Re: [PATCH net-next v3 1/2] ethtool: provide UAPI for PHY master/slave configuration.

[Oleksij Rempel]

Hi Michal,

On Wed, Apr 29, 2020 at 09:52:22PM +0200, Michal Kubecek wrote:
> On Tue, Apr 28, 2020 at 09:53:07AM +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.
> > 
> > The same UAPI can be used for 1000BASE-T or MultiGBASE-T devices to
> > force MASTER or SLAVE role. See IEEE 802.3-2018:
> > 22.2.4.3.7 MASTER-SLAVE control register (Register 9)
> > 22.2.4.3.8 MASTER-SLAVE status register (Register 10)
> > 40.5.2 MASTER-SLAVE configuration resolution
> > 45.2.1.185.1 MASTER-SLAVE config value (1.2100.14)
> > 45.2.7.10 MultiGBASE-T AN control 1 register (Register 7.32)
> > 
> > The MASTER-SLAVE role affects the clock configuration:
> > 
> > -------------------------------------------------------------------------------
> > When the  PHY is configured as MASTER, the PMA Transmit function shall
> > source TX_TCLK from a local clock source. When configured as SLAVE, the
> > PMA Transmit function shall source TX_TCLK from the clock recovered from
> > data stream provided by MASTER.
> > 
> > iMX6Q                     KSZ9031                XXX
> > ------\                /-----------\        /------------\
> >       |                |           |        |            |
> >  MAC  |<----RGMII----->| PHY Slave |<------>| PHY Master |
> >       |<--- 125 MHz ---+-<------/  |        | \          |
> > ------/                \-----------/        \------------/
> >                                                ^
> >                                                 \-TX_TCLK
> > 
> > -------------------------------------------------------------------------------
> > 
> > Since some clock or link related issues are only reproducible in a
> > specific MASTER-SLAVE-role, MAC and PHY configuration, it is beneficial
> > to provide generic (not 100BASE-T1 specific) interface to the user space
> > for configuration flexibility and trouble shooting.
> > 
> > Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
> > ---
> [...]
> > diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
> > index 72c69a9c8a98a..a6a774beb2f90 100644
> > --- a/drivers/net/phy/phy.c
> > +++ b/drivers/net/phy/phy.c
> > @@ -285,6 +285,9 @@ int phy_ethtool_ksettings_set(struct phy_device *phydev,
> >  	      duplex != DUPLEX_FULL)))
> >  		return -EINVAL;
> >  
> > +	if (!ethtool_validate_master_slave_cfg(cmd->base.master_slave_cfg))
> > +		return -EINVAL;
> > +
> 
> Unless we can/want to pass extack down here, I would prefer to have the
> sanity check in ethtool_update_linkmodes() or ethtool_set_linkmodes() so
> that we can set meaningful error message and offending attribute in
> extack. (It could be even part of the policy.) Also, with the check only
> here, drivers/devices not calling phy_ethtool_set_link_ksettings()
> (directly or via phy_ethtool_set_link_ksettings()) and not handling the
> new members themselves would silently ignore any value from userspace.

ok

> >  	phydev->autoneg = autoneg;
> >  
> >  	phydev->speed = speed;
> [...]
> > +static int genphy_setup_master_slave(struct phy_device *phydev)
> > +{
> > +	u16 ctl = 0;
> > +
> > +	if (!phydev->is_gigabit_capable)
> > +		return 0;
> 
> Shouldn't we rather return -EOPNOTSUPP if value different from
> CFG_UNKNOWN was requested?

sounds plausible.

