linux-kernel - Re: [PATCH v3 11/11] arm64: dts: Add Pensando Elba SoC support

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Date:   Mon, 8 Nov 2021 12:01:35 -0800
From:   Brad Larson <brad@...sando.io>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Mark Brown <broonie@...nel.org>,
        Serge Semin <fancer.lancer@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Olof Johansson <olof@...om.net>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 11/11] arm64: dts: Add Pensando Elba SoC support

On Mon, Nov 8, 2021 at 11:54 AM Marc Zyngier <maz@...nel.org> wrote:
> >
> > The Elba SoC is an embedded chip and not intended as a SBSA-compliant
> > general platform.
>
> This has nothing to do with following a standard. It has to do with
> following the intended use of the architecture. What you have here is
> the system architecture equivalent of trusting userspace to build the
> kernel page tables. It can work in limited cases. But would you want
> to deploy such construct at scale? Probably not.
>
> > In this implementation the ITS is used to provide message-based
> > interrupts for our (potentially large set) of hardware based
> > platform device instances.  Virtualization is not a consideration.
> > We don't have a SMMU.  Interrupt isolation isn't a practical
> > consideration for this product.
>
> Because you have foreseen all use cases for this HW ahead of time, and
> can already tell how SW is going to make use of it? Oh well...
>
> > Propose adding a comment to the dts.
> >
> > +                       /*
> > +                        * Elba SoC implemented a pre-ITS that happened to
> > +                        * be the same implementation as synquacer.
> > +                        */
>
> Which contains zero information. What you really want is: "We have
> decided to ignore the system architecture, good luck".
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.

On the contrary, the confusion of using the existing driver match
"socionext,synquacer-pre-its" is answered, why add new code.
Looks like we are deviating from the norm ;-).  I'm not seeing how
this conversation is a productive use of time for a platform in
production.

Thanks,
Brad