DT property keep-power-in-suspend and how WiFi drivers use it

Hello,

I have a question regarding the usage of the Device Tree property 
`keep-power-suspend`.

In the Device Tree documentation it reads:
"SDIO only. Preserves card power during a suspend/resume cycle."

Does that mean that the SDIO Host Controller will remain powered or 
should this equally apply to anything that is connected to this SDIO 
Host Controller?

To give a bit more background:

I have an embedded board with a brcm_fmac WiFi module. It seems that due 
to a hardware limitation we are not permitted to switch the module off. 
It simply cannot be re-probed afterwards.

The property `keep-power-in-suspend` was used and that used to work fine 
until 92caded ("brcmfmac: Avoid keeping power to SDIO card
unless WOWL is used"), which made the wifi adapter by default turn off 
on suspend to be re-probed on resume. Not working on our board...


I have also looked at other WiFi drivers with an SDIO interface and it 
seems that none of them are really honoring the `keep-power-in-suspend` 
flag. Is this flag for the SDIO Host Controller only?


What would be proper way to implement it so that the brcm_fmac return to 
its old behaviour if necessary?
Add a Device Tree property directly for the brcm_fmac driver..?

I would like to write a patch, but I would like to know in which 
direction to go.


Thank you for any feedback

Matthias