linux-kernel - Re: [PATCH net-next v1 1/3] net: phy: micrel: add MDI/MDI-X control support for KSZ9477 switch-integrated PHYs

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Message-ID: <df3f4f74-50cc-42b2-8b41-913d4bcd211c@lunn.ch>
Date: Tue, 10 Jun 2025 15:12:54 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	kernel@...gutronix.de, linux-kernel@...r.kernel.org,
	Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v1 1/3] net: phy: micrel: add MDI/MDI-X control
 support for KSZ9477 switch-integrated PHYs

On Tue, Jun 10, 2025 at 02:46:11PM +0200, Oleksij Rempel wrote:
> On Tue, Jun 10, 2025 at 02:31:45PM +0200, Andrew Lunn wrote:
> > On Tue, Jun 10, 2025 at 11:13:52AM +0200, Oleksij Rempel wrote:
> > > Add MDI/MDI-X configuration support for PHYs integrated in the KSZ9477
> > > family of Ethernet switches.
> > > 
> > > All MDI/MDI-X configuration modes are supported:
> > >   - Automatic MDI/MDI-X (ETH_TP_MDI_AUTO)
> > >   - Forced MDI (ETH_TP_MDI)
> > >   - Forced MDI-X (ETH_TP_MDI_X)
> > > 
> > > However, when operating in automatic mode, the PHY does not expose the
> > > resolved crossover status (i.e., whether MDI or MDI-X is active).
> > > Therefore, in auto mode, the driver reports ETH_TP_MDI_INVALID as
> > > the current status.
> > 
> > I assume you also considered returning ETH_TP_MDI_AUTO? What makes
> > INVALID better than AUTO?
> 
> The phydev->mdix_ctrl returns configuration state, which cant be set to
> ETH_TP_MDI_AUTO.
> The phydev->mdix should return actual crossover state, which is
> ETH_TP_MDI or ETH_TP_MDI_X. Setting it to ETH_TP_MDI_AUTO, would not
> provide any usable information.

[Goes and looks at the code]

#define ETH_TP_MDI_INVALID	0x00 /* status: unknown; control: unsupported */
#define ETH_TP_MDI		0x01 /* status: MDI;     control: force MDI */
#define ETH_TP_MDI_X		0x02 /* status: MDI-X;   control: force MDI-X */
#define ETH_TP_MDI_AUTO		0x03 /*                  control: auto-select */

So _AUTO is not listed as being valid as a status. And _INVALID has
the comment unkown. So:

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew