mlxsw: spectrum_ptp: Keep unmatched entries in a linked list

mlxsw: spectrum_ptp: Keep unmatched entries in a linked list

To identify timestamps for matching with their packets, Spectrum-1 uses a
five-tuple of (port, direction, domain number, message type, sequence ID).
If there are several clients from the same domain behind a single port
sending Delay_Req's, the only thing differentiating these packets, as far
as Spectrum-1 is concerned, is the sequence ID. Should sequence IDs between
individual clients be similar, conflicts may arise. That is not a problem
to hardware, which will simply deliver timestamps on a first comes, first
served basis.

However the driver uses a simple hash table to store the unmatched pieces.
When a new conflicting piece arrives, it pushes out the previously stored
one, which if it is a packet, is delivered without timestamp. Later on as
the corresponding timestamps arrive, the first one is mismatched to the
second packet, and the second one is never matched and eventually is GCd.

To correct this issue, instead of using a simple rhashtable, use rhltable
to keep the unmatched entries.

Previously, a found unmatched entry would always be removed from the hash
table. That is not the case anymore--an incompatible entry is left in the
hash table. Therefore removal from the hash table cannot be used to confirm
the validity of the looked-up pointer, instead the lookup would simply need
to be redone. Therefore move it inside the critical section. This
simplifies a lot of the code.

Fixes: 68ce8dcc4883 ("mlxsw: spectrum: PTP: Support SIOCGHWTSTAMP, SIOCSHWTSTAMP ioctls")
Reported-by: Alex Veber <alexve@mellanox.com>
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>