netdev - RE: [PATCH 07/22] RDMA/irdma: Register an auxiliary driver and implement private channel OPs

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Date:   Wed, 27 Jan 2021 01:02:39 +0000
From:   "Saleem, Shiraz" <shiraz.saleem@...el.com>
To:     "Keller, Jacob E" <jacob.e.keller@...el.com>,
        Leon Romanovsky <leon@...nel.org>
CC:     Jason Gunthorpe <jgg@...dia.com>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Ertman, David M" <david.m.ertman@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "Ismail, Mustafa" <mustafa.ismail@...el.com>,
        "jiri@...dia.com" <jiri@...dia.com>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: RE: [PATCH 07/22] RDMA/irdma: Register an auxiliary driver and
 implement private channel OPs

> Subject: Re: [PATCH 07/22] RDMA/irdma: Register an auxiliary driver and
> implement private channel OPs
> 
> 
> 
> On 1/25/2021 9:29 PM, Leon Romanovsky wrote:
> > On Mon, Jan 25, 2021 at 05:01:40PM -0800, Jacob Keller wrote:
> >>
> >>
> >> On 1/25/2021 4:39 PM, Saleem, Shiraz wrote:
> >>>> Subject: Re: [PATCH 07/22] RDMA/irdma: Register an auxiliary driver
> >>>> and implement private channel OPs
> >>>>
> >>>> On Sun, Jan 24, 2021 at 03:45:51PM +0200, Leon Romanovsky wrote:
> >>>>> On Fri, Jan 22, 2021 at 05:48:12PM -0600, Shiraz Saleem wrote:
> >>>>>> From: Mustafa Ismail <mustafa.ismail@...el.com>
> >>>>>>
> >>>>>> Register irdma as an auxiliary driver which can attach to
> >>>>>> auxiliary RDMA devices from Intel PCI netdev drivers i40e and
> >>>>>> ice. Implement the private channel ops, add basic devlink support
> >>>>>> in the driver and register net notifiers.
> >>>>>
> >>>>> Devlink part in "the RDMA client" is interesting thing.
> >>>>>
> >>>>> The idea behind auxiliary bus was that PCI logic will stay at one
> >>>>> place and devlink considered as the tool to manage that.
> >>>>
> >>>> Yes, this doesn't seem right, I don't think these auxiliary bus
> >>>> objects should have devlink instances, or at least someone from
> >>>> devlink land should approve of the idea.
> >>>>
> >>>
> >>> In our model, we have one auxdev (for RDMA) per PCI device function
> >>> owned by netdev driver and one devlink instance per auxdev. Plus there is an
> Intel netdev driver for each HW generation.
> >>> Moving the devlink logic to the PCI netdev driver would mean
> >>> duplicating the same set of RDMA params in each Intel netdev driver.
> >>> Additionally, plumbing RDMA specific params in the netdev driver sort of
> seems misplaced to me.
> >>>
> >>
> >> I agree that plumbing these parameters at the PCI side in the devlink
> >> of the parent device is weird. They don't seem to be parameters that
> >> the parent driver cares about.
> >>
> >> Maybe there is another mechanism that makes more sense? To me it is a
> >> bit like if we were plumbing netdev specific paramters into devlink
> >> instead of trying to expose them through netdevice specific
> >> interfaces like iproute2 or ethtool.
> >
> > I'm far from being expert in devlink, but for me separation is following:
> > 1. devlink - operates on physical device level, when PCI device already
> initialized.
> > 2. ethtool - changes needed to be done on netdev layer.
> > 3. ip - upper layer of the netdev
> > 4. rdmatool - RDMA specific when IB device already exists.
> >
> > And the ENABLE_ROCE/ENABLE_RDMA thing shouldn't be in the RDMA driver
> > at all, because it is physical device property which once toggled will
> > prohibit creation of respective aux device.
> >
> 
> Ok. I guess I hadn't looked quite as close at the specifics here. I agree that
> ENABLE_RDMA should go in the PF devlink.
> 
> If there's any other sort of RDMA-specific configuration that ties to the IB device,
> that should go somehow into rdmatool, rather than devlink. And thus: I think I
> agree, we don't want the IB device or the aux device to create a devlink instance.
> 

I think rdma-tool might be too late for this type of param. We need the protocol info (iWARP vs RoCE)
early on driver probe.