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

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Date:   Wed, 12 Jan 2022 10:24:29 -0800
From:   Tim Harvey <tharvey@...eworks.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Martin Schiller <ms@....tdt.de>, Hauke Mehrtens <hauke@...ke-m.de>,
        martin.blumenstingl@...glemail.com,
        Florian Fainelli <f.fainelli@...il.com>, hkallweit1@...il.com,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        David Miller <davem@...emloft.net>, kuba@...nel.org,
        netdev <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v6] net: phy: intel-xway: Add RGMII internal
 delay configuration

On Wed, Jan 12, 2022 at 5:14 AM Andrew Lunn <andrew@...n.ch> wrote:
>
> > > If I add a 'genphy_soft_reset(phydev);' at the top of
> > > xway_gphy_rgmii_init before the write to XWAY_MDIO_MIICTRL the values
> > > do take effect so perhaps that's the proper fix.
> >
> > OK, I see that we have to change something here.
> > But I would like to avoid a complete reset (BMCR_RESET) if possible.
>
> What does the datasheet say about BMCR_RESET? Some PHYs, like Marvell,
> it only resets the internal state machines. Register values are not
> changed back to defaults or anything like that. Also for many register
> writes in Marvell PHYs the write does not take effect until the next
> reset.
>
> So a BMCR_RESET can be the correct thing to do.
>

Andrew,

Datasheet [1] says "Resets the PHY to its default state. Active links
are terminated. Note that this is a self-clearing bit which is set to
zero by the hardware after reset has been done. See also IEEE
802.3-2008 22.2.4.1.1."

Experimentally I can change the delays and read them back as such,
then issue a BMCR_RESET and read them and they revert to strapped
values so I know BMCR_RESET resets at least some of the registers.

I suppose something to force auto-negotiation to occur again
(BMCR_ANEN?) would suffice. I'm not sure what the best course of
action is.

Tim
[1] https://assets.maxlinear.com/web/documents/618152_gpy111_pef7071vv16_hd_rev1.5.pdf