Historically, the felix DSA driver has installed special traps such that
PTP over L2 works with the ocelot-8021q tagging protocol; commit
0a6f17c6 ("net: dsa: tag_ocelot_8021q: add support for PTP
timestamping") has the details.

Then the ocelot switch library also gained more comprehensive support
for PTP traps through commit 96ca08c0 ("net: mscc: ocelot: set up
traps for PTP packets").

Right now, PTP over L2 works using ocelot-8021q via the traps it has set
for itself, but nothing else does. Consolidating the two code blocks
would make ocelot-8021q gain support for PTP over L4 and tc-flower
traps, and at the same time avoid some code and TCAM duplication.

The traps are similar in intent, but different in execution, so some
explanation is required. The traps set up by felix_setup_mmio_filtering()
are VCAP IS1 filters, which have a PAG that chains them to a VCAP IS2
filter, and the IS2 is where the 'trap' action resides. The traps set up
by ocelot_trap_add(), on the other hand, have a single filter, in VCAP
IS2. The reason for chaining VCAP IS1 and IS2 in Felix was to ensure
that the hardcoded traps take precedence and cannot be overridden by the
Ocelot switch library.

So in principle, the PTP traps needed for ocelot-8021q in the Felix
driver can rely on ocelot_trap_add(), but the filters need to be patched
to account for a quirk that LS1028A has: the quirk_no_xtr_irq described
in commit 0a6f17c6 ("net: dsa: tag_ocelot_8021q: add support for PTP
timestamping"). Live-patching is done by iterating through the trap list
every time we know it has been updated, and transforming a trap into a
redirect + CPU copy if ocelot-8021q is in use.

Making the DSA ocelot-8021q tagger work with the Ocelot traps means we
can eliminate the dedicated OCELOT_VCAP_IS1_TAG_8021Q_PTP_MMIO and
OCELOT_VCAP_IS2_TAG_8021Q_PTP_MMIO cookies. To minimize the patch delta,
OCELOT_VCAP_IS2_MRP_TRAP takes the place of OCELOT_VCAP_IS2_TAG_8021Q_PTP_MMIO
(the alternative would have been to left-shift all cookie numbers by 1).
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>