Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted

Pull networking updates from Jakub Kicinski:
 "Core:

   - Add dedicated kmem_cache for typical/small skb->head, avoid having
     to access struct page at kfree time, and improve memory use.

   - Introduce sysctl to set default RPS configuration for new netdevs.

   - Define Netlink protocol specification format which can be used to
     describe messages used by each family and auto-generate parsers.
     Add tools for generating kernel data structures and uAPI headers.

   - Expose all net/core sysctls inside netns.

   - Remove 4s sleep in netpoll if carrier is instantly detected on
     boot.

   - Add configurable limit of MDB entries per port, and port-vlan.

   - Continue populating drop reasons throughout the stack.

   - Retire a handful of legacy Qdiscs and classifiers.

  Protocols:

   - Support IPv4 big TCP (TSO frames larger than 64kB).

   - Add IP_LOCAL_PORT_RANGE socket option, to control local port range
     on socket by socket basis.

   - Track and report in procfs number of MPTCP sockets used.

   - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path
     manager.

   - IPv6: don't check net.ipv6.route.max_size and rely on garbage
     collection to free memory (similarly to IPv4).

   - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986).

   - ICMP: add per-rate limit counters.

   - Add support for user scanning requests in ieee802154.

   - Remove static WEP support.

   - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate
     reporting.

   - WiFi 7 EHT channel puncturing support (client & AP).

  BPF:

   - Add a rbtree data structure following the "next-gen data structure"
     precedent set by recently added linked list, that is, by using
     kfunc + kptr instead of adding a new BPF map type.

   - Expose XDP hints via kfuncs with initial support for RX hash and
     timestamp metadata.

   - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to
     better support decap on GRE tunnel devices not operating in collect
     metadata.

   - Improve x86 JIT's codegen for PROBE_MEM runtime error checks.

   - Remove the need for trace_printk_lock for bpf_trace_printk and
     bpf_trace_vprintk helpers.

   - Extend libbpf's bpf_tracing.h support for tracing arguments of
     kprobes/uprobes and syscall as a special case.

   - Significantly reduce the search time for module symbols by
     livepatch and BPF.

   - Enable cpumasks to be used as kptrs, which is useful for tracing
     programs tracking which tasks end up running on which CPUs in
     different time intervals.

   - Add support for BPF trampoline on s390x and riscv64.

   - Add capability to export the XDP features supported by the NIC.

   - Add __bpf_kfunc tag for marking kernel functions as kfuncs.

   - Add cgroup.memory=nobpf kernel parameter option to disable BPF
     memory accounting for container environments.

  Netfilter:

   - Remove the CLUSTERIP target. It has been marked as obsolete for
     years, and we still have WARN splats wrt races of the out-of-band
     /proc interface installed by this target.

   - Add 'destroy' commands to nf_tables. They are identical to the
     existing 'delete' commands, but do not return an error if the
     referenced object (set, chain, rule...) did not exist.

  Driver API:

   - Improve cpumask_local_spread() locality to help NICs set the right
     IRQ affinity on AMD platforms.

   - Separate C22 and C45 MDIO bus transactions more clearly.

   - Introduce new DCB table to control DSCP rewrite on egress.

   - Support configuration of Physical Layer Collision Avoidance (PLCA)
     Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of
     shared medium Ethernet.

   - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing
     preemption of low priority frames by high priority frames.

   - Add support for controlling MACSec offload using netlink SET.

   - Rework devlink instance refcounts to allow registration and
     de-registration under the instance lock. Split the code into
     multiple files, drop some of the unnecessarily granular locks and
     factor out common parts of netlink operation handling.

   - Add TX frame aggregation parameters (for USB drivers).

   - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning
     messages with notifications for debug.

   - Allow offloading of UDP NEW connections via act_ct.

   - Add support for per action HW stats in TC.

   - Support hardware miss to TC action (continue processing in SW from
     a specific point in the action chain).

   - Warn if old Wireless Extension user space interface is used with
     modern cfg80211/mac80211 drivers. Do not support Wireless
     Extensions for Wi-Fi 7 devices at all. Everyone should switch to
     using nl80211 interface instead.

   - Improve the CAN bit timing configuration. Use extack to return
     error messages directly to user space, update the SJW handling,
     including the definition of a new default value that will benefit
     CAN-FD controllers, by increasing their oscillator tolerance.

