linux-kernel - Re: [RFC PATCH v2 8/8] arm64: dts: sparx5: Add the Sparx5 switch node

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Message-ID: <20201223143124.tr2vejqgpf2qsot2@mchp-dev-shegelun>
Date:   Wed, 23 Dec 2020 15:31:24 +0100
From:   Steen Hegelund <steen.hegelund@...rochip.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Device Tree List <devicetree@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        "Lars Povlsen" <lars.povlsen@...rochip.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Mark Einon <mark.einon@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v2 8/8] arm64: dts: sparx5: Add the Sparx5 switch node

On 19.12.2020 21:24, Andrew Lunn wrote:
>EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>
>> +             port13: port@13 {
>> +                     reg = <13>;
>> +                     /* Example: CU SFP, 1G speed */
>> +                     max-speed = <10000>;
>
>One too many 0's for 1G.

Ah, but this is allocation for the port, not the speed.  This just
used by the calendar module to allocate slots on the taxis as requested.
So I would say it is OK to overallocate in this case (but you could
argue it does not make much sense).

>
>> +             /* 25G SFPs */
>> +             port56: port@56 {
>> +                     reg = <56>;
>> +                     max-speed = <10000>;
>
>Why limit a 25G SFP to 10G?

In the PCB134 case it is to keep the total allocation below 200Gbits
((12+8)*10G).  There is a port mux mode that provides 8*25G on the 25G
SerDes'es, but that would be a different DT.

The Datasheet shows which port mux combinations are possible, and not
all combinations of SerDes, Speed and interface are allowed.

The PCB134 was designed to showcase this "many 10G ports" mode, so that
is why we have the current DT.

>
>    Andrew

BR
Steen

---------------------------------------
Steen Hegelund
steen.hegelund@...rochip.com