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

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Date:   Mon, 11 Nov 2019 05:18:57 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     Jason Gunthorpe <jgg@...pe.ca>, 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

> -----Original Message-----
> From: kvm-owner@...r.kernel.org <kvm-owner@...r.kernel.org> On Behalf
> Of Jakub Kicinski
> Sent: Sunday, November 10, 2019 9:46 PM
> On Sun, 10 Nov 2019 10:18:55 +0100, gregkh@...uxfoundation.org wrote:

[..]
> The nice thing about having a fake bus is you can load out-of-tree drivers to
> operate extra protocols quite cleanly.
> 
This series does NOT intent to do any out of tree driver.
Please do not think in that direction for this series.

> I'm not saying that's what the code in question is doing, I'm saying I'd
> personally like to understand the motivation more clearly before every
> networking driver out there starts spawning buses. The only argument I've
> heard so far for the separate devices is reloading subset of the drivers, which
> I'd rate as moderately convincing.

Primary objectives behind using a bus in this series is:

1. get same level of device view as PF/VF/SF by devlink instance
2. to not re-invent already matured pm (suspend/resume) in devlink and/or vendor driver
3. ability to bind a sub-function to different drivers depending on use case based on 'in-kernel' defined class-id
(mdev/virtio/kernel) - just like vfio-pci and regular PF driver, by following standard driver model
(Ofcourse, It can be done using 3 or more buses as one virtual mdev bus appears an abuse)
4. create->configure->bind process of an sub function (just like a VF)
5. persistent naming of sf's netdev and rdmadev (again like PF and VF)

I will wait for Jason's and Jiri's view on the alternative proposal I sent few hours back to omit bus for in-kernel use of sf; and see how far can we run without a bus :-)