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

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Date:   Sun, 10 Nov 2019 10:16:29 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Parav Pandit <parav@...lanox.com>,
        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 Sat, Nov 09, 2019 at 12:18:09PM +0100, Jiri Pirko wrote:
> Sat, Nov 09, 2019 at 09:46:59AM CET, gregkh@...uxfoundation.org wrote:
> >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.)
> 
> Pardon my ignorance, just to be clear: You suggest to have
> one-virtual-bus-per-driver or rather some common "xbus" to serve this
> purpose for all of them, right?

Yes.

> If so, isn't that a bit ugly to have a bus in every driver?

No, not if that's what you want to have for that specific type of
device.  I.e. you want to have multiple drivers all attached to a single
PCI device and somehow "share" the physical resources properly in a sane
way.

> I wonder if there can be some abstraction found.

The abstraction is just that, the bus one.  It's not all that complex,
is it?

thanks,

greg k-h