linux/net/dsa
Vladimir Oltean dc452a471d net: dsa: introduce tagger-owned storage for private and shared data
Ansuel is working on register access over Ethernet for the qca8k switch
family. This requires the qca8k tagging protocol driver to receive
frames which aren't intended for the network stack, but instead for the
qca8k switch driver itself.

The dp->priv is currently the prevailing method for passing data back
and forth between the tagging protocol driver and the switch driver.
However, this method is riddled with caveats.

The DSA design allows in principle for any switch driver to return any
protocol it desires in ->get_tag_protocol(). The dsa_loop driver can be
modified to do just that. But in the current design, the memory behind
dp->priv has to be allocated by the switch driver, so if the tagging
protocol is paired to an unexpected switch driver, we may end up in NULL
pointer dereferences inside the kernel, or worse (a switch driver may
allocate dp->priv according to the expectations of a different tagger).

The latter possibility is even more plausible considering that DSA
switches can dynamically change tagging protocols in certain cases
(dsa <-> edsa, ocelot <-> ocelot-8021q), and the current design lends
itself to mistakes that are all too easy to make.

This patch proposes that the tagging protocol driver should manage its
own memory, instead of relying on the switch driver to do so.
After analyzing the different in-tree needs, it can be observed that the
required tagger storage is per switch, therefore a ds->tagger_data
pointer is introduced. In principle, per-port storage could also be
introduced, although there is no need for it at the moment. Future
changes will replace the current usage of dp->priv with ds->tagger_data.

We define a "binding" event between the DSA switch tree and the tagging
protocol. During this binding event, the tagging protocol's ->connect()
method is called first, and this may allocate some memory for each
switch of the tree. Then a cross-chip notifier is emitted for the
switches within that tree, and they are given the opportunity to fix up
the tagger's memory (for example, they might set up some function
pointers that represent virtual methods for consuming packets).
Because the memory is owned by the tagger, there exists a ->disconnect()
method for the tagger (which is the place to free the resources), but
there doesn't exist a ->disconnect() method for the switch driver.
This is part of the design. The switch driver should make minimal use of
the public part of the tagger data, and only after type-checking it
using the supplied "proto" argument.

In the code there are in fact two binding events, one is the initial
event in dsa_switch_setup_tag_protocol(). At this stage, the cross chip
notifier chains aren't initialized, so we call each switch's connect()
method by hand. Then there is dsa_tree_bind_tag_proto() during
dsa_tree_change_tag_proto(), and here we have an old protocol and a new
one. We first connect to the new one before disconnecting from the old
one, to simplify error handling a bit and to ensure we remain in a valid
state at all times.

Co-developed-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2021-12-12 12:51:33 +00:00
..
dsa2.c net: dsa: introduce tagger-owned storage for private and shared data 2021-12-12 12:51:33 +00:00
dsa_priv.h net: dsa: introduce tagger-owned storage for private and shared data 2021-12-12 12:51:33 +00:00
dsa.c devlink: Simplify devlink resources unregister call 2021-11-30 12:23:32 +00:00
Kconfig net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag 2021-10-18 14:02:56 +01:00
Makefile net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag 2021-10-18 14:02:56 +01:00
master.c dev_ioctl: split out ndo_eth_ioctl 2021-07-27 20:11:45 +01:00
port.c net: dsa: mark DSA phylink as legacy_pre_march2020 2021-12-09 11:21:03 -08:00
slave.c net: dsa: keep the bridge_dev and bridge_num as part of the same structure 2021-12-08 14:31:16 -08:00
switch.c net: dsa: introduce tagger-owned storage for private and shared data 2021-12-12 12:51:33 +00:00
tag_8021q.c net: dsa: keep the bridge_dev and bridge_num as part of the same structure 2021-12-08 14:31:16 -08:00
tag_ar9331.c net: dsa: remove the struct packet_type argument from dsa_device_ops::rcv() 2021-08-02 15:13:15 +01:00
tag_brcm.c net: dsa: create a helper for locating EtherType DSA headers on RX 2021-08-11 14:44:58 +01:00
tag_dsa.c net: dsa: hide dp->bridge_dev and dp->bridge_num in the core behind helpers 2021-12-08 14:31:15 -08:00
tag_gswip.c net: dsa: remove the struct packet_type argument from dsa_device_ops::rcv() 2021-08-02 15:13:15 +01:00
tag_hellcreek.c net: dsa: remove the struct packet_type argument from dsa_device_ops::rcv() 2021-08-02 15:13:15 +01:00
tag_ksz.c net/dsa/tag_ksz.c: remove superfluous headers 2021-09-29 11:38:21 +01:00
tag_lan9303.c net: dsa: create a helper for locating EtherType DSA headers on TX 2021-08-11 14:44:58 +01:00
tag_mtk.c net: dsa: create a helper for locating EtherType DSA headers on TX 2021-08-11 14:44:58 +01:00
tag_ocelot_8021q.c net: dsa: tag_8021q: make dsa_8021q_{rx,tx}_vid take dp as argument 2021-10-21 12:44:07 +01:00
tag_ocelot.c net: dsa: hide dp->bridge_dev and dp->bridge_num in the core behind helpers 2021-12-08 14:31:15 -08:00
tag_qca.c net: dsa: create a helper for locating EtherType DSA headers on TX 2021-08-11 14:44:58 +01:00
tag_rtl4_a.c net: dsa: tag_rtl4_a: Drop bit 9 from egress frames 2021-09-14 19:34:03 -07:00
tag_rtl8_4.c net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag 2021-10-18 14:02:56 +01:00
tag_sja1105.c net: dsa: hide dp->bridge_dev and dp->bridge_num in the core behind helpers 2021-12-08 14:31:15 -08:00
tag_trailer.c net: dsa: remove the struct packet_type argument from dsa_device_ops::rcv() 2021-08-02 15:13:15 +01:00
tag_xrs700x.c net: dsa: remove the struct packet_type argument from dsa_device_ops::rcv() 2021-08-02 15:13:15 +01:00