netdev - Re: [PATCH net-next 00/19] Mellanox, mlx5 sub function support

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Date:   Sat, 9 Nov 2019 09:46:59 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Parav Pandit <parav@...lanox.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David M <david.m.ertman@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Or Gerlitz <gerlitz.or@...il.com>
Subject: Re: [PATCH net-next 00/19] Mellanox, mlx5 sub function support

On Fri, Nov 08, 2019 at 08:44:26PM -0400, Jason Gunthorpe wrote:
> There has been some lack of clarity on what the ?? should be. People
> have proposed platform and MFD, and those seem to be no-goes. So, it
> looks like ?? will be a mlx5_driver on a mlx5_bus, and Intel will use
> an ice_driver on a ice_bus, ditto for cxgb4, if I understand Greg's
> guidance.

Yes, that is the only way it can work because you really are just
sharing a single PCI device in a vendor-specific way, and they all need
to get along with each one properly for that vendor-specific way.  So
each vendor needs its own "bus" to be able to work out things properly,
I doubt you can make this more generic than that easily.

> Though I'm wondering if we should have a 'multi_subsystem_device' that
> was really just about passing a 'void *core_handle' from the 'core'
> (ie the bus) to the driver (ie RDMA, netdev, etc). 

Ick, no.

> It seems weakly defined, but also exactly what every driver doing this
> needs.. It is basically what this series is abusing mdev to accomplish.

What is so hard about writing a bus?  Last I tried it was just a few
hundred lines of code, if that.  I know it's not the easiest in places,
but we have loads of examples to crib from.  If you have
problems/questions, just ask!

Or, worst case, you just do what I asked in this thread somewhere, and
write a "virtual bus" where you just create devices and bind them to the
driver before registering and away you go.  No auto-loading needed (or
possible), but then you have a generic layer that everyone can use if
they want to (but you loose some functionality at the expense of
generic code.)

Are these constant long email threads a way that people are just trying
to get me to do this work for them?  Because if it is, it's working...

thanks,

greg k-h