Re: [PATCH net v2] net: dsa: b53: Enable IGMP and MLD control packet CPU copies

[Florian Fainelli]

On 10/28/26 03:30, Jonas Gorski wrote:
> On Wed, Oct 28, 2026 at 1:10 AM Florian Fainelli
> <florian.fainelli@xxxxxxxxxxxx> wrote:
> > IGMPv2 reports and MLDv1 reports are addressed to the multicast group
> > itself. Once the first listener is installed in the ARL table, subsequent
> > reports can follow that entry without reaching the CPU. The bridge then
> > fails to learn additional listeners, although static MDB forwarding works.
> >
> > Enable the high-level protocol classifiers so that IGMP and MLD control
> > packets are copied to the CPU independently of the multicast ARL lookup.
> > Retain normal L2 forwarding by clearing the CPU-only forwarding modes,
> > and preserve unrelated protocol-control fields.
> >
> > Handle the BCM5395's 16-bit register and different classifier fields
> > separately from the 32-bit layout on the BCM531xx, BCM5301x and newer
> > integrated RoboSwitch families, including BCM7445, BCM7278 and BCM4908.
> > Export the helper and call it from bcm_sf2_sw_setup() as well, since SF2
> > uses its own setup operation instead of b53_setup(). This also restores
> > the classifiers after the switch reset on resume. Leave older devices
> > with different IGMP controls untouched, and propagate register access
> > failures during setup.
> >
> > The SF2 setup integration and BCM4908 chip gate were updated with
> > assistance from OpenAI Codex in response to review feedback.
> >
> > Fixes: 5d65b64a3d97 ("net: dsa: b53: Add support for MDB")
> > Signed-off-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
> > ---
> > Changes in v2:
> >
> > - export the helper and call it from bcm_sf2.c as well as spotted by
> >    Sashiko
> >
> >   drivers/net/dsa/b53/b53_common.c | 52 ++++++++++++++++++++++++++++++++
> >   drivers/net/dsa/b53/b53_priv.h   |  1 +
> >   drivers/net/dsa/b53/b53_regs.h   | 17 +++++++++++
> >   drivers/net/dsa/bcm_sf2.c        |  5 +++
> >   4 files changed, 75 insertions(+)
> >
> > diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
> > index 0880310c9ce3..51784432d266 100644
> > --- a/drivers/net/dsa/b53/b53_common.c
> > +++ b/drivers/net/dsa/b53/b53_common.c
> > @@ -836,6 +836,54 @@ void b53_brcm_hdr_setup(struct dsa_switch *ds, int port)
> >   }
> >   EXPORT_SYMBOL(b53_brcm_hdr_setup);
> >
> > +int b53_enable_mcast_snooping(struct b53_device *dev)
> > +{
> > +       u32 val;
> > +       u16 val16;
> > +       int ret;
>
> I'm surprised to be the first to say that, but ... reverse christmas
> tree? Or is this not a thing anymore?

Indeed.

> > +
> > +       /* BCM5395 has a narrower register and a single IGMP classifier.
> > +        * Its ICMPv6 classifier also covers MLD.
> > +        */
> > +       if (dev->chip_id == BCM5395_DEVICE_ID) {
> > +               ret = b53_read16(dev, B53_MGMT_PAGE, B53_HL_PRTC_CTRL, &val16);
> > +               if (ret)
> > +                       return ret;
> > +
> > +               val16 |= HL_PRTC_IGMP_IP_EN_5395 | HL_PRTC_ICMPV6_EN;
> > +               val16 &= ~(HL_PRTC_IGMP_FWD_MODE_5395 |
> > +                          HL_PRTC_ICMPV6_FWD_MODE);
> > +
> > +               return b53_write16(dev, B53_MGMT_PAGE, B53_HL_PRTC_CTRL,
> > +                                  val16);
> > +       }
> > +
> > +       /* Older switches use different IGMP controls, not HL_PRTC_CTRL. */
> > +       if (!is531x5(dev) && !is5301x(dev) && !is58xx(dev) &&
> > +           dev->chip_id != BCM4908_DEVICE_ID)
> > +               return 0;
>
> I would move this to top, and probably check for those that don't have
> it. Basically go from oldest to newest generation code wise.

Sounds good, I will actually add a second patch that enables IGMP/MLD 
snooping for the older generations as well.

> > +
> > +       ret = b53_read32(dev, B53_MGMT_PAGE, B53_HL_PRTC_CTRL, &val);
> > +       if (ret)
> > +               return ret;
> > +
> > +       /* IGMPv2 and MLDv1 reports use the group's destination MAC. Once
> > +        * the first listener is offloaded, ordinary multicast forwarding
> > +        * can keep subsequent reports from reaching the bridge CPU.
> > +        * Copy control traffic to the CPU independently of the ARL lookup,
> > +        * retaining L2 forwarding rather than selecting CPU-only traps.
> > +        */
>
> Should this comment be also in the 5395 case? Feels like it would apply to both.

Yes, this comment has been moved to the top now since it applies to both 
cases.

> > +       val |= HL_PRTC_IGMP_RPTLVE_EN | HL_PRTC_IGMP_QRY_EN |
> > +              HL_PRTC_IGMP_UKN_EN | HL_PRTC_MLD_RPTDONE_EN |
> > +              HL_PRTC_MLD_QRY_EN;
>
> I would also break out the "Copy control" part and move it here, to
> make it more obvious that these bits control this, and clearer that 0
> means copy to CPU instead of trap to CPU.

Yes, done as well, thanks!
--
Florian