Re: [Qemu-ppc] [PATCH v2 3/7] ppc/pnv: Add XSCOM infrastructure

[Benjamin Herrenschmidt]

On Wed, 2016-09-07 at 07:47 +1000, Benjamin Herrenschmidt wrote:
> d be an extra op in the xscom device model I guess. 
> 
> No. If you split the XSCOM bus from the MMIO -> XSCOM bridge (the
> ADU)
> then the conversion only happens in the former. You don't directly
> route the MMIOs over ! You intercept the MMIOs and use use the
> address_space_rw to "generate" the XSCOM accesses on the other side,
> like I do for the LPC bus.
> 
> We need that anyway because of the way XSCOMs can manipulate the HMER
> etc...
> 
> > 
> > Also, the main purpose of the XscomBus is to loop on the devices 
> > to populate the device tree. I am wondering if we could just use 
> > a simple list under the chip for that purpose.

In fact, if you do the above, you no longer need a XSCOM device...

A number of "devices" can exist below a chip, all they need to have
XSCOMs is to register memory regions that are child of that chip's
xscom_region.

For device-tree, well, we could have a generic interface that anything
that can populate DT has and iterate through them. Or make a "chiplet"
class or something.

Cheers,
Ben.