netdev - RE: [PATCH v2 net-next 7/8] net: dsa: microchip: Prepare PHY for proper advertisement

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Date:   Wed, 6 Dec 2017 21:55:26 +0000
From:   <Tristram.Ha@...rochip.com>
To:     <andrew@...n.ch>
CC:     <f.fainelli@...il.com>, <pavel@....cz>,
        <ruediger.schmitt@...lips.com>, <UNGLinuxDriver@...rochip.com>,
        <netdev@...r.kernel.org>
Subject: RE: [PATCH v2 net-next 7/8] net: dsa: microchip: Prepare PHY for
 proper advertisement

> > +static void ksz9477_phy_setup(struct ksz_device *dev, int port,
> > +			      struct phy_device *phy)
> > +{
> > +	if (port < dev->phy_port_cnt) {
> > +		/* SUPPORTED_Asym_Pause and SUPPORTED_Pause can be
> removed to
> > +		 * disable flow control when rate limiting is used.
> > +		 */
> > +		phy->advertising = phy->supported;
> > +	}
> 
> This looks a bit odd. phy_probe() does the same:
> 
>        /* Start out supporting everything. Eventually,
>          * a controller will attach, and may modify one
>          * or both of these values
>          */
>         phydev->supported = phydrv->features;
>         of_set_phy_supported(phydev);
>         phydev->advertising = phydev->supported;
> 
> You don't modify anything here, so i don't see why it is needed.
>

In my case I always see the value of advertising is 0x02ff, while that of
supported is 0x62ff.  The Cadence MAC I use does not support flow
control, so maybe the advertising value is stripped of that.

If I do not do anything flow control will not be enabled for the ports.
A device connected at 1000 Mbit and another connected at 100 Mbit
will have dropped packet issue if the switch does not do anything else
to regulate traffic.

For other switches that do not really support Asymmetric Pause it
has to be explicitly removed.

> > +void ksz_adjust_link(struct dsa_switch *ds, int port,
> > +		     struct phy_device *phydev)
> > +{
> > +	struct ksz_device *dev = ds->priv;
> > +	struct ksz_port *p = &dev->ports[port];
> > +
> > +	if (phydev->link) {
> > +		p->speed = phydev->speed;
> > +		p->duplex = phydev->duplex;
> > +		p->flow_ctrl = phydev->pause;
> > +		p->link_up = 1;
> > +		dev->live_ports |= (1 << port) & dev->on_ports;
> > +	} else if (p->link_up) {
> > +		p->link_up = 0;
> > +		p->link_down = 1;
> > +		dev->live_ports &= ~(1 << port);
> > +	}
> 
> The link_down looks odd. If you are setting link_up to 1, should
> link_down also be set to 0? Can it be both up and down at the same
> time?

These variables are used internally.  link_up is an indication of the link;
link_down means the link is just dropped.  It is used for MIB counter
reading.  When the link is down most of the MIB counters will not be
updated, so it is a waste of time to read them.  They still are read at
least one more time to pick up any updated counters.