linux-kernel - Re: [PATCH v1] ethtool: provide UAPI for PHY master/slave configuration.

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Date:   Wed, 15 Apr 2020 15:37:28 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Kubecek <mkubecek@...e.cz>,
        David Jander <david@...tonic.nl>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Russell King <linux@...linux.org.uk>, mkl@...gutronix.de
Subject: Re: [PATCH v1] ethtool: provide UAPI for PHY master/slave
 configuration.

On Wed, Apr 15, 2020 at 03:11:04PM +0200, Andrew Lunn wrote:
> On Wed, Apr 15, 2020 at 02:12:09PM +0200, Oleksij Rempel wrote:
> > This UAPI is needed for BroadR-Reach 100BASE-T1 devices. Due to lack of
> > auto-negotiation support, we needed to be able to configure the
> > MASTER-SLAVE role of the port manually or from an application in user
> > space.
> 
> Hi Oleksij
> 
> This is a nice way to do this.
> 
> > +/* Port mode */
> > +#define PORT_MODE_MASTER	0x00
> > +#define PORT_MODE_SLAVE		0x01
> > +#define PORT_MODE_MASTER_FORCE	0x02
> > +#define PORT_MODE_SLAVE_FORCE	0x03
> > +#define PORT_MODE_UNKNOWN	0xff
> 
> It is not clear to me what PORT_MODE_MASTER and PORT_MODE_SLAVE. Do
> these mean to negotiate master/slave? Maybe some comments, or clearer
> names?

In the IEEE 802.3 it is described as:
---------------------------------------------------------------------------
Port type: Bit 9.10 is to be used to indicate the preference to operate
as MASTER (multiport device) or as SLAVE (single-port device) if the
MASTER-SLAVE Manual Configuration Enable bit, 9.12, is not set.  Usage
of this bit is described in 40.5.2.
1 = Multiport device
0 = single-port device
---------------------------------------------------------------------------

Setting PORT_MODE_MASTER/PORT_MODE_SLAVE will increase the chance to get
MASTER or SLAVE mode, but not force it.

If we will follow strictly to the IEEE 802.3 spec, it should be named:

#define PORT_MODE_UNKNOWN	0x00
/* this two options will not force some specific mode, only influence
 * the chance to get it */
#define PORT_TYPE_MULTI_PORT	0x01
#define PORT_TYPE_SINGLE_PORT	0x02
/* this two options will force master or slave mode */
#define PORT_MODE_MASTER	0x03
#define PORT_MODE_SLAVE		0x04

Please tell, if you have better ideas.

Regards,
Oleksij
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