[PATCH 0/6] Ancillary bus implementation and SOF multi-client support

[Parav Pandit]

Hi Pierre, Mark, Dan,

> From: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> Sent: Wednesday, October 7, 2020 10:12 PM
> 
> 
> >>> "virtual" here means "not real" :)
> >
> >> Which of these aux device use cases is not a real device? One of my
> >> planned usages for this facility is for the NPEM (Native PCIE
> >> Enclosure Management) mechanism that can appear on any PCIE
> >> bridge/endpoint. While it is true that the NPEM register set does not
> >> get its own PCI-b:d:f address on the host bus, it is still
> >> discoverable by a standard enumeration scheme. It is real auxiliary
> >> device functionality that can appear on any PCIE device where the
> >> kernel can now have one common NPEM driver for all instances in the
> >> topology.
> >
> > Some if not all of the SOF cases are entirely software defined by the
> > firmware downloaded to the audio DSPs.
> 
> Correct for DSP processing/debug stuff. In some cases though, the firmware
> deals with different IOs (HDMI, I2C) and having multiple 'aux'
> devices helps expose unrelated physical functions in a more modular way.
> 
> The non-SOF audio case I can think of is SoundWire. We want to expose
> SoundWire links as separate devices even though they are not exposed in
> the platform firmware or PCI configs (decision driven by Windows). We
> currently use platform devices for this, but we'd like to transition to this 'aux'
> bus

There is more updated version of the patch [1] from Dave which is covering multiple mailing list who are also going to consume this bus.
This includes 
(a) mlx5 subdevices for netdev, rdma and more carved from a pci device.
(b) mlx5 matching service to load multiple drivers on for a given PCI PF/VF/subfunction.
(similar use case as irdma)

Greg also mentioned that he likes to see other mailing list CCed, which Dave already did in PATCHv2 at [1].
So lets please discuss in thread [1]?

[1] https://lore.kernel.org/linux-rdma/20201005182446.977325-1-david.m.ertman@intel.com/