linux-kernel - Re: [PATCH net-next v6] net: phy: intel-xway: Add RGMII internal delay configuration

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Date:   Wed, 22 Feb 2023 17:04:25 +0100
From:   Michael Walle <michael@...le.cc>
To:     tharvey@...eworks.com
Cc:     andrew@...n.ch, davem@...emloft.net, f.fainelli@...il.com,
        hauke@...ke-m.de, hkallweit1@...il.com, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux@...linux.org.uk,
        martin.blumenstingl@...glemail.com, ms@....tdt.de,
        netdev@...r.kernel.org, Michael Walle <michael@...le.cc>
Subject: Re: [PATCH net-next v6] net: phy: intel-xway: Add RGMII internal delay configuration

Hi Tim, Hi Martin,

> I've got some boards with the GPY111 phy on them and I'm finding that
> modifying XWAY_MDIO_MIICTRL to change the skew has no effect unless I
> do a soft reset (BCMR_RESET) first. I don't see anything in the
> datasheet which specifies this to be the case so I'm interested it
> what you have found. Are you sure adjusting the skews like this
> without a soft (or hard pin based) reset actually works?

I do have the same PHY and I'm puzzled with the delay settings. Do
you have an EEPROM attached to the PHY? According to my datasheet,
that seems to make a difference. Apparently, only if there is an
EEPROM, you can change the value (the value is then also written to
the EEPROM according the datasheet).
If you don't have one, the values will get overwritten by the
external strappings on a soft reset. Therefore, it seems they cannot
be set. (FWIW there is also a sticky bit, but that doesn't seem to
help in this case).

-michael