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

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Message-ID: <CA+sq2CdrNDDhsfHoGiXzrJgfUXirEZjkxYcBOvi07jvJgtnnHQ@mail.gmail.com>
Date:   Fri, 31 Aug 2018 22:55:25 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, olof@...om.net,
        LAKML <linux-arm-kernel@...ts.infradead.org>,
        linux-soc@...r.kernel.org, Aleksey Makarov <amakarov@...vell.com>,
        Sunil Goutham <sgoutham@...vell.com>,
        Lukasz Bartosik <lbartosik@...vell.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 04/15] soc: octeontx2: Add mailbox support infra

On Fri, Aug 31, 2018 at 7:46 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> 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

Good point, thanks for catching this.
Will look into this and post a v2 series.

Thanks,
Sunil.