netdev - Re: [PATCH net] net: dsa: microchip: keep compatibility with device tree blobs with no phy-mode

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Date:   Thu, 18 Aug 2022 15:21:07 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Russell King <rmk+kernel@...linux.org.uk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Woojung Huh <woojung.huh@...rochip.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Alvin ┼áipraga <alsi@...g-olufsen.dk>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Craig McQueen <craig@...ueen.id.au>
Subject: Re: [PATCH net] net: dsa: microchip: keep compatibility with device
 tree blobs with no phy-mode

On Thu, Aug 18, 2022 at 05:13:51PM +0200, Andrew Lunn wrote:
> > It is important to note that phy_device_create() initializes
> > dev->interface = PHY_INTERFACE_MODE_GMII, and so, when we use
> > phylink_create(PHY_INTERFACE_MODE_NA), no one will override this, and we
> > will end up with a PHY_INTERFACE_MODE_GMII interface inherited from the
> > PHY.
> 
> Is this actually a bug?
> 
> With pure phylib, you should call one of the connect functions, which
> underneath calls phy_attach_direct() which has a phy_interface_t. So
> the default in practice does not matter.

What do you consider "bug"? I think here is where phylink inherits what
phy_device_create() set as default:

int phylink_connect_phy(struct phylink *pl, struct phy_device *phy)
{
	int ret;

	/* Use PHY device/driver interface */
	if (pl->link_interface == PHY_INTERFACE_MODE_NA) {
		pl->link_interface = phy->interface;
		pl->link_config.interface = pl->link_interface; <- here
	}

	ret = phylink_attach_phy(pl, phy, pl->link_interface); <- here is the phy_attach_direct()
	if (ret < 0)
		return ret;

	ret = phylink_bringup_phy(pl, phy, pl->link_config.interface);
	if (ret)
		phy_detach(phy);

	return ret;
}

So yes, although you're right in that if you call phy_attach_direct()
this doesn't happen, but if you go through phylink_connect_phy() I think
it's expected that it will.

> > All this means that in order to maintain compatibility with device tree
> > blobs where the phy-mode property is missing, we need to allow the
> > "gmii" phy-mode and treat it as "internal".
> 
> of_get_phy_mode() returns PHY_INTERFACE_MODE_NA if the property is
> missing, which also suggests this is a bug.
> 
> I wonder if we have any ports which actually rely on
> PHY_INTERFACE_MODE_GMII?

What do you mean, you mean actual GMII wired to chip pinout?