  New hardware / drivers:

   - Ethernet:
      - nVidia BlueField-3 support (control traffic driver)
      - Ethernet support for imx93 SoCs
      - Motorcomm yt8531 gigabit Ethernet PHY
      - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA)
      - Microchip LAN8841 PHY (incl. cable diagnostics and PTP)
      - Amlogic gxl MDIO mux

   - WiFi:
      - RealTek RTL8188EU (rtl8xxxu)
      - Qualcomm Wi-Fi 7 devices (ath12k)

   - CAN:
      - Renesas R-Car V4H

  Drivers:

   - Bluetooth:
      - Set Per Platform Antenna Gain (PPAG) for Intel controllers.

   - Ethernet NICs:
      - Intel (1G, igc):
         - support TSN / Qbv / packet scheduling features of i226 model
      - Intel (100G, ice):
         - use GNSS subsystem instead of TTY
         - multi-buffer XDP support
         - extend support for GPIO pins to E823 devices
      - nVidia/Mellanox:
         - update the shared buffer configuration on PFC commands
         - implement PTP adjphase function for HW offset control
         - TC support for Geneve and GRE with VF tunnel offload
         - more efficient crypto key management method
         - multi-port eswitch support
      - Netronome/Corigine:
         - add DCB IEEE support
         - support IPsec offloading for NFP3800
      - Freescale/NXP (enetc):
         - support XDP_REDIRECT for XDP non-linear buffers
         - improve reconfig, avoid link flap and waiting for idle
         - support MAC Merge layer
      - Other NICs:
         - sfc/ef100: add basic devlink support for ef100
         - ionic: rx_push mode operation (writing descriptors via MMIO)
         - bnxt: use the auxiliary bus abstraction for RDMA
         - r8169: disable ASPM and reset bus in case of tx timeout
         - cpsw: support QSGMII mode for J721e CPSW9G
         - cpts: support pulse-per-second output
         - ngbe: add an mdio bus driver
         - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing
         - r8152: handle devices with FW with NCM support
         - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation
         - virtio-net: support multi buffer XDP
         - virtio/vsock: replace virtio_vsock_pkt with sk_buff
         - tsnep: XDP support

   - Ethernet high-speed switches:
      - nVidia/Mellanox (mlxsw):
         - add support for latency TLV (in FW control messages)
      - Microchip (sparx5):
         - separate explicit and implicit traffic forwarding rules, make
           the implicit rules always active
         - add support for egress DSCP rewrite
         - IS0 VCAP support (Ingress Classification)
         - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS
           etc.)
         - ES2 VCAP support (Egress Access Control)
         - support for Per-Stream Filtering and Policing (802.1Q,
           8.6.5.1)

   - Ethernet embedded switches:
      - Marvell (mv88e6xxx):
         - add MAB (port auth) offload support
         - enable PTP receive for mv88e6390
      - NXP (ocelot):
         - support MAC Merge layer
         - support for the the vsc7512 internal copper phys
      - Microchip:
         - lan9303: convert to PHYLINK
         - lan966x: support TC flower filter statistics
         - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x
         - lan937x: support Credit Based Shaper configuration
         - ksz9477: support Energy Efficient Ethernet
      - other:
         - qca8k: convert to regmap read/write API, use bulk operations
         - rswitch: Improve TX timestamp accuracy

   - Intel WiFi (iwlwifi):
      - EHT (Wi-Fi 7) rate reporting
      - STEP equalizer support: transfer some STEP (connection to radio
        on platforms with integrated wifi) related parameters from the
        BIOS to the firmware.

   - Qualcomm 802.11ax WiFi (ath11k):
      - IPQ5018 support
      - Fine Timing Measurement (FTM) responder role support
      - channel 177 support

   - MediaTek WiFi (mt76):
      - per-PHY LED support
      - mt7996: EHT (Wi-Fi 7) support
      - Wireless Ethernet Dispatch (WED) reset support
      - switch to using page pool allocator

   - RealTek WiFi (rtw89):
      - support new version of Bluetooth co-existance

   - Mobile:
      - rmnet: support TX aggregation"

* tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits)
  page_pool: add a comment explaining the fragment counter usage
  net: ethtool: fix __ethtool_dev_mm_supported() implementation
  ethtool: pse-pd: Fix double word in comments
  xsk: add linux/vmalloc.h to xsk.c
  sefltests: netdevsim: wait for devlink instance after netns removal
  selftest: fib_tests: Always cleanup before exit
  net/mlx5e: Align IPsec ASO result memory to be as required by hardware
  net/mlx5e: TC, Set CT miss to the specific ct action instance
  net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG
  net/mlx5: Refactor tc miss handling to a single function
  net/mlx5: Kconfig: Make tc offload depend on tc skb extension
  net/sched: flower: Support hardware miss to tc action
  net/sched: flower: Move filter handle initialization earlier
  net/sched: cls_api: Support hardware miss to tc action
  net/sched: Rename user cookie and act cookie
  sfc: fix builds without CONFIG_RTC_LIB
  sfc: clean up some inconsistent indentings
  net/mlx4_en: Introduce flexible array to silence overflow warning
  net: lan966x: Fix possible deadlock inside PTP
  net/ulp: Remove redundant ->clone() test in inet_clone_ulp().
  ...

1 files changed, 445 insertions, 0 deletions

diff --git a/Documentation/networking/dsa/sja1105.rst b/Documentation/networking/dsa/sja1105.rst
new file mode 100644
index 000000000..e0219c145
--- /dev/null
+++ b/Documentation/networking/dsa/sja1105.rst
@@ -0,0 +1,445 @@
+=========================
+NXP SJA1105 switch driver
+=========================
+
+Overview
+========
+
+The NXP SJA1105 is a family of 10 SPI-managed automotive switches:
+
+- SJA1105E: First generation, no TTEthernet
+- SJA1105T: First generation, TTEthernet
+- SJA1105P: Second generation, no TTEthernet, no SGMII
+- SJA1105Q: Second generation, TTEthernet, no SGMII
+- SJA1105R: Second generation, no TTEthernet, SGMII
+- SJA1105S: Second generation, TTEthernet, SGMII
+- SJA1110A: Third generation, TTEthernet, SGMII, integrated 100base-T1 and
+  100base-TX PHYs
+- SJA1110B: Third generation, TTEthernet, SGMII, 100base-T1, 100base-TX
+- SJA1110C: Third generation, TTEthernet, SGMII, 100base-T1, 100base-TX
+- SJA1110D: Third generation, TTEthernet, SGMII, 100base-T1
+
+Being automotive parts, their configuration interface is geared towards
+set-and-forget use, with minimal dynamic interaction at runtime. They
+require a static configuration to be composed by software and packed
+with CRC and table headers, and sent over SPI.
+
+The static configuration is composed of several configuration tables. Each
+table takes a number of entries. Some configuration tables can be (partially)
+reconfigured at runtime, some not. Some tables are mandatory, some not:
+
+============================= ================== =============================
+Table                          Mandatory          Reconfigurable
+============================= ================== =============================
+Schedule                       no                 no
+Schedule entry points          if Scheduling      no
+VL Lookup                      no                 no
+VL Policing                    if VL Lookup       no
+VL Forwarding                  if VL Lookup       no
+L2 Lookup                      no                 no
+L2 Policing                    yes                no
+VLAN Lookup                    yes                yes
+L2 Forwarding                  yes                partially (fully on P/Q/R/S)
+MAC Config                     yes                partially (fully on P/Q/R/S)
+Schedule Params                if Scheduling      no
+Schedule Entry Points Params   if Scheduling      no
+VL Forwarding Params           if VL Forwarding   no
+L2 Lookup Params               no                 partially (fully on P/Q/R/S)
+L2 Forwarding Params           yes                no
+Clock Sync Params              no                 no
+AVB Params                     no                 no
+General Params                 yes                partially
+Retagging                      no                 yes
+xMII Params                    yes                no
+SGMII                          no                 yes
+============================= ================== =============================
+
+
+Also the configuration is write-only (software cannot read it back from the
+switch except for very few exceptions).
+
+The driver creates a static configuration at probe time, and keeps it at
+all times in memory, as a shadow for the hardware state. When required to
+change a hardware setting, the static configuration is also updated.
+If that changed setting can be transmitted to the switch through the dynamic
