netdev - Re: [PATCH net-next 5/5] net: mscc: ocelot: support L2 multicast entries

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Message-ID: <16a2c3df-5d83-bb08-13a7-921fbd7c051e@gmail.com>
Date:   Wed, 28 Oct 2020 19:41:36 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 5/5] net: mscc: ocelot: support L2 multicast
 entries



On 10/28/2020 7:27 PM, Vladimir Oltean wrote:
> There is one main difference in mscc_ocelot between IP multicast and L2
> multicast. With IP multicast, destination ports are encoded into the
> upper bytes of the multicast MAC address. Example: to deliver the
> address 01:00:5E:11:22:33 to ports 3, 8, and 9, one would need to
> program the address of 00:03:08:11:22:33 into hardware. Whereas for L2
> multicast, the MAC table entry points to a Port Group ID (PGID), and
> that PGID contains the port mask that the packet will be forwarded to.
> As to why it is this way, no clue. My guess is that not all port
> combinations can be supported simultaneously with the limited number of
> PGIDs, and this was somehow an issue for IP multicast but not for L2
> multicast. Anyway.
> 
> Prior to this change, the raw L2 multicast code was bogus, due to the
> fact that there wasn't really any way to test it using the bridge code.
> There were 2 issues:
> - A multicast PGID was allocated for each MDB entry, but it wasn't in
>   fact programmed to hardware. It was dummy.
> - In fact we don't want to reserve a multicast PGID for every single MDB
>   entry. That would be odd because we can only have ~60 PGIDs, but
>   thousands of MDB entries. So instead, we want to reserve a multicast
>   PGID for every single port combination for multicast traffic. And
>   since we can have 2 (or more) MDB entries delivered to the same port
>   group (and therefore PGID), we need to reference-count the PGIDs.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>

I believe you have the same gfp_t comment applicable here as in patch #4.
-- 
Florian