netdev - Re: [PATCH net-next v1 5/5] net: phy: micrel: ksz886x/ksz8081: add cabletest support

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Date:   Sat, 11 Jul 2020 20:29:12 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Philippe Schenker <philippe.schenker@...adex.com>
Subject: Re: [PATCH net-next v1 5/5] net: phy: micrel: ksz886x/ksz8081: add
 cabletest support

On Fri, Jul 10, 2020 at 02:08:51PM +0200, Oleksij Rempel wrote:
> This patch support for cable test for the ksz886x switches and the
> ksz8081 PHY.
> 
> The patch was tested on a KSZ8873RLL switch with following results:
> 
> - port 1:
>   - cannot detect any distance
>   - provides inverted values
>     (Errata: DS80000830A: "LinkMD does not work on Port 1",
>      http://ww1.microchip.com/downloads/en/DeviceDoc/KSZ8873-Errata-DS80000830A.pdf)
>     - Reports "short" on open or ok.
>     - Reports "ok" on short.
> 
> - port 2:
>   - can detect distance
>   - can detect open on each wire of pair A (wire 1 and 2)
>   - can detect open only on one wire of pair B (only wire 3)
>   - can detect short between wires of a pair (wires 1 + 2 or 3 + 6)
>   - short between pairs is detected as open.
>     For example short between wires 2 + 3 is detected as open.
> 
> In order to work around the errata for port 1, the ksz8795 switch driver
> should be extended to provide proper device tree support for the related
> PHY nodes. So we can set a DT property to mark the port 1 as affected by
> the errata.

Hi Oleksij

Do the PHY register read/writes pass through the DSA driver for the
8873?  I was wondering if the switch could intercept reads/writes on
port1 for KSZ8081_LMD and return EOPNOTSUPP? That would be a more
robust solution than DT properties, which are going to get forgotten.

      Andrew