Hi Sasha,
On Mon, Aug 10, 2020 at 03:09:31PM -0400, Sasha Levin wrote:
From: Vladimir Oltean vladimir.oltean@nxp.com
[ Upstream commit 0897ecf7532577bda3dbcb043ce046a96948889d ]
The ocelot hardware designers have made some hacks to support multicast IPv4 and IPv6 addresses. Normally, the MAC table matches on MAC addresses and the destination ports are selected through the DEST_IDX field of the respective MAC table entry. The DEST_IDX points to a Port Group ID (PGID) which contains the bit mask of ports that frames should be forwarded to. But there aren't a lot of PGIDs (only 80 or so) and there are clearly many more IP multicast addresses than that, so it doesn't scale to use this PGID mechanism, so something else was done. Since the first portion of the MAC address is known, the hack they did was to use a single PGID for _flooding_ unknown IPv4 multicast (PGID_MCIPV4 == 62), but for known IP multicast, embed the destination ports into the first 3 bytes of the MAC address recorded in the MAC table.
The VSC7514 datasheet explains it like this:
3.9.1.5 IPv4 Multicast Entries MAC table entries with the ENTRY_TYPE = 2 settings are interpreted as IPv4 multicast entries. IPv4 multicasts entries match IPv4 frames, which are classified to the specified VID, and which have DMAC = 0x01005Exxxxxx, where xxxxxx is the lower 24 bits of the MAC address in the entry. Instead of a lookup in the destination mask table (PGID), the destination set is programmed as part of the entry MAC address. This is shown in the following table. Table 78: IPv4 Multicast Destination Mask Destination Ports Record Bit Field --------------------------------------------- Ports 10-0 MAC[34-24] Example: All IPv4 multicast frames in VLAN 12 with MAC 01005E112233 are to be forwarded to ports 3, 8, and 9. This is done by inserting the following entry in the MAC table entry: VALID = 1 VID = 12 MAC = 0x000308112233 ENTRY_TYPE = 2 DEST_IDX = 0But this procedure is not at all what's going on in the driver. In fact, the code that embeds the ports into the MAC address looks like it hasn't actually been tested. This patch applies the procedure described in the datasheet.
Since there are many other fixes to be made around multicast forwarding until it works properly, there is no real reason for this patch to be backported to stable trees, or considered a real fix of something that should have worked.
Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org
Could you please drop this patch from the 'stable' queues for 5.7 and 5.8? I haven't tested it on older kernels and without the other patches sent in that series. I would like to avoid unexpected regressions if possible.
Thanks, -Vladimir