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 00:42:09 +0000
From:   "Saleem, Shiraz" <shiraz.saleem@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        "Keller, Jacob E" <jacob.e.keller@...el.com>
CC:     Leon Romanovsky <leon@...nel.org>,
        "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 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.
> 
> It does, the PCI driver is not supposed to spawn any aux devices for RDMA at all
> if RDMA is disabled.
> 
> For an iWarp driver I would consider ENABLE_ROCE to really be a general
> ENABLE_RDMA.

Well the driver supports iWARP and RoCE for E810 device.
Are you saying that this generic enable_roce devlink param really
is an enable 'rdma' traffic or not param?

> 
> Are you sure you need to implement this?

What we are after is some mechanism for user to switch the protocols iWARP vs RoCE
[default the device comes up as an iWARP dev]. The protocol info is really needed early-on
in the RDMA driver.probe(). i.e. when the rdma admin queue is created.

The same goes with the other param resource_limits_selector. It's a profile selector that a user
can chose to different # of max QP, CQs, MRs etc.

> 
> In any event, you just can't put the generic ENABLE_ROCE flag anyplace but the
> PCI device for devlink, it breaks the expected user API established by mlx5
> 
> Jason