netdev - RE: [net-next 1/1] virtual-bus: Implementation of Virtual Bus

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Date:   Wed, 13 Nov 2019 07:03:40 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        Dave Ertman <david.m.ertman@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "sassmann@...hat.com" <sassmann@...hat.com>,
        "jgg@...pe.ca" <jgg@...pe.ca>, Kiran Patil <kiran.patil@...el.com>
Subject: RE: [net-next 1/1] virtual-bus: Implementation of Virtual Bus

Hi Greg, Jason,

> From: Greg KH <gregkh@...uxfoundation.org>
> Sent: Tuesday, November 12, 2019 3:28 PM
> > From: Dave Ertman <david.m.ertman@...el.com>
> >
> > This is the initial implementation of the Virtual Bus, virtbus_device
> > and virtbus_driver.  The virtual bus is a software based bus intended
> > to support lightweight devices and drivers and provide matching
> > between them and probing of the registered drivers.
> >
> > Files added:
> > 	drivers/bus/virtual_bus.c
> > 	include/linux/virtual_bus.h
> > 	Documentation/driver-api/virtual_bus.rst
> >
> > The primary purpose of the virual bus is to provide matching services
> > and to pass the data pointer contained in the virtbus_device to the
> > virtbus_driver during its probe call.  This will allow two separate
> > kernel objects to match up and start communication.
> >
> > The bus will support probe/remove shutdown and suspend/resume
> > callbacks.
> >
> > Kconfig and Makefile alterations are included
> >

[..]

I have a basic question with this bus.
I read device-driver model [1] few times but couldn't get the clarity.

mlx5_core driver will create virtbus device on virtbus.
mlx5_ib driver binds to virtbus device in probe().
However mlx5_ib driver's probe() will create rdma device whose parent device will be PCI device and not virtbus_device.
Is that correct?

If so, bus driver of bus A, creating devices binding to device of bus B (pci) adheres to the linux device model?
If so, such cross binding is not just limited to virtbus, right?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/driver-api/driver-model