netdev - Re: [PATCH net-next 5/5] arm64: dts: zynqmp: Add ZCU104 based TSN endpoint

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Message-ID: <CAL_JsqK9OvwicCbckvpk4CMWbhcP8yDBXAW_7CmLzR__-fJf0Q@mail.gmail.com>
Date:   Tue, 27 Jul 2021 14:17:57 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Michal Simek <michal.simek@...inx.com>,
        netdev <netdev@...r.kernel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next 5/5] arm64: dts: zynqmp: Add ZCU104 based TSN endpoint

On Tue, Jul 27, 2021 at 2:11 PM Gerhard Engleder
<gerhard@...leder-embedded.com> wrote:
>
> On Tue, Jul 27, 2021 at 1:41 AM Rob Herring <robh+dt@...nel.org> wrote:
> > > +       compatible = "engleder,zynqmp-tsnep", "xlnx,zynqmp-zcu104-revC",
> > > +                    "xlnx,zynqmp-zcu104", "xlnx,zynqmp";
> >
> > I don't think this will pass schema validation.
>
> You are right. I did rerun the validation and now I see the error.
>
> > In general, do we need a new top-level compatible for every possible
> > FPGA image? Shouldn't this be an overlay?
>
> All the devices I have dealt with so far had just a single FPGA image.
> There were no dynamic selection of the FPGA image or partial
> reconfiguration of the FPGA. So the FPGA image could be seen as part
> of the schematics. In this case the FPGA image stuff shall be in the
> device tree of the device. For me the question is: Does this combination
> of evaluation boards with its own FPGA image form a new device?
>
> The evaluation platform is based on ZCU104. The difference is not
> only the FPGA image. Also a FMC extension card with Ethernet PHYs is
> needed. So also the physical hardware is different.

Okay, that's enough of a reason for another compatible. You'll have to
update the schema.

> From my point of view it is a separate hardware platform with its own
> device tree. It's purpose is to show two tsnep Ethernet controllers in
> action. So far it worked good for me to see the FPGA image as part of
> the schematics like the list of devices on the SPI bus. No special handling
> just because an FPGA is used, which in the end is not relevant for the
> software because software cannot and need not differentiate between
> normal hardware and FPGA based hardware.
>
> But I also understand the view of just another FPGA image for an existing
> hardware.
>
> My goal is to get all necessary stuff, which is needed to run the evaluation
> platform, into mainline. I must confess, I have not thought about using an
> overlay. Is it right that overlays are not part of the kernel tree?

There's some work in progress on it. We can build and apply overlays
at build time now, but we haven't added any overlays under /arch.

Given the overall h/w is different, it doesn't seem like overlay will
buy you anything here.

Rob