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From:   Elad Nachman <enachman@marvell.com>
To:     Andrew Lunn <andrew@lunn.ch>
CC:     "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "krzysztof.kozlowski+dt@linaro.org" 
        <krzysztof.kozlowski+dt@linaro.org>,
        "conor+dt@kernel.org" <conor+dt@kernel.org>,
        "gregory.clement@bootlin.com" <gregory.clement@bootlin.com>,
        "sebastian.hesselbarth@gmail.com" <sebastian.hesselbarth@gmail.com>,
        "pali@kernel.org" <pali@kernel.org>,
        "mrkiko.rs@gmail.com" <mrkiko.rs@gmail.com>,
        "chris.packham@alliedtelesis.co.nz" 
        <chris.packham@alliedtelesis.co.nz>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Yuval Caduri <cyuval@marvell.com>
Subject: RE: [EXT] Re: [PATCH v6 3/3] arm64: dts: cn913x: add device trees for
 COM Express boards
Thread-Topic: [EXT] Re: [PATCH v6 3/3] arm64: dts: cn913x: add device trees
 for COM Express boards
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Date:   Wed, 29 Nov 2023 07:41:23 +0000
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> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Tuesday, November 28, 2023 12:34 AM
> To: Elad Nachman <enachman@marvell.com>
> Cc: robh+dt@kernel.org; krzysztof.kozlowski+dt@linaro.org;
> conor+dt@kernel.org; gregory.clement@bootlin.com;
> sebastian.hesselbarth@gmail.com; pali@kernel.org; mrkiko.rs@gmail.com;
> chris.packham@alliedtelesis.co.nz; devicetree@vger.kernel.org; linux-
> kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; Yuval Cadur=
i
> <cyuval@marvell.com>
> Subject: [EXT] Re: [PATCH v6 3/3] arm64: dts: cn913x: add device trees fo=
r
> COM Express boards
>=20
> External Email
>=20
> ----------------------------------------------------------------------
> > +++ b/arch/arm64/boot/dts/marvell/ac5x-rd-carrier-cn9131.dts
> > @@ -0,0 +1,25 @@
> > +// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
> > +/*
> > + * Copyright (C) 2023 Marvell International Ltd.
> > + *
> > + * Device tree for the AC5X RD Type 7 Com Express carrier board,
> > + * Utilizing the CN913x COM Express CPU module board.
> > + * This specific board only maintains a PCIe link with the CPU CPU
> > +module
> > + * module, which does not require any special DTS definitions.
> > + */
> > +
> > +#include "cn9131-db-comexpress.dtsi"
> > +#include "ac5x-rd-carrier.dtsi"
> > +
> > +/ {
> > +	model =3D "Marvell Armada AC5X RD COM EXPRESS type 7 carrier
> board with CN9131 CPU module";
> > +	compatible =3D "marvell,cn9131-ac5x-carrier", "marvell,rd-ac5x-
> carrier",
> > +			"marvell,cn9131-cpu-module", "marvell,cn9131",
> > +			"marvell,armada-ap807-quad", "marvell,armada-
> ap807";
>=20
> > diff --git a/arch/arm64/boot/dts/marvell/ac5x-rd-carrier.dtsi
> > b/arch/arm64/boot/dts/marvell/ac5x-rd-carrier.dtsi
> > new file mode 100644
> > index 000000000000..fd45d5582233
>=20
> > +/ {
> > +	model =3D "Marvell Armada AC5X RD COM EXPRESS type 7 carrier
> board";
> > +	compatible =3D "marvell,rd-ac5x-carrier";
>=20
> Now i'm confused. What does rd mean?
>=20
> I would expect RD mean Reference Design, and that is the complete device =
in
> its box.

AC5X RD can either work as you would expect, as a complete standalone box u=
sing the internal CPU, or you can move the switch on the back of the box to=
 "external" mode, and connect via an external cable a kit which would allow=
 it to use an external CPU COM Express module, mounted on top of an interpo=
ser kit.

>=20
> Yet, here you have RD for the carrier?
>=20
> The box itself is called cn9131-ac5x-carrier?
>=20
> This makes no sense to me.
>=20
> Maybe i'm understanding this all wrong, and its the carrier which you are
> producing a reference design for? The CPU module does not really matter? =
I

So in this case, once the switch is set to external as explained above, the=
 AC5X RD becomes part of the carrier solution.
This is a development/reference solution, not a full commercial solution, h=
ence it has the flexibility to be configured in different modes of operatio=
n.

> could use any off the shelf ComExpress 7 SOM. The bits you are trying to =
sell

Basically, yes. We have it validated versus few x86_64 system in our labs.

> are on the carrier? But since you are Marvell, you don't want to recommen=
d
> using an AMD ComExpress board when you happen to also have CPU

To the best of my knowledge, we did not validate specifically against AMD C=
OM Express solutions.
Since some of these modules utilize non-standard implementation of the COM =
Express standard (for example, few AMD CPUs do not have 10G signals, hence =
few AMD COM Express designs drive PCIe signals via the 10G-KR Ethernet pins=
 of the COM Express standard), it is up to the customer, if he chooses to u=
se such module(s), to validate them against the Marvell AC5X RD, acting as =
carrier via the interposer kit.

> module which would work? But the CPU is not really the point of this, its=
 the
> carrier?

We have tested and validated a complete reference/development solution comb=
ining CN9131 Com Express CPU module, interposer kit and AC5X RD as carrier.
We only push to upstream solutions which we have validated in the lab, henc=
e we push device tree files for the combination tested - specific CPU and s=
pecific carrier.
Customers are free to use other COM Express CPU modules, but they will have=
 to validate them by themselves, to account for any deviation from the COM =
Express standard.
After that, if they wish, they can choose to go for the process of upstream=
ing their device tree files by their own, like we chose.

>=20
> 	Andrew

FYI,

Elad.