Re: [PATCH net-next v5 11/13] net: lan966x: add PCIe FDMA XDP support

[Daniel Machon]

> On Wed, 20 May 2026 10:12:23 +0200 Daniel Machon wrote:
> >  #if IS_ENABLED(CONFIG_MCHP_LAN966X_PCI)
> >  extern const struct lan966x_fdma_ops lan966x_fdma_pci_ops;
> > +
> > +static inline bool lan966x_is_pci(struct lan966x *lan966x)
> > +{
> > +     return lan966x->ops == &lan966x_fdma_pci_ops;
> 
>         return IS_ENABLED(CONFIG_MCHP_LAN966X_PCI) &&
>                 lan966x->ops == &lan966x_fdma_pci_ops;
> 
> compiler will eliminate the reference to the ops as dead code
> and linker will not complain that its object is missing.

Ack. Will change in v6.

> 
> > +}
> > +#else
> > +static inline bool lan966x_is_pci(struct lan966x *lan966x)
> > +{
> > +     return false;
> > +}
> >  #endif
> >
> >  int lan966x_lag_port_join(struct lan966x_port *port,
> > diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c b/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
> > index 9ee61db8690b..b470f731e25c 100644
> > --- a/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
> > +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
> > @@ -24,6 +24,16 @@ static int lan966x_xdp_setup(struct net_device *dev, struct netdev_bpf *xdp)
> >       old_prog = xchg(&port->xdp_prog, xdp->prog);
> >       new_xdp = lan966x_xdp_present(lan966x);
> >
> > +     /* PCIe FDMA uses contiguous buffers, so no page_pool reload
> > +      * is needed. Drain NAPI before freeing the old program so
> > +      * no in-flight poll holds a stale pointer.
> > +      */
> 
> Not sure what this does. BPF programs are under RCU, they are not
> immediately freed (if that's that you mean..)
> 

It was added to stop NAPI from reading a NULL xdp_prog during a concurrent
program swap, however that issue was closed using READ_ONCE in an earlier
version. napi_synchronize() and the comment will be dropped in v6.

> > +     if (lan966x_is_pci(lan966x)) {
> > +             if (old_prog)
> > +                     napi_synchronize(&lan966x->napi);
> > +             goto out;
> > +     }

/Daniel