Subject: Re: [RFC PATCH 09/16] dsa: dsa: Split up creating/destroying of DSA and CPU ports

From: Andrew Lunn <[email-masked]>
Date: Fri, 27 May 2016 17:07:44 +0200

On Fri, May 27, 2016 at 10:33:49AM -0400, Vivien Didelot wrote:
> Hi Andrew,
> 
> Andrew Lunn <[email-masked]> writes:
> 
> > -static void dsa_switch_destroy(struct dsa_switch *ds)
> > +void dsa_cpu_dsa_destroy(struct device_node *port_dn)
> >  {
> > -	struct device_node *port_dn;
> >  	struct phy_device *phydev;
> > +
> > +	if (of_phy_is_fixed_link(port_dn)) {
> > +		phydev = of_phy_find_device(port_dn);
> > +		if (phydev) {
> > +			phy_device_free(phydev);
> > +			fixed_phy_unregister(phydev);
> > +		}
> > +	}
> > +}
> > +
> > +static void dsa_switch_destroy(struct dsa_switch *ds)
> > +{
> >  	int port;
> >  
> >  #ifdef CONFIG_NET_DSA_HWMON
> > @@ -445,17 +467,11 @@ static void dsa_switch_destroy(struct dsa_switch *ds)
> >  		dsa_slave_destroy(ds->ports[port].netdev);
> >  	}
> >  
> > -	/* Remove any fixed link PHYs */
> > +	/* Disable configuration of the CPU and DSA ports */
> >  	for (port = 0; port < DSA_MAX_PORTS; port++) {
> > -		port_dn = ds->ports[port].dn;
> > -		if (of_phy_is_fixed_link(port_dn)) {
> > -			phydev = of_phy_find_device(port_dn);
> > -			if (phydev) {
> > -				phy_device_free(phydev);
> > -				of_node_put(port_dn);
> 
> Why does dsa_cpu_dsa_destroy drop that of_node_put call?

The of node reference counting is broken. The DT maintainers actually
say not to care, the whole reference counting scheme is broken. Which
is a bit sad really. There was a discussion about this a couple of
months ago.

Anyway, the reference is taken in dsa_of_probe() as part of the
or_each_available_child_of_node(child, port). This reference has
nothing to do with the port being a fixed link or not. So freeing it
here is inappropriate. The correct place to free it would probably be
in dsa_of_remove.
 
> > -				fixed_phy_unregister(phydev);
> > -			}
> > -		}
> > +		if ((dsa_is_cpu_port(ds, port) || dsa_is_dsa_port(ds, port)))
> > +			continue;
> 
> Why do we skip DSA and CPU ports here? The previous code didn't.
> 
> > +		dsa_cpu_dsa_destroy(ds->ports[port].dn);

They are now destroyed by the newly added dsa_cpu_dsa_destroy().  I'm
making the code more symmetrical and easier to re-use. The inverse of
this function is dsa_switch_setup_one() and it also uses a helper
function to setup the dsa and cpu ports, dsa_cpu_dsa_setups().

	 Andrew