netdev - Re: [PATCH 3/4] net: dsa: microchip: Disable RGMII in-band status on KSZ9893

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Date:   Sat, 5 Sep 2020 16:53:20 +0100
From:   Paul Barker <pbarker@...sulko.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Woojung Huh <woojung.huh@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 3/4] net: dsa: microchip: Disable RGMII in-band status on KSZ9893

On Sat, 5 Sep 2020 at 16:32, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Sat, Sep 05, 2020 at 03:03:24PM +0100, Paul Barker wrote:
> > We can't assume that the link partner supports the in-band status
> > reporting which is enabled by default on the KSZ9893 when using RGMII
> > for the upstream port.
>
> What do you mean by RGMII inband status reporting? SGMII/1000BaseX has
> in band signalling, but RGMII?
>
>    Andrew

I'm referencing page 56 of the KSZ9893 datasheet
(http://ww1.microchip.com/downloads/en/DeviceDoc/KSZ9893R-Data-Sheet-DS00002420D.pdf).
The datasheet says "The RGMII port will not function properly if IBS
is enabled in the switch, but it is not receiving in-band status from
a connected PHY." Since we can't guarantee all possible link partners
will support this it should be disabled. In particular, the IMX6 SoC
we're using with this switch doesn't support this on its Ethernet
port.

I don't really know much about how this is implemented or how widely
it's supported.

Thanks,

-- 
Paul Barker
Konsulko Group