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authorLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
committerLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
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treecc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/i2c/i2c-topology.rst
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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(). ...
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+================================
+I2C muxes and complex topologies
+================================
+
+There are a couple of reasons for building more complex I2C topologies
+than a straight-forward I2C bus with one adapter and one or more devices.
+
+Some example use cases are:
+
+1. A mux may be needed on the bus to prevent address collisions.
+
+2. The bus may be accessible from some external bus master, and arbitration
+ may be needed to determine if it is ok to access the bus.
+
+3. A device (particularly RF tuners) may want to avoid the digital noise
+ from the I2C bus, at least most of the time, and sits behind a gate
+ that has to be operated before the device can be accessed.
+
+Several types of hardware components such as I2C muxes, I2C gates and I2C
+arbitrators allow to handle such needs.
+
+These components are represented as I2C adapter trees by Linux, where
+each adapter has a parent adapter (except the root adapter) and zero or
+more child adapters. The root adapter is the actual adapter that issues
+I2C transfers, and all adapters with a parent are part of an "i2c-mux"
+object (quoted, since it can also be an arbitrator or a gate).
+
+Depending of the particular mux driver, something happens when there is
+an I2C transfer on one of its child adapters. The mux driver can
+obviously operate a mux, but it can also do arbitration with an external
+bus master or open a gate. The mux driver has two operations for this,
+select and deselect. select is called before the transfer and (the
+optional) deselect is called after the transfer.
+
+
+Locking
+=======
+
+There are two variants of locking available to I2C muxes, they can be
+mux-locked or parent-locked muxes.
+
+
+Mux-locked muxes
+----------------
+
+Mux-locked muxes does not lock the entire parent adapter during the
+full select-transfer-deselect transaction, only the muxes on the parent
+adapter are locked. Mux-locked muxes are mostly interesting if the
+select and/or deselect operations must use I2C transfers to complete
+their tasks. Since the parent adapter is not fully locked during the
+full transaction, unrelated I2C transfers may interleave the different
+stages of the transaction. This has the benefit that the mux driver
+may be easier and cleaner to implement, but it has some caveats.
+
+Mux-locked Example
+~~~~~~~~~~~~~~~~~~
+
+::
+
+ .----------. .--------.
+ .--------. | mux- |-----| dev D1 |
+ | root |--+--| locked | '--------'
+ '--------' | | mux M1 |--. .--------.
+ | '----------' '--| dev D2 |
+ | .--------. '--------'
+ '--| dev D3 |
+ '--------'
+
+When there is an access to D1, this happens:
+
+ 1. Someone issues an I2C transfer to D1.
+ 2. M1 locks muxes on its parent (the root adapter in this case).
+ 3. M1 calls ->select to ready the mux.
+ 4. M1 (presumably) does some I2C transfers as part of its select.
+ These transfers are normal I2C transfers that locks the parent
+ adapter.
+ 5. M1 feeds the I2C transfer from step 1 to its parent adapter as a
+ normal I2C transfer that locks the parent adapter.
+ 6. M1 calls ->deselect, if it has one.
+ 7. Same rules as in step 4, but for ->deselect.
+ 8. M1 unlocks muxes on its parent.
+
+This means that accesses to D2 are lockout out for the full duration
+of the entire operation. But accesses to D3 are possibly interleaved
+at any point.
+
+Mux-locked caveats
+~~~~~~~~~~~~~~~~~~
+
+When using a mux-locked mux, be aware of the following restrictions:
+
+[ML1]
+ If you build a topology with a mux-locked mux being the parent
+ of a parent-locked mux, this might break the expectation from the
+ parent-locked mux that the root adapter is locked during the
+ transaction.
+
+[ML2]
+ It is not safe to build arbitrary topologies with two (or more)
+ mux-locked muxes that are not siblings, when there are address
+ collisions between the devices on the child adapters of these
+ non-sibling muxes.
+
+ I.e. the select-transfer-deselect transaction targeting e.g. device
+ address 0x42 behind mux-one may be interleaved with a similar
+ operation targeting device address 0x42 behind mux-two. The
+ intent with such a topology would in this hypothetical example
+ be that mux-one and mux-two should not be selected simultaneously,
+ but mux-locked muxes do not guarantee that in all topologies.
+
+[ML3]
+ A mux-locked mux cannot be used by a driver for auto-closing
+ gates/muxes, i.e. something that closes automatically after a given
+ number (one, in most cases) of I2C transfers. Unrelated I2C transfers
+ may creep in and close prematurely.
+
+[ML4]
+ If any non-I2C operation in the mux driver changes the I2C mux state,
+ the driver has to lock the root adapter during that operation.
+ Otherwise garbage may appear on the bus as seen from devices
+ behind the mux, when an unrelated I2C transfer is in flight during
+ the non-I2C mux-changing operation.
+
+
+Parent-locked muxes
+-------------------
+
+Parent-locked muxes lock the parent adapter during the full select-
+transfer-deselect transaction. The implication is that the mux driver
+has to ensure that any and all I2C transfers through that parent
+adapter during the transaction are unlocked I2C transfers (using e.g.
