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

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Date:   Mon, 1 Feb 2021 17:06:58 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Saleem, Shiraz" <shiraz.saleem@...el.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        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>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        "Patil, Kiran" <kiran.patil@...el.com>
Subject: Re: [PATCH 07/22] RDMA/irdma: Register an auxiliary driver and
 implement private channel OPs

On Mon, Feb 1, 2021 at 4:40 PM Saleem, Shiraz <shiraz.saleem@...el.com> wrote:
>
> > Subject: Re: [PATCH 07/22] RDMA/irdma: Register an auxiliary driver and
> > implement private channel OPs
> >
> > On Sat, Jan 30, 2021 at 01:19:36AM +0000, Saleem, Shiraz wrote:
> > > > Subject: Re: [PATCH 07/22] RDMA/irdma: Register an auxiliary driver
> > > > and implement private channel OPs
> > > >
> > > > On Wed, Jan 27, 2021 at 07:16:41PM -0400, Jason Gunthorpe wrote:
> > > > > On Wed, Jan 27, 2021 at 10:17:56PM +0000, Saleem, Shiraz wrote:
> > > > >
> > > > > > Even with another core PCI driver, there still needs to be
> > > > > > private communication channel between the aux rdma driver and
> > > > > > this PCI driver to pass things like QoS updates.
> > > > >
> > > > > Data pushed from the core driver to its aux drivers should either
> > > > > be done through new callbacks in a struct device_driver or by
> > > > > having a notifier chain scheme from the core driver.
> > > >
> > > > Right, and internal to driver/core device_lock will protect from
> > > > parallel probe/remove and PCI flows.
> > > >
> > >
> > > OK. We will hold the device_lock while issuing the .ops callbacks from core
> > driver.
> > > This should solve our synchronization issue.
> > >
> > > There have been a few discussions in this thread. And I would like to
> > > be clear on what to do.
> > >
> > > So we will,
> > >
> > > 1. Remove .open/.close, .peer_register/.peer_unregister 2. Protect ops
> > > callbacks issued from core driver to the aux driver with device_lock
> >
> > A notifier chain is probably better, honestly.
> >
> > Especially since you don't want to split the netdev side, a notifier chain can be
> > used by both cases equally.
> >
>
> The device_lock seems to be a simple solution to this synchronization problem.
> May I ask what makes the notifier scheme better to solve this?
>

Only loosely following the arguments here, but one of the requirements
of the driver-op scheme is that the notifying agent needs to know the
target device. With the notifier-chain approach the target device
becomes anonymous to the notifier agent.