+reconfiguration interface, it is; otherwise the switch is reset and
+reprogrammed with the updated static configuration.
+
+Switching features
+==================
+
+The driver supports the configuration of L2 forwarding rules in hardware for
+port bridging. The forwarding, broadcast and flooding domain between ports can
+be restricted through two methods: either at the L2 forwarding level (isolate
+one bridge's ports from another's) or at the VLAN port membership level
+(isolate ports within the same bridge). The final forwarding decision taken by
+the hardware is a logical AND of these two sets of rules.
+
+The hardware tags all traffic internally with a port-based VLAN (pvid), or it
+decodes the VLAN information from the 802.1Q tag. Advanced VLAN classification
+is not possible. Once attributed a VLAN tag, frames are checked against the
+port's membership rules and dropped at ingress if they don't match any VLAN.
+This behavior is available when switch ports are enslaved to a bridge with
+``vlan_filtering 1``.
+
+Normally the hardware is not configurable with respect to VLAN awareness, but
+by changing what TPID the switch searches 802.1Q tags for, the semantics of a
+bridge with ``vlan_filtering 0`` can be kept (accept all traffic, tagged or
+untagged), and therefore this mode is also supported.
+
+Segregating the switch ports in multiple bridges is supported (e.g. 2 + 2), but
+all bridges should have the same level of VLAN awareness (either both have
+``vlan_filtering`` 0, or both 1).
+
+Topology and loop detection through STP is supported.
+
+Offloads
+========
+
+Time-aware scheduling
+---------------------
+
+The switch supports a variation of the enhancements for scheduled traffic
+specified in IEEE 802.1Q-2018 (formerly 802.1Qbv). This means it can be used to
+ensure deterministic latency for priority traffic that is sent in-band with its
+gate-open event in the network schedule.
+
+This capability can be managed through the tc-taprio offload ('flags 2'). The
+difference compared to the software implementation of taprio is that the latter
+would only be able to shape traffic originated from the CPU, but not
+autonomously forwarded flows.
+
+The device has 8 traffic classes, and maps incoming frames to one of them based
+on the VLAN PCP bits (if no VLAN is present, the port-based default is used).
+As described in the previous sections, depending on the value of
+``vlan_filtering``, the EtherType recognized by the switch as being VLAN can
+either be the typical 0x8100 or a custom value used internally by the driver
+for tagging. Therefore, the switch ignores the VLAN PCP if used in standalone
+or bridge mode with ``vlan_filtering=0``, as it will not recognize the 0x8100
+EtherType. In these modes, injecting into a particular TX queue can only be
+done by the DSA net devices, which populate the PCP field of the tagging header
+on egress. Using ``vlan_filtering=1``, the behavior is the other way around:
+offloaded flows can be steered to TX queues based on the VLAN PCP, but the DSA
+net devices are no longer able to do that. To inject frames into a hardware TX
+queue with VLAN awareness active, it is necessary to create a VLAN
+sub-interface on the DSA master port, and send normal (0x8100) VLAN-tagged
+towards the switch, with the VLAN PCP bits set appropriately.
+
+Management traffic (having DMAC 01-80-C2-xx-xx-xx or 01-19-1B-xx-xx-xx) is the
+notable exception: the switch always treats it with a fixed priority and
+disregards any VLAN PCP bits even if present. The traffic class for management
+traffic has a value of 7 (highest priority) at the moment, which is not
+configurable in the driver.
+
+Below is an example of configuring a 500 us cyclic schedule on egress port
+``swp5``. The traffic class gate for management traffic (7) is open for 100 us,
+and the gates for all other traffic classes are open for 400 us::
+
+  #!/bin/bash
+
+  set -e -u -o pipefail
+
+  NSEC_PER_SEC="1000000000"
+
+  gatemask() {
+          local tc_list="$1"
+          local mask=0
+
+          for tc in ${tc_list}; do
+                  mask=$((${mask} | (1 << ${tc})))
+          done
+
+          printf "%02x" ${mask}
+  }
+
+  if ! systemctl is-active --quiet ptp4l; then
+          echo "Please start the ptp4l service"
+          exit
+  fi
+
+  now=$(phc_ctl /dev/ptp1 get | gawk '/clock time is/ { print $5; }')
+  # Phase-align the base time to the start of the next second.
+  sec=$(echo "${now}" | gawk -F. '{ print $1; }')
+  base_time="$(((${sec} + 1) * ${NSEC_PER_SEC}))"
+
+  tc qdisc add dev swp5 parent root handle 100 taprio \
+          num_tc 8 \
