aboutsummaryrefslogtreecommitdiff
path: root/Documentation/driver-api/clk.rst
diff options
context:
space:
mode:
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
commit5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch)
treecc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/driver-api/clk.rst
downloadlinux-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/clk.rst')
-rw-r--r--Documentation/driver-api/clk.rst307
1 files changed, 307 insertions, 0 deletions
diff --git a/Documentation/driver-api/clk.rst b/Documentation/driver-api/clk.rst
new file mode 100644
index 000000000..3cad45d14
--- /dev/null
+++ b/Documentation/driver-api/clk.rst
@@ -0,0 +1,307 @@
+========================
+The Common Clk Framework
+========================
+
+:Author: Mike Turquette <mturquette@ti.com>
+
+This document endeavours to explain the common clk framework details,
+and how to port a platform over to this framework. It is not yet a
+detailed explanation of the clock api in include/linux/clk.h, but
+perhaps someday it will include that information.
+
+Introduction and interface split
+================================
+
+The common clk framework is an interface to control the clock nodes
+available on various devices today. This may come in the form of clock
+gating, rate adjustment, muxing or other operations. This framework is
+enabled with the CONFIG_COMMON_CLK option.
+
+The interface itself is divided into two halves, each shielded from the
+details of its counterpart. First is the common definition of struct
+clk which unifies the framework-level accounting and infrastructure that
+has traditionally been duplicated across a variety of platforms. Second
+is a common implementation of the clk.h api, defined in
+drivers/clk/clk.c. Finally there is struct clk_ops, whose operations
+are invoked by the clk api implementation.
+
+The second half of the interface is comprised of the hardware-specific
+callbacks registered with struct clk_ops and the corresponding
+hardware-specific structures needed to model a particular clock. For
+the remainder of this document any reference to a callback in struct
+clk_ops, such as .enable or .set_rate, implies the hardware-specific
+implementation of that code. Likewise, references to struct clk_foo
+serve as a convenient shorthand for the implementation of the
+hardware-specific bits for the hypothetical "foo" hardware.
+
+Tying the two halves of this interface together is struct clk_hw, which
+is defined in struct clk_foo and pointed to within struct clk_core. This
+allows for easy navigation between the two discrete halves of the common
+clock interface.
+
+Common data structures and api
+==============================
+
+Below is the common struct clk_core definition from
+drivers/clk/clk.c, modified for brevity::
+
+ struct clk_core {
+ const char *name;
+ const struct clk_ops *ops;
+ struct clk_hw *hw;
+ struct module *owner;
+ struct clk_core *parent;
+ const char **parent_names;
+ struct clk_core **parents;
+ u8 num_parents;
+ u8 new_parent_index;
+ ...
+ };
+
+The members above make up the core of the clk tree topology. The clk
+api itself defines several driver-facing functions which operate on
+struct clk. That api is documented in include/linux/clk.h.
+
+Platforms and devices utilizing the common struct clk_core use the struct
+clk_ops pointer in struct clk_core to perform the hardware-specific parts of
+the operations defined in clk-provider.h::
+
+ struct clk_ops {
+ int (*prepare)(struct clk_hw *hw);
+ void (*unprepare)(struct clk_hw *hw);
+ int (*is_prepared)(struct clk_hw *hw);
+ void (*unprepare_unused)(struct clk_hw *hw);
+ int (*enable)(struct clk_hw *hw);
+ void (*disable)(struct clk_hw *hw);
+ int (*is_enabled)(struct clk_hw *hw);
+ void (*disable_unused)(struct clk_hw *hw);
+ unsigned long (*recalc_rate)(struct clk_hw *hw,
+ unsigned long parent_rate);
+ long (*round_rate)(struct clk_hw *hw,
+ unsigned long rate,
+ unsigned long *parent_rate);
+ int (*determine_rate)(struct clk_hw *hw,
+ struct clk_rate_request *req);
+ int (*set_parent)(struct clk_hw *hw, u8 index);
+ u8 (*get_parent)(struct clk_hw *hw);
+ int (*set_rate)(struct clk_hw *hw,
+ unsigned long rate,
+ unsigned long parent_rate);
+ int (*set_rate_and_parent)(struct clk_hw *hw,
+ unsigned long rate,
+ unsigned long parent_rate,
+ u8 index);
+ unsigned long (*recalc_accuracy)(struct clk_hw *hw,
+ unsigned long parent_accuracy);
+ int (*get_phase)(struct clk_hw *hw);
+ int (*set_phase)(struct clk_hw *hw, int degrees);
+ void (*init)(struct clk_hw *hw);
+ void (*debug_init)(struct clk_hw *hw,
+ struct dentry *dentry);
+ };
+
+Hardware clk implementations
+============================
+
+The strength of the common struct clk_core comes from its .ops and .hw pointers
+which abstract the details of struct clk from the hardware-specific bits, and
+vice versa. To illustrate consider the simple gateable clk implementation in
+drivers/clk/clk-gate.c::
+
+ struct clk_gate {
+ struct clk_hw hw;
+ void __iomem *reg;
+ u8 bit_idx;
+ ...
+ };
+
+struct clk_gate contains struct clk_hw hw as well as hardware-specific
+knowledge about which register and bit controls this clk's gating.
+Nothing about clock topology or accounting, such as enable_count or
+notifier_count, is needed here. That is all handled by the common
+framework code and struct clk_core.
+
+Let's walk through enabling this clk from driver code::
+
+ struct clk *clk;
+ clk = clk_get(NULL, "my_gateable_clk");
+
+ clk_prepare(clk);
+ clk_enable(clk);
+
+The call graph for clk_enable is very simple::
+
+ clk_enable(clk);
+ clk->ops->enable(clk->hw);
+ [resolves to...]
