netdev - Re: [RFC PATCH v5 01/16] RDMA/irdma: Add driver framework definitions

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Message-ID: <20200423190327.GC26002@ziepe.ca>
Date:   Thu, 23 Apr 2020 16:03:28 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     "Saleem, Shiraz" <shiraz.saleem@...el.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Ismail, Mustafa" <mustafa.ismail@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "sassmann@...hat.com" <sassmann@...hat.com>,
        "Patil, Kiran" <kiran.patil@...el.com>,
        "Ertman, David M" <david.m.ertman@...el.com>
Subject: Re: [RFC PATCH v5 01/16] RDMA/irdma: Add driver framework definitions

On Thu, Apr 23, 2020 at 05:15:22PM +0000, Saleem, Shiraz wrote:
> > Subject: Re: [RFC PATCH v5 01/16] RDMA/irdma: Add driver framework
> > definitions
> > 
> > On Thu, Apr 23, 2020 at 12:32:48AM +0000, Saleem, Shiraz wrote:
> > 
> > > we have a split initialization design for gen2 and future products.
> > > phase1 is control path resource initialization in irdma_probe_dev and
> > > phase-2 is the rest of the resources with the ib registration at the
> > > end of irdma_open. irdma_close must de-register the ib device which
> > > will take care of ibdev free too. So it makes sense to keep allocation
> > > of the ib device in irdma_open.
> > 
> > The best driver pattern is to allocate the ib_device at the very start of probe() and
> > use this to anchor all the device resources and memories.
> > 
> > The whole close/open thing is really weird, you should get rid of it.
> maybe I missing something. But why is it weird?

Because the RDMA driver should exist as its own entity. It does not
shutdown unless the remove() method on is struct device_driver is
closed.

So what exactly are open/cose supposed to be doing? I think it is a
left over of trying to re-implement the driver model.

> underlying configuration changes and reset management for the physical
> function need a light-weight mechanism which is realized with the close/open
> from netdev PCI drv --> rdma drv.

> Without a teardown and re-add of virtual device off the bus.

Yes, that is exactly right. If you have done something so disruptive
that the ib_device needs to be destroyed then you should unplug/replug
the entire virtual bus device, that is the correct and sane thing to
do. There is no 'light weight' here, destroying the ib_device is
incredibly expensive and disruptive.

Jason