+          map 0 1 2 3 5 6 7 \
+          queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \
+          base-time ${base_time} \
+          sched-entry S $(gatemask 7) 100000 \
+          sched-entry S $(gatemask "0 1 2 3 4 5 6") 400000 \
+          flags 2
+
+It is possible to apply the tc-taprio offload on multiple egress ports. There
+are hardware restrictions related to the fact that no gate event may trigger
+simultaneously on two ports. The driver checks the consistency of the schedules
+against this restriction and errors out when appropriate. Schedule analysis is
+needed to avoid this, which is outside the scope of the document.
+
+Routing actions (redirect, trap, drop)
+--------------------------------------
+
+The switch is able to offload flow-based redirection of packets to a set of
+destination ports specified by the user. Internally, this is implemented by
+making use of Virtual Links, a TTEthernet concept.
+
+The driver supports 2 types of keys for Virtual Links:
+
+- VLAN-aware virtual links: these match on destination MAC address, VLAN ID and
+  VLAN PCP.
+- VLAN-unaware virtual links: these match on destination MAC address only.
+
+The VLAN awareness state of the bridge (vlan_filtering) cannot be changed while
+there are virtual link rules installed.
+
+Composing multiple actions inside the same rule is supported. When only routing
+actions are requested, the driver creates a "non-critical" virtual link. When
+the action list also contains tc-gate (more details below), the virtual link
+becomes "time-critical" (draws frame buffers from a reserved memory partition,
+etc).
+
+The 3 routing actions that are supported are "trap", "drop" and "redirect".
+
+Example 1: send frames received on swp2 with a DA of 42:be:24:9b:76:20 to the
+CPU and to swp3. This type of key (DA only) when the port's VLAN awareness
+state is off::
+
+  tc qdisc add dev swp2 clsact
+  tc filter add dev swp2 ingress flower skip_sw dst_mac 42:be:24:9b:76:20 \
+          action mirred egress redirect dev swp3 \
+          action trap
+
+Example 2: drop frames received on swp2 with a DA of 42:be:24:9b:76:20, a VID
+of 100 and a PCP of 0::
+
+  tc filter add dev swp2 ingress protocol 802.1Q flower skip_sw \
+          dst_mac 42:be:24:9b:76:20 vlan_id 100 vlan_prio 0 action drop
+
+Time-based ingress policing
+---------------------------
+
+The TTEthernet hardware abilities of the switch can be constrained to act
+similarly to the Per-Stream Filtering and Policing (PSFP) clause specified in
+IEEE 802.1Q-2018 (formerly 802.1Qci). This means it can be used to perform
+tight timing-based admission control for up to 1024 flows (identified by a
+tuple composed of destination MAC address, VLAN ID and VLAN PCP). Packets which
+are received outside their expected reception window are dropped.
+
+This capability can be managed through the offload of the tc-gate action. As
+routing actions are intrinsic to virtual links in TTEthernet (which performs
+explicit routing of time-critical traffic and does not leave that in the hands
+of the FDB, flooding etc), the tc-gate action may never appear alone when
+asking sja1105 to offload it. One (or more) redirect or trap actions must also
+follow along.
+
+Example: create a tc-taprio schedule that is phase-aligned with a tc-gate
+schedule (the clocks must be synchronized by a 1588 application stack, which is
+outside the scope of this document). No packet delivered by the sender will be
+dropped. Note that the reception window is larger than the transmission window
+(and much more so, in this example) to compensate for the packet propagation
+delay of the link (which can be determined by the 1588 application stack).
+
+Receiver (sja1105)::
+
+  tc qdisc add dev swp2 clsact
+  now=$(phc_ctl /dev/ptp1 get | awk '/clock time is/ {print $5}') && \
+          sec=$(echo $now | awk -F. '{print $1}') && \
+          base_time="$(((sec + 2) * 1000000000))" && \
+          echo "base time ${base_time}"
+  tc filter add dev swp2 ingress flower skip_sw \
+          dst_mac 42:be:24:9b:76:20 \
+          action gate base-time ${base_time} \
+          sched-entry OPEN  60000 -1 -1 \
+          sched-entry CLOSE 40000 -1 -1 \
+          action trap
+
+Sender::
+
+  now=$(phc_ctl /dev/ptp0 get | awk '/clock time is/ {print $5}') && \
+          sec=$(echo $now | awk -F. '{print $1}') && \
+          base_time="$(((sec + 2) * 1000000000))" && \
+          echo "base time ${base_time}"
+  tc qdisc add dev eno0 parent root taprio \
+          num_tc 8 \
+          map 0 1 2 3 4 5 6 7 \
+          queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \
+          base-time ${base_time} \