+__i2c_transfer), or a deadlock will follow.
+
+Parent-locked Example
+~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ .----------. .--------.
+ .--------. | parent- |-----| dev D1 |
+ | root |--+--| locked | '--------'
+ '--------' | | mux M1 |--. .--------.
+ | '----------' '--| dev D2 |
+ | .--------. '--------'
+ '--| dev D3 |
+ '--------'
+
+When there is an access to D1, this happens:
+
+ 1. Someone issues an I2C transfer to D1.
+ 2. M1 locks muxes on its parent (the root adapter in this case).
+ 3. M1 locks its parent adapter.
+ 4. M1 calls ->select to ready the mux.
+ 5. If M1 does any I2C transfers (on this root adapter) as part of
+ its select, those transfers must be unlocked I2C transfers so
+ that they do not deadlock the root adapter.
+ 6. M1 feeds the I2C transfer from step 1 to the root adapter as an
+ unlocked I2C transfer, so that it does not deadlock the parent
+ adapter.
+ 7. M1 calls ->deselect, if it has one.
+ 8. Same rules as in step 5, but for ->deselect.
+ 9. M1 unlocks its parent adapter.
+ 10. M1 unlocks muxes on its parent.
+
+This means that accesses to both D2 and D3 are locked out for the full
+duration of the entire operation.
+
+Parent-locked Caveats
+~~~~~~~~~~~~~~~~~~~~~
+
+When using a parent-locked mux, be aware of the following restrictions:
+
+[PL1]
+ If you build a topology with a parent-locked mux being the child
+ of another mux, this might break a possible assumption from the
+ child mux that the root adapter is unused between its select op
+ and the actual transfer (e.g. if the child mux is auto-closing
+ and the parent mux issues I2C transfers as part of its select).
+ This is especially the case if the parent mux is mux-locked, but
+ it may also happen if the parent mux is parent-locked.
+
+[PL2]
+ If select/deselect calls out to other subsystems such as gpio,
+ pinctrl, regmap or iio, it is essential that any I2C transfers
+ caused by these subsystems are unlocked. This can be convoluted to
+ accomplish, maybe even impossible if an acceptably clean solution
+ is sought.
+
+
+Complex Examples
+================
+
+Parent-locked mux as parent of parent-locked mux
+------------------------------------------------
+
+This is a useful topology, but it can be bad::
+
+ .----------. .----------. .--------.
+ .--------. | parent- |-----| parent- |-----| dev D1 |
+ | root |--+--| locked | | locked | '--------'
+ '--------' | | mux M1 |--. | mux M2 |--. .--------.
+ | '----------' | '----------' '--| dev D2 |
+ | .--------. | .--------. '--------'
+ '--| dev D4 | '--| dev D3 |
+ '--------' '--------'
+
+When any device is accessed, all other devices are locked out for
+the full duration of the operation (both muxes lock their parent,
+and specifically when M2 requests its parent to lock, M1 passes
+the buck to the root adapter).
+
+This topology is bad if M2 is an auto-closing mux and M1->select
+issues any unlocked I2C transfers on the root adapter that may leak
+through and be seen by the M2 adapter, thus closing M2 prematurely.
+
+
+Mux-locked mux as parent of mux-locked mux
+------------------------------------------
+
+This is a good topology::
+
+ .----------. .----------. .--------.
+ .--------. | mux- |-----| mux- |-----| dev D1 |
+ | root |--+--| locked | | locked | '--------'
+ '--------' | | mux M1 |--. | mux M2 |--. .--------.
+ | '----------' | '----------' '--| dev D2 |
+ | .--------. | .--------. '--------'
+ '--| dev D4 | '--| dev D3 |
+ '--------' '--------'
+
+When device D1 is accessed, accesses to D2 are locked out for the
+full duration of the operation (muxes on the top child adapter of M1
+are locked). But accesses to D3 and D4 are possibly interleaved at
+any point.
+
+Accesses to D3 locks out D1 and D2, but accesses to D4 are still possibly
+interleaved.
+
+
+Mux-locked mux as parent of parent-locked mux
+---------------------------------------------
+
+This is probably a bad topology::
+
+ .----------. .----------. .--------.
+ .--------. | mux- |-----| parent- |-----| dev D1 |
+ | root |--+--| locked | | locked | '--------'
+ '--------' | | mux M1 |--. | mux M2 |--. .--------.
+ | '----------' | '----------' '--| dev D2 |
+ | .--------. | .--------. '--------'
+ '--| dev D4 | '--| dev D3 |
+ '--------' '--------'
+
+When device D1 is accessed, accesses to D2 and D3 are locked out
+for the full duration of the operation (M1 locks child muxes on the
+root adapter). But accesses to D4 are possibly interleaved at any
+point.
+
+This kind of topology is generally not suitable and should probably
+be avoided. The reason is that M2 probably assumes that there will
+be no I2C transfers during its calls to ->select and ->deselect, and
+if there are, any such transfers might appear on the slave side of M2
+as partial I2C transfers, i.e. garbage or worse. This might cause
+device lockups and/or other problems.
