumented dmesg if useful.

Thanks for your time,

Enzo Adriano
enzo.adriano.code at gmail.com