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

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Date:   Tue, 26 Jan 2021 07:29:14 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Jacob Keller <jacob.e.keller@...el.com>
Cc:     "Saleem, Shiraz" <shiraz.saleem@...el.com>,
        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

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.

Thanks