+
+The topology is especially troublesome if M2 is an auto-closing
+mux. In that case, any interleaved accesses to D4 might close M2
+prematurely, as might any I2C transfers part of M1->select.
+
+But if M2 is not making the above stated assumption, and if M2 is not
+auto-closing, the topology is fine.
+
+
+Parent-locked mux as parent of mux-locked mux
+---------------------------------------------
+
+This is a good topology::
+
+ .----------. .----------. .--------.
+ .--------. | parent- |-----| mux- |-----| dev D1 |
+ | root |--+--| locked | | locked | '--------'
+ '--------' | | mux M1 |--. | mux M2 |--. .--------.
+ | '----------' | '----------' '--| dev D2 |
+ | .--------. | .--------. '--------'
+ '--| dev D4 | '--| dev D3 |
+ '--------' '--------'
+
+When D1 is accessed, accesses to D2 are locked out for the full
+duration of the operation (muxes on the top child adapter of M1
+are locked). Accesses to D3 and D4 are possibly interleaved at
+any point, just as is expected for mux-locked muxes.
+
+When D3 or D4 are accessed, everything else is locked out. For D3
+accesses, M1 locks the root adapter. For D4 accesses, the root
+adapter is locked directly.
+
+
+Two mux-locked sibling muxes
+----------------------------
+
+This is a good topology::
+
+ .--------.
+ .----------. .--| dev D1 |
+ | mux- |--' '--------'
+ .--| locked | .--------.
+ | | mux M1 |-----| dev D2 |
+ | '----------' '--------'
+ | .----------. .--------.
+ .--------. | | mux- |-----| dev D3 |
+ | root |--+--| locked | '--------'
+ '--------' | | mux M2 |--. .--------.
+ | '----------' '--| dev D4 |
+ | .--------. '--------'
+ '--| dev D5 |
+ '--------'
+
+When D1 is accessed, accesses to D2, D3 and D4 are locked out. But
+accesses to D5 may be interleaved at any time.
+
+
+Two parent-locked sibling muxes
+-------------------------------
+
+This is a good topology::
+
+ .--------.
+ .----------. .--| dev D1 |
+ | parent- |--' '--------'
+ .--| locked | .--------.
+ | | mux M1 |-----| dev D2 |
+ | '----------' '--------'
+ | .----------. .--------.
+ .--------. | | parent- |-----| dev D3 |
+ | root |--+--| locked | '--------'
+ '--------' | | mux M2 |--. .--------.
+ | '----------' '--| dev D4 |
+ | .--------. '--------'
+ '--| dev D5 |
+ '--------'
+
+When any device is accessed, accesses to all other devices are locked
+out.
+
+
+Mux-locked and parent-locked sibling muxes
+------------------------------------------
+
+This is a good topology::
+
+ .--------.
+ .----------. .--| dev D1 |
+ | mux- |--' '--------'
+ .--| locked | .--------.
+ | | mux M1 |-----| dev D2 |
+ | '----------' '--------'
+ | .----------. .--------.
+ .--------. | | parent- |-----| dev D3 |
+ | root |--+--| locked | '--------'
+ '--------' | | mux M2 |--. .--------.
+ | '----------' '--| dev D4 |
+ | .--------. '--------'
+ '--| dev D5 |
+ '--------'
+
+When D1 or D2 are accessed, accesses to D3 and D4 are locked out while
+accesses to D5 may interleave. When D3 or D4 are accessed, accesses to
+all other devices are locked out.
+
+
+Mux type of existing device drivers
+===================================
+
+Whether a device is mux-locked or parent-locked depends on its
+implementation. The following list was correct at the time of writing:
+
+In drivers/i2c/muxes/:
+
+====================== =============================================
+i2c-arb-gpio-challenge Parent-locked
+i2c-mux-gpio Normally parent-locked, mux-locked iff
+ all involved gpio pins are controlled by the
+ same I2C root adapter that they mux.
+i2c-mux-gpmux Normally parent-locked, mux-locked iff
+ specified in device-tree.
+i2c-mux-ltc4306 Mux-locked
+i2c-mux-mlxcpld Parent-locked
+i2c-mux-pca9541 Parent-locked
+i2c-mux-pca954x Parent-locked
+i2c-mux-pinctrl Normally parent-locked, mux-locked iff
+ all involved pinctrl devices are controlled
+ by the same I2C root adapter that they mux.
+i2c-mux-reg Parent-locked
+====================== =============================================
+
+In drivers/iio/:
+
+====================== =============================================
+gyro/mpu3050 Mux-locked
+imu/inv_mpu6050/ Mux-locked
+====================== =============================================
+
+In drivers/media/:
+
+======================= =============================================
+dvb-frontends/lgdt3306a Mux-locked
+dvb-frontends/m88ds3103 Parent-locked
+dvb-frontends/rtl2830 Parent-locked
+dvb-frontends/rtl2832 Mux-locked
+dvb-frontends/si2168 Mux-locked
+usb/cx231xx/ Parent-locked
+======================= =============================================