+          sched-entry S 01  50000 \
+          sched-entry S 00  50000 \
+          flags 2
+
+The engine used to schedule the ingress gate operations is the same that the
+one used for the tc-taprio offload. Therefore, the restrictions regarding the
+fact that no two gate actions (either tc-gate or tc-taprio gates) may fire at
+the same time (during the same 200 ns slot) still apply.
+
+To come in handy, it is possible to share time-triggered virtual links across
+more than 1 ingress port, via flow blocks. In this case, the restriction of
+firing at the same time does not apply because there is a single schedule in
+the system, that of the shared virtual link::
+
+  tc qdisc add dev swp2 ingress_block 1 clsact
+  tc qdisc add dev swp3 ingress_block 1 clsact
+  tc filter add block 1 flower skip_sw dst_mac 42:be:24:9b:76:20 \
+          action gate index 2 \
+          base-time 0 \
+          sched-entry OPEN 50000000 -1 -1 \
+          sched-entry CLOSE 50000000 -1 -1 \
+          action trap
+
+Hardware statistics for each flow are also available ("pkts" counts the number
+of dropped frames, which is a sum of frames dropped due to timing violations,
+lack of destination ports and MTU enforcement checks). Byte-level counters are
+not available.
+
+Limitations
+===========
+
+The SJA1105 switch family always performs VLAN processing. When configured as
+VLAN-unaware, frames carry a different VLAN tag internally, depending on
+whether the port is standalone or under a VLAN-unaware bridge.
+
+The virtual link keys are always fixed at {MAC DA, VLAN ID, VLAN PCP}, but the
+driver asks for the VLAN ID and VLAN PCP when the port is under a VLAN-aware
+bridge. Otherwise, it fills in the VLAN ID and PCP automatically, based on
+whether the port is standalone or in a VLAN-unaware bridge, and accepts only
+"VLAN-unaware" tc-flower keys (MAC DA).
+
+The existing tc-flower keys that are offloaded using virtual links are no
+longer operational after one of the following happens:
+
+- port was standalone and joins a bridge (VLAN-aware or VLAN-unaware)
+- port is part of a bridge whose VLAN awareness state changes
+- port was part of a bridge and becomes standalone
+- port was standalone, but another port joins a VLAN-aware bridge and this
+  changes the global VLAN awareness state of the bridge
+
+The driver cannot veto all these operations, and it cannot update/remove the
+existing tc-flower filters either. So for proper operation, the tc-flower
+filters should be installed only after the forwarding configuration of the port
+has been made, and removed by user space before making any changes to it.
+
+Device Tree bindings and board design
+=====================================
+
+This section references ``Documentation/devicetree/bindings/net/dsa/nxp,sja1105.yaml``
+and aims to showcase some potential switch caveats.
+
+RMII PHY role and out-of-band signaling
+---------------------------------------
+
+In the RMII spec, the 50 MHz clock signals are either driven by the MAC or by
+an external oscillator (but not by the PHY).
+But the spec is rather loose and devices go outside it in several ways.
+Some PHYs go against the spec and may provide an output pin where they source
+the 50 MHz clock themselves, in an attempt to be helpful.
+On the other hand, the SJA1105 is only binary configurable - when in the RMII
+MAC role it will also attempt to drive the clock signal. To prevent this from
+happening it must be put in RMII PHY role.
+But doing so has some unintended consequences.
+In the RMII spec, the PHY can transmit extra out-of-band signals via RXD[1:0].
+These are practically some extra code words (/J/ and /K/) sent prior to the
+preamble of each frame. The MAC does not have this out-of-band signaling
+mechanism defined by the RMII spec.
+So when the SJA1105 port is put in PHY role to avoid having 2 drivers on the
+clock signal, inevitably an RMII PHY-to-PHY connection is created. The SJA1105
+emulates a PHY interface fully and generates the /J/ and /K/ symbols prior to
+frame preambles, which the real PHY is not expected to understand. So the PHY
+simply encodes the extra symbols received from the SJA1105-as-PHY onto the
+100Base-Tx wire.
+On the other side of the wire, some link partners might discard these extra
+symbols, while others might choke on them and discard the entire Ethernet
+frames that follow along. This looks like packet loss with some link partners
+but not with others.
+The take-away is that in RMII mode, the SJA1105 must be let to drive the
+reference clock if connected to a PHY.
+
+RGMII fixed-link and internal delays
+------------------------------------
+
