Re: [PATCH net-next v11 5/9] net: dsa: lan9645x: add bridge support

On Thu, 2026-08-06 at 14:38 +0000, [email protected] wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Hardware learning is not disabled when a port leaves a bridge, causing cross-port FDB pollution that breaks software bridging/routing for standalone ports.
> --
> 
> --- Patch [5]: [PATCH net-next v11 5/9] net: dsa: lan9645x: add bridge support ---
> commit f959003f0679008432479a15ff4b25747ede3826
> Author: Jens Emil Schulz Østergaard <[email protected]>
> 
>     net: dsa: lan9645x: add bridge support
> 
> Add support for hardware offloading of the bridge. We support a single
> bridge device.
> 
> > diff --git a/drivers/net/dsa/microchip/lan9645x/lan9645x_main.c b/drivers/net/dsa/microchip/lan9645x/lan9645x_main.c
> > index b253813518c20..c145d28ffbb99 100644
> > --- a/drivers/net/dsa/microchip/lan9645x/lan9645x_main.c
> > +++ b/drivers/net/dsa/microchip/lan9645x/lan9645x_main.c
> [ ... ]
> > @@ -282,6 +305,282 @@ static void lan9645x_port_phylink_get_caps(struct dsa_switch *ds, int port,
> [ ... ]
> > +static void lan9645x_port_bridge_leave(struct dsa_switch *ds, int port,
> > +                                    struct dsa_bridge bridge)
> > +{
> > +     struct lan9645x *lan9645x = ds->priv;
> > +     struct lan9645x_port *p;
> > +
> > +     p = lan9645x_to_port(lan9645x, port);
> > +
> > +     mutex_lock(&lan9645x->fwd_domain_lock);
> > +
> > +     lan9645x->bridge_mask &= ~BIT(p->chip_port);
> > +
> > +     /* Last port leaving clears bridge dev */
> > +     if (!lan9645x->bridge_mask)
> > +             lan9645x->bridge = NULL;
> > +
> > +     __lan9645x_port_set_host_flood(lan9645x);
> > +     lan9645x_update_fwd_mask(lan9645x);
> > +
> > +     mutex_unlock(&lan9645x->fwd_domain_lock);
> > +}
> 
> [Severity: High]
> Does this code need to clear p->learn_ena when a port leaves the bridge?
> 
> When a port is removed from the hardware bridge, its learning state incorrectly
> remains enabled.
> 

It does not remain enabled. The DSA core resets the bridge port flags on
bridge leave, learning included, and it does so before it puts the port
back into BR_STATE_FORWARDING.

dsa_port_bridge_leave() ends in dsa_port_switchdev_unsync_attrs(), which
calls dsa_port_clear_brport_flags() first and dsa_port_set_state_now(dp,
BR_STATE_FORWARDING, true) second. BR_LEARNING is in that helpers mask
but not in its val, so the driver is called with mask = BR_LEARNING,
val = 0, and lan9645x_port_set_learning() clears p->learn_ena and writes
ANA_PORT_CFG.LEARN_ENA = 0 immediately.

So by the time lan9645x_port_bridge_stp_state_set() evaluates

      (state == BR_STATE_LEARNING || state == BR_STATE_FORWARDING) &&
      p->learn_ena

p->learn_ena is already false and hardware learning stays off. Clearing
it in lan9645x_port_bridge_leave() would be redundant.



>  If this port and another port are later added to a software
> bridge (for example, if the hardware only supports one offloaded bridge), the
> DSA core transitions the standalone port to BR_STATE_FORWARDING.
> 
> Because p->learn_ena was not cleared during bridge leave, the call to
> lan9645x_port_bridge_stp_state_set() will incorrectly re-enable hardware
> learning for the standalone port:
> 
>         learn_ena = (state == BR_STATE_LEARNING ||
>                      state == BR_STATE_FORWARDING) && p->learn_ena;
> 
>         lan_rmw(ANA_PORT_CFG_LEARN_ENA_SET(learn_ena), ...
> 
> This causes the port to learn MAC addresses into the shared HOST_PVID FDB used
> by standalone ports. When the other software-bridged port (which expects to
> send unknown unicast traffic to the CPU) receives traffic for a MAC dynamically
> learned by this port, the hardware resolves the destination.
> 
> However, since PGID_SRC for standalone ports is 0, the packet is silently
> dropped in hardware instead of being forwarded to the CPU, breaking network
> connectivity for the fallback software bridge.
> 
> --
> Sashiko AI review · https://sashiko.dev/#/patchset/20260805-dsa_lan9645x_switch_driver_base-v11-0-007ebc983a0a@microchip.com?part=5