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author | 2023-02-21 18:24:12 -0800 | |
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committer | 2023-02-21 18:24:12 -0800 | |
commit | 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch) | |
tree | cc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/driver-api/pwm.rst | |
download | linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.tar.gz linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.zip |
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().
...
Diffstat (limited to 'Documentation/driver-api/pwm.rst')
-rw-r--r-- | Documentation/driver-api/pwm.rst | 179 |
1 files changed, 179 insertions, 0 deletions
diff --git a/Documentation/driver-api/pwm.rst b/Documentation/driver-api/pwm.rst new file mode 100644 index 000000000..8c71a2055 --- /dev/null +++ b/Documentation/driver-api/pwm.rst @@ -0,0 +1,179 @@ +====================================== +Pulse Width Modulation (PWM) interface +====================================== + +This provides an overview about the Linux PWM interface + +PWMs are commonly used for controlling LEDs, fans or vibrators in +cell phones. PWMs with a fixed purpose have no need implementing +the Linux PWM API (although they could). However, PWMs are often +found as discrete devices on SoCs which have no fixed purpose. It's +up to the board designer to connect them to LEDs or fans. To provide +this kind of flexibility the generic PWM API exists. + +Identifying PWMs +---------------- + +Users of the legacy PWM API use unique IDs to refer to PWM devices. + +Instead of referring to a PWM device via its unique ID, board setup code +should instead register a static mapping that can be used to match PWM +consumers to providers, as given in the following example:: + + static struct pwm_lookup board_pwm_lookup[] = { + PWM_LOOKUP("tegra-pwm", 0, "pwm-backlight", NULL, + 50000, PWM_POLARITY_NORMAL), + }; + + static void __init board_init(void) + { + ... + pwm_add_table(board_pwm_lookup, ARRAY_SIZE(board_pwm_lookup)); + ... + } + +Using PWMs +---------- + +Legacy users can request a PWM device using pwm_request() and free it +after usage with pwm_free(). + +New users should use the pwm_get() function and pass to it the consumer +device or a consumer name. pwm_put() is used to free the PWM device. Managed +variants of the getter, devm_pwm_get() and devm_fwnode_pwm_get(), also exist. + +After being requested, a PWM has to be configured using:: + + int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state); + +This API controls both the PWM period/duty_cycle config and the +enable/disable state. + +As a consumer, don't rely on the output's state for a disabled PWM. If it's +easily possible, drivers are supposed to emit the inactive state, but some +drivers cannot. If you rely on getting the inactive state, use .duty_cycle=0, +.enabled=true. + +There is also a usage_power setting: If set, the PWM driver is only required to +maintain the power output but has more freedom regarding signal form. +If supported by the driver, the signal can be optimized, for example to improve +EMI by phase shifting the individual channels of a chip. + +The pwm_config(), pwm_enable() and pwm_disable() functions are just wrappers +around pwm_apply_state() and should not be used if the user wants to change +several parameter at once. For example, if you see pwm_config() and +pwm_{enable,disable}() calls in the same function, this probably means you +should switch to pwm_apply_state(). + +The PWM user API also allows one to query the PWM state that was passed to the +last invocation of pwm_apply_state() using pwm_get_state(). Note this is +different to what the driver has actually implemented if the request cannot be +satisfied exactly with the hardware in use. There is currently no way for +consumers to get the actually implemented settings. + +In addition to the PWM state, the PWM API also exposes PWM arguments, which +are the reference PWM config one should use on this PWM. +PWM arguments are usually platform-specific and allows the PWM user to only +care about dutycycle relatively to the full period (like, duty = 50% of the +period). struct pwm_args contains 2 fields (period and polarity) and should +be used to set the initial PWM config (usually done in the probe function +of the PWM user). PWM arguments are retrieved with pwm_get_args(). + +All consumers should really be reconfiguring the PWM upon resume as +appropriate. This is the only way to ensure that everything is resumed in +the proper order. + +Using PWMs with the sysfs interface +----------------------------------- + +If CONFIG_SYSFS is enabled in your kernel configuration a simple sysfs +interface is provided to use the PWMs from userspace. It is exposed at +/sys/class/pwm/. Each probed PWM controller/chip will be exported as +pwmchipN, where N is the base of the PWM chip. Inside the directory you +will find: + + npwm + The number of PWM channels this chip supports (read-only). + + export + Exports a PWM channel for use with sysfs (write-only). + + unexport + Unexports a PWM channel from sysfs (write-only). + +The PWM channels are numbered using a per-chip index from 0 to npwm-1. + +When a PWM channel is exported a pwmX directory will be created in the +pwmchipN directory it is associated with, where X is the number of the +channel that was exported. The following properties will then be available: + + period + The total period of the PWM signal (read/write). + Value is in nanoseconds and is the sum of the active and inactive + time of the PWM. + + duty_cycle + The active time of the PWM signal (read/write). + Value is in nanoseconds and must be less than the period. + + polarity + Changes the polarity of the PWM signal (read/write). + Writes to this property only work if the PWM chip supports changing + the polarity. The polarity can only be changed if the PWM is not + enabled. Value is the string "normal" or "inversed". + + enable + Enable/disable the PWM signal (read/write). + + - 0 - disabled + - 1 - enabled + +Implementing a PWM driver +------------------------- + +Currently there are two ways to implement pwm drivers. Traditionally +there only has been the barebone API meaning that each driver has +to implement the pwm_*() functions itself. This means that it's impossible +to have multiple PWM drivers in the system. For this reason it's mandatory +for new drivers to use the generic PWM framework. + +A new PWM controller/chip can be added using pwmchip_add() and removed +again with pwmchip_remove(). pwmchip_add() takes a filled in struct +pwm_chip as argument which provides a description of the PWM chip, the +number of PWM devices provided by the chip and the chip-specific +implementation of the supported PWM operations to the framework. + +When implementing polarity support in a PWM driver, make sure to respect the +signal conventions in the PWM framework. By definition, normal polarity +characterizes a signal starts high for the duration of the duty cycle and +goes low for the remainder of the period. Conversely, a signal with inversed +polarity starts low for the duration of the duty cycle and goes high for the +remainder of the period. + +Drivers are encouraged to implement ->apply() instead of the legacy +->enable(), ->disable() and ->config() methods. Doing that should provide +atomicity in the PWM config workflow, which is required when the PWM controls +a critical device (like a regulator). + +The implementation of ->get_state() (a method used to retrieve initial PWM +state) is also encouraged for the same reason: letting the PWM user know +about the current PWM state would allow him to avoid glitches. + +Drivers should not implement any power management. In other words, +consumers should implement it as described in the "Using PWMs" section. + +Locking +------- + +The PWM core list manipulations are protected by a mutex, so pwm_request() +and pwm_free() may not be called from an atomic context. Currently the +PWM core does not enforce any locking to pwm_enable(), pwm_disable() and +pwm_config(), so the calling context is currently driver specific. This +is an issue derived from the former barebone API and should be fixed soon. + +Helpers +------- + +Currently a PWM can only be configured with period_ns and duty_ns. For several +use cases freq_hz and duty_percent might be better. Instead of calculating +this in your driver please consider adding appropriate helpers to the framework. |