+As mentioned in the bindings document, the second generation of devices has
+tunable delay lines as part of the MAC, which can be used to establish the
+correct RGMII timing budget.
+When powered up, these can shift the Rx and Tx clocks with a phase difference
+between 73.8 and 101.7 degrees.
+The catch is that the delay lines need to lock onto a clock signal with a
+stable frequency. This means that there must be at least 2 microseconds of
+silence between the clock at the old vs at the new frequency. Otherwise the
+lock is lost and the delay lines must be reset (powered down and back up).
+In RGMII the clock frequency changes with link speed (125 MHz at 1000 Mbps, 25
+MHz at 100 Mbps and 2.5 MHz at 10 Mbps), and link speed might change during the
+AN process.
+In the situation where the switch port is connected through an RGMII fixed-link
+to a link partner whose link state life cycle is outside the control of Linux
+(such as a different SoC), then the delay lines would remain unlocked (and
+inactive) until there is manual intervention (ifdown/ifup on the switch port).
+The take-away is that in RGMII mode, the switch's internal delays are only
+reliable if the link partner never changes link speeds, or if it does, it does
+so in a way that is coordinated with the switch port (practically, both ends of
+the fixed-link are under control of the same Linux system).
+As to why would a fixed-link interface ever change link speeds: there are
+Ethernet controllers out there which come out of reset in 100 Mbps mode, and
+their driver inevitably needs to change the speed and clock frequency if it's
+required to work at gigabit.
+
+MDIO bus and PHY management
+---------------------------
+
+The SJA1105 does not have an MDIO bus and does not perform in-band AN either.
+Therefore there is no link state notification coming from the switch device.
+A board would need to hook up the PHYs connected to the switch to any other
+MDIO bus available to Linux within the system (e.g. to the DSA master's MDIO
+bus). Link state management then works by the driver manually keeping in sync
+(over SPI commands) the MAC link speed with the settings negotiated by the PHY.
+
+By comparison, the SJA1110 supports an MDIO slave access point over which its
+internal 100base-T1 PHYs can be accessed from the host. This is, however, not
+used by the driver, instead the internal 100base-T1 and 100base-TX PHYs are
+accessed through SPI commands, modeled in Linux as virtual MDIO buses.
+
+The microcontroller attached to the SJA1110 port 0 also has an MDIO controller
+operating in master mode, however the driver does not support this either,
+since the microcontroller gets disabled when the Linux driver operates.
+Discrete PHYs connected to the switch ports should have their MDIO interface
+attached to an MDIO controller from the host system and not to the switch,
+similar to SJA1105.
+
+Port compatibility matrix
+-------------------------
+
+The SJA1105 port compatibility matrix is:
+
+===== ============== ============== ==============
+Port   SJA1105E/T     SJA1105P/Q     SJA1105R/S
+===== ============== ============== ==============
+0      xMII           xMII           xMII
+1      xMII           xMII           xMII
+2      xMII           xMII           xMII
+3      xMII           xMII           xMII
+4      xMII           xMII           SGMII
+===== ============== ============== ==============
+
+
+The SJA1110 port compatibility matrix is:
+
+===== ============== ============== ============== ==============
+Port   SJA1110A       SJA1110B       SJA1110C       SJA1110D
+===== ============== ============== ============== ==============
+0      RevMII (uC)    RevMII (uC)    RevMII (uC)    RevMII (uC)
+1      100base-TX     100base-TX     100base-TX
+       or SGMII                                     SGMII
+2      xMII           xMII           xMII           xMII
+       or SGMII                                     or SGMII
+3      xMII           xMII           xMII
+       or SGMII       or SGMII                      SGMII
+       or 2500base-X  or 2500base-X                 or 2500base-X
+4      SGMII          SGMII          SGMII          SGMII
+       or 2500base-X  or 2500base-X  or 2500base-X  or 2500base-X
+5      100base-T1     100base-T1     100base-T1     100base-T1
+6      100base-T1     100base-T1     100base-T1     100base-T1
+7      100base-T1     100base-T1     100base-T1     100base-T1
+8      100base-T1     100base-T1     n/a            n/a
+9      100base-T1     100base-T1     n/a            n/a
+10     100base-T1     n/a            n/a            n/a
+===== ============== ============== ============== ==============