+ clk_gate_enable(hw);
+ [resolves struct clk gate with to_clk_gate(hw)]
+ clk_gate_set_bit(gate);
+
+And the definition of clk_gate_set_bit::
+
+ static void clk_gate_set_bit(struct clk_gate *gate)
+ {
+ u32 reg;
+
+ reg = __raw_readl(gate->reg);
+ reg |= BIT(gate->bit_idx);
+ writel(reg, gate->reg);
+ }
+
+Note that to_clk_gate is defined as::
+
+ #define to_clk_gate(_hw) container_of(_hw, struct clk_gate, hw)
+
+This pattern of abstraction is used for every clock hardware
+representation.
+
+Supporting your own clk hardware
+================================
+
+When implementing support for a new type of clock it is only necessary to
+include the following header::
+
+ #include <linux/clk-provider.h>
+
+To construct a clk hardware structure for your platform you must define
+the following::
+
+ struct clk_foo {
+ struct clk_hw hw;
+ ... hardware specific data goes here ...
+ };
+
+To take advantage of your data you'll need to support valid operations
+for your clk::
+
+ struct clk_ops clk_foo_ops = {
+ .enable = &clk_foo_enable,
+ .disable = &clk_foo_disable,
+ };
+
+Implement the above functions using container_of::
+
+ #define to_clk_foo(_hw) container_of(_hw, struct clk_foo, hw)
+
+ int clk_foo_enable(struct clk_hw *hw)
+ {
+ struct clk_foo *foo;
+
+ foo = to_clk_foo(hw);
+
+ ... perform magic on foo ...
+
+ return 0;
+ };
+
+Below is a matrix detailing which clk_ops are mandatory based upon the
+hardware capabilities of that clock. A cell marked as "y" means
+mandatory, a cell marked as "n" implies that either including that
+callback is invalid or otherwise unnecessary. Empty cells are either
+optional or must be evaluated on a case-by-case basis.
+
+.. table:: clock hardware characteristics
+
+ +----------------+------+-------------+---------------+-------------+------+
+ | | gate | change rate | single parent | multiplexer | root |
+ +================+======+=============+===============+=============+======+
+ |.prepare | | | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ |.unprepare | | | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ +----------------+------+-------------+---------------+-------------+------+
+ |.enable | y | | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ |.disable | y | | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ |.is_enabled | y | | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ +----------------+------+-------------+---------------+-------------+------+
+ |.recalc_rate | | y | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ |.round_rate | | y [1]_ | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ |.determine_rate | | y [1]_ | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ |.set_rate | | y | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ +----------------+------+-------------+---------------+-------------+------+
+ |.set_parent | | | n | y | n |
+ +----------------+------+-------------+---------------+-------------+------+
+ |.get_parent | | | n | y | n |
+ +----------------+------+-------------+---------------+-------------+------+
+ +----------------+------+-------------+---------------+-------------+------+
+ |.recalc_accuracy| | | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+ +----------------+------+-------------+---------------+-------------+------+
+ |.init | | | | | |
+ +----------------+------+-------------+---------------+-------------+------+
+
+.. [1] either one of round_rate or determine_rate is required.
+
+Finally, register your clock at run-time with a hardware-specific
+registration function. This function simply populates struct clk_foo's
+data and then passes the common struct clk parameters to the framework
+with a call to::
+
+ clk_register(...)
+
+See the basic clock types in ``drivers/clk/clk-*.c`` for examples.
+
+Disabling clock gating of unused clocks
+=======================================
+
+Sometimes during development it can be useful to be able to bypass the
+default disabling of unused clocks. For example, if drivers aren't enabling
+clocks properly but rely on them being on from the bootloader, bypassing
+the disabling means that the driver will remain functional while the issues
+are sorted out.
+
+To bypass this disabling, include "clk_ignore_unused" in the bootargs to the
+kernel.
+
+Locking
+=======
+
+The common clock framework uses two global locks, the prepare lock and the
+enable lock.
+
+The enable lock is a spinlock and is held across calls to the .enable,
+.disable operations. Those operations are thus not allowed to sleep,
+and calls to the clk_enable(), clk_disable() API functions are allowed in
+atomic context.
+
+For clk_is_enabled() API, it is also designed to be allowed to be used in
+atomic context. However, it doesn't really make any sense to hold the enable
+lock in core, unless you want to do something else with the information of
+the enable state with that lock held. Otherwise, seeing if a clk is enabled is
+a one-shot read of the enabled state, which could just as easily change after
+the function returns because the lock is released. Thus the user of this API
+needs to handle synchronizing the read of the state with whatever they're
+using it for to make sure that the enable state doesn't change during that
+time.
+
+The prepare lock is a mutex and is held across calls to all other operations.
+All those operations are allowed to sleep, and calls to the corresponding API
+functions are not allowed in atomic context.
+
+This effectively divides operations in two groups from a locking perspective.
+
+Drivers don't need to manually protect resources shared between the operations
+of one group, regardless of whether those resources are shared by multiple
+clocks or not. However, access to resources that are shared between operations
+of the two groups needs to be protected by the drivers. An example of such a
+resource would be a register that controls both the clock rate and the clock
+enable/disable state.
+
+The clock framework is reentrant, in that a driver is allowed to call clock
+framework functions from within its implementation of clock operations. This
+can for instance cause a .set_rate operation of one clock being called from
+within the .set_rate operation of another clock. This case must be considered
+in the driver implementations, but the code flow is usually controlled by the
+driver in that case.
+
+Note that locking must also be considered when code outside of the common
+clock framework needs to access resources used by the clock operations. This
+is considered out of scope of this document.