> > +
> > +	switch (phydev->master_slave_set) {
> > +	case PORT_MODE_CFG_MASTER_PREFERRED:
> > +		ctl |= CTL1000_PREFER_MASTER;
> > +		break;
> > +	case PORT_MODE_CFG_SLAVE_PREFERRED:
> > +		break;
> > +	case PORT_MODE_CFG_MASTER_FORCE:
> > +		ctl |= CTL1000_AS_MASTER;
> > +		/* fallthrough */
> > +	case PORT_MODE_CFG_SLAVE_FORCE:
> > +		ctl |= CTL1000_ENABLE_MASTER;
> > +		break;
> > +	case PORT_MODE_CFG_UNKNOWN:
> > +		return 0;
> > +	default:
> > +		phydev_warn(phydev, "Unsupported Master/Slave mode\n");
> > +		return 0;
> > +	}
> [...]
> > diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
> > index 92f737f101178..eb680e3d6bda5 100644
> > --- a/include/uapi/linux/ethtool.h
> > +++ b/include/uapi/linux/ethtool.h
> > @@ -1666,6 +1666,31 @@ static inline int ethtool_validate_duplex(__u8 duplex)
> >  	return 0;
> >  }
> >  
> > +/* Port mode */
> > +#define PORT_MODE_CFG_UNKNOWN		0
> > +#define PORT_MODE_CFG_MASTER_PREFERRED	1
> > +#define PORT_MODE_CFG_SLAVE_PREFERRED	2
> > +#define PORT_MODE_CFG_MASTER_FORCE	3
> > +#define PORT_MODE_CFG_SLAVE_FORCE	4
> > +#define PORT_MODE_STATE_UNKNOWN		0
> > +#define PORT_MODE_STATE_MASTER		1
> > +#define PORT_MODE_STATE_SLAVE		2
> > +#define PORT_MODE_STATE_ERR		3
> 
> You have "MASTER_SLAVE" or "master_slave" everywhere but "PORT_MODE" in
> these constants which is inconsistent.

What will be preferred name?

> > +
> > +static inline int ethtool_validate_master_slave_cfg(__u8 cfg)
> > +{
> > +	switch (cfg) {
> > +	case PORT_MODE_CFG_MASTER_PREFERRED:
> > +	case PORT_MODE_CFG_SLAVE_PREFERRED:
> > +	case PORT_MODE_CFG_MASTER_FORCE:
> > +	case PORT_MODE_CFG_SLAVE_FORCE:
> > +	case PORT_MODE_CFG_UNKNOWN:
> > +		return 1;
> > +	}
> > +
> > +	return 0;
> > +}
> 
> Should we really allow CFG_UNKNOWN in client requests? As far as I can
> see, this value is handled as no-op which should be rather expressed by
> absence of the attribute. Allowing the client to request a value,
> keeping current one and returning 0 (success) is IMHO wrong.

ok

> Also, should this function be in UAPI header?

It is placed together with other validate functions:
ethtool_validate_duplex
ethtool_validate_speed

Doing it in a different place, would be inconsistent.

> [...]
> > @@ -119,7 +123,12 @@ static int linkmodes_fill_reply(struct sk_buff *skb,
> >  	}
> >  
> >  	if (nla_put_u32(skb, ETHTOOL_A_LINKMODES_SPEED, lsettings->speed) ||
> > -	    nla_put_u8(skb, ETHTOOL_A_LINKMODES_DUPLEX, lsettings->duplex))
> > +	    nla_put_u8(skb, ETHTOOL_A_LINKMODES_DUPLEX, lsettings->duplex) ||
> > +	    nla_put_u8(skb, ETHTOOL_A_LINKMODES_MASTER_SLAVE_CFG,
> > +		       lsettings->master_slave_cfg) ||
> > +	    nla_put_u8(skb, ETHTOOL_A_LINKMODES_MASTER_SLAVE_STATE,
> > +		       lsettings->master_slave_state))
> > +
> >  		return -EMSGSIZE;
> 
> From the two handlers you introduced, it seems we only get CFG_UNKNOWN
> or STATE_UNKNOWN if driver or device does not support the feature at all
> so it would be IMHO more appropriate to omit the attribute in such case.

STATE_UNKNOWN is returned if link is not active.

Regards,
Oleksij
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