[ethernet/broadcom/bgmac]: Implement software multicast filter clear

[ethernet/broadcom/bgmac]: Implement software multicast filter clear

[Ujwal Kundur]

Hi,
   I'm trying to work on a few TODOs in the
drivers/net/ethernet/broadcom/bgmac.c driver code and came across the
"Clear software multicast filter list" item.
   I tried comparing the multicast filter implementation of the
sb1250-mac.c driver for inspiration but realized that most of the code
for bgmac has been written by reverse-engineering the specs:
   hhttps://bcm-v4.sipsolutions.net/Specification/

   I'd like to try my hand at this if there are documents/guides
around this topic or if there's a canonical source for the binary that
I can try reverse engineering. Please let me know if you have any
leads/advice.

   Apologies if this is misdirected, I've just started to get into
Linux kernel development / networking stack.

Thanks,
            Ujwal Kundur

Re: [ethernet/broadcom/bgmac]: Implement software multicast filter clear

[Florian Fainelli]

Howdy,

On 4/13/25 00:25, Ujwal Kundur wrote:
> Hi,
>     I'm trying to work on a few TODOs in the
> drivers/net/ethernet/broadcom/bgmac.c driver code and came across the
> "Clear software multicast filter list" item.
>     I tried comparing the multicast filter implementation of the
> sb1250-mac.c driver for inspiration but realized that most of the code
> for bgmac has been written by reverse-engineering the specs:
>     hhttps://bcm-v4.sipsolutions.net/Specification/
> 
>     I'd like to try my hand at this if there are documents/guides
> around this topic or if there's a canonical source for the binary that
> I can try reverse engineering. Please let me know if you have any
> leads/advice.

Given that these controllers are always interfaced with either an 
integrated or an external Ethernet switch chip, the design was done 
assuming that the switch will be operated in managed mode and multicast 
filtering will be done on the switch side.

It's been a while since I looked at that part of the DSA and bridge 
stack, but we should be pretty close to having that capability nowadays.
-- 
Florian

Re: [ethernet/broadcom/bgmac]: Implement software multicast filter clear

[Ujwal Kundur]

Hello!

> Given that these controllers are always interfaced with either an
> integrated or an external Ethernet switch chip, the design was done
> assuming that the switch will be operated in managed mode and multicast
> filtering will be done on the switch side.

Thanks for the info, I wasn't aware of this. I infer that this is
relevant from your message and the codebase:
https://docs.kernel.org/networking/dsa/dsa.html

If I understand correctly, this TODO is basically a no-op because DSA
already implements `dsa_mc_add` / `dsa_mc_del`
for handling multicast addresses on the switch side.

I'll hop over to `bcnxt` as I see some TODOs there, or find something
easier to work with for starters. Thanks again.

--- Ujwal.