netdev - Re: [PATCH 04/15] soc: octeontx2: Add mailbox support infra

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Date:   Fri, 31 Aug 2018 16:16:04 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Olof Johansson <olof@...om.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-soc@...r.kernel.org, amakarov@...vell.com,
        sgoutham@...vell.com, lbartosik@...vell.com,
        Networking <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH 04/15] soc: octeontx2: Add mailbox support infra

On Thu, Aug 30, 2018 at 8:37 PM Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
> On Thu, Aug 30, 2018 at 7:27 PM Arnd Bergmann <arnd@...db.de> wrote:
> > On Tue, Aug 28, 2018 at 3:23 PM Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
> > > On Tue, Aug 28, 2018 at 6:22 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > > On Tue, Aug 28, 2018 at 2:48 PM Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
> > > Any PCI device here irrespective in what domain (kernel or userspace)
> > > they are in
> > > use common mailbox communication. Which is
> > > # Write a mailbox msg (format is agreed between all parties) into
> > > shared (between AF and other PF/VFs)
> > >    memory region and trigger a interrupt to admin function.
> > > # Admin function processes the msg and puts reply in the same memory
> > > region and trigger
> > >    IRQ to the requesting device. If the device has a driver instance
> > > in kernel then it uses
> > >    IRQ and userspace applications does polling on the IRQ status bit.
> >
> > What is the purpose of the exported interface then? Is this
> > just an abstraction so each of the drivers can talk to its own
> > mailbox using a set of common helper functions?
> >
>
> Yes, that's correct.
>
> In kernel there will be a minimum of 3 drivers which will use this
> mailbox communication.
> So instead of duplicating APIs and structures in every driver, we
> thought of adding them in this AF driver and export them to ethernet
> and crypto drivers.

Ok. My feeling is then that the API is fine, but that it should not
be part of the AF module but rather be a standalone module.

My comment about the generic mailbox API no longer applies
here: you don't have a single shared mailbox hardware interface,
but each device has its own mailbox register set, so there
is no point in setting up a separate device for it, but I see
no need for creating an artificial dependency on the AF
driver. E.g. in a virtual machine that only has one ethernet
interface, you otherwise wouldn't load that driver, right?

         Arnd