On Mon, Jun 29, 2020 at 07:59:59PM -0300, Jason Gunthorpe wrote:

On Mon, Jun 29, 2020 at 09:33:17PM +0100, Mark Brown wrote:

quoted

On Wed, May 27, 2020 at 09:17:33AM +0200, Greg KH wrote:

quoted

quoted

Ok, that's good to hear.  But platform devices should never be showing
up as a child of a PCI device.  In the "near future" when we get the
virtual bus code merged, we can convert any existing users like this to
the new code.

quoted

What are we supposed to do with things like PCI attached FPGAs and ASICs
in that case?  They can have host visible devices with physical
resources like MMIO ranges and interrupts without those being split up
neatly as PCI subfunctions - the original use case for MFD was such
ASICs, there's a few PCI drivers in there now. 

Greg has been pretty clear that MFD shouldn't have been used on top of
PCI drivers.

The proposed bus lacks resource handling, an equivalent of
platform_get_resource() and friends for example, which would be needed
for use with physical devices.  Both that and the name suggest that it's
for virtual devices.

In a sense virtual bus is pretty much MFD v2.

Copying in Lee since I'm not sure he's aware of this, it's quite a
recent thing...  MFD is a layer above AFAICT, it's not a bus but rather
a combination of helpers for registering subdevices and a place for
drivers for core functionality of devices which have multiple features.

The reason the MFDs use platform devices is that they end up having to
have all the features of platform devices - originally people were
making virtual buses for them but the code duplication is real so
everyone (including Greg) decided to just use what was there already.