Re: [PATCH 5/10] dt: bindings: Add bindings for Marvell Xenon SD Host Controller

From: Arnd Bergmann
Date: Thu Nov 24 2016 - 04:12:23 EST

On Thursday, November 24, 2016 10:05:45 AM CET Ulf Hansson wrote:
> > You also mentioned other bindings using child nodes, but for this one
> > we have one controller with only one set of register with multiple slots
> > (Atmel is an example). Here each slot have it own set of register.
> >
> > Actually giving the fact that each slot is controlled by a different set
> > of register I wonder why the hardware can't also deduce the slot number
> > from the address register. For me it looks like an hardware bug but we
> > have to deal with it.
> >
> > Do you still think we needchild node here?
> Using child-nodes for slots like what's done in the atmel case, is
> currently broken. I would recommend to avoid using child-nodes for
> slots, if possible.
> To give you some more background, currently the mmc core treats child
> nodes as embedded non-removable cards or SDIO funcs. However, we can
> change to make child-nodes also allowed to describe slots, but it
> requires a specific compatible for "slots" and of course then we also
> need to update the DT parsing of the child-nodes in the mmc core.
> Documentation/devicetree/bindings/mmc/mmc.txt
> Documentation/devicetree/bindings/mmc/mmc-card.txt

I don't see anything wrong with having child nodes for the slots
even with the current binding, under one condition:

The mmc.txt binding above must refer only to the child node, while
the parent node conceptually becomes a plain bus or MFD that
happens to encapsulate multiple MMC host controllers, and possibly
provides some shared registers to them.