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/* SPDX-License-Identifier: GPL-2.0-or-later */
* posix-clock.h - support for dynamic clock devices
* Copyright (C) 2010 OMICRON electronics GmbH
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/posix-timers.h>
#include <linux/rwsem.h>
struct posix_clock;
* struct posix_clock_operations - functional interface to the clock
* Every posix clock is represented by a character device. Drivers may
* optionally offer extended capabilities by implementing the
* character device methods. The character device file operations are
* first handled by the clock device layer, then passed on to the
* driver by calling these functions.
* @owner: The clock driver should set to THIS_MODULE
* @clock_adjtime: Adjust the clock
* @clock_gettime: Read the current time
* @clock_getres: Get the clock resolution
* @clock_settime: Set the current time value
* @open: Optional character device open method
* @release: Optional character device release method
* @ioctl: Optional character device ioctl method
* @read: Optional character device read method
* @poll: Optional character device poll method
struct posix_clock_operations {
struct module *owner;
int (*clock_adjtime)(struct posix_clock *pc, struct __kernel_timex *tx);
int (*clock_gettime)(struct posix_clock *pc, struct timespec64 *ts);
int (*clock_getres) (struct posix_clock *pc, struct timespec64 *ts);
int (*clock_settime)(struct posix_clock *pc,
const struct timespec64 *ts);
* Optional character device methods:
long (*ioctl) (struct posix_clock *pc,
unsigned int cmd, unsigned long arg);
int (*open) (struct posix_clock *pc, fmode_t f_mode);
__poll_t (*poll) (struct posix_clock *pc,
struct file *file, poll_table *wait);
int (*release) (struct posix_clock *pc);
ssize_t (*read) (struct posix_clock *pc,
uint flags, char __user *buf, size_t cnt);
* struct posix_clock - represents a dynamic posix clock
* @ops: Functional interface to the clock
* @cdev: Character device instance for this clock
* @dev: Pointer to the clock's device.
* @rwsem: Protects the 'zombie' field from concurrent access.
* @zombie: If 'zombie' is true, then the hardware has disappeared.
* Drivers should embed their struct posix_clock within a private
* structure, obtaining a reference to it during callbacks using
* container_of().
* Drivers should supply an initialized but not exposed struct device
* to posix_clock_register(). It is used to manage lifetime of the
* driver's private structure. It's 'release' field should be set to
* a release function for this private structure.
struct posix_clock {
struct posix_clock_operations ops;
struct cdev cdev;
struct device *dev;
struct rw_semaphore rwsem;
bool zombie;
* posix_clock_register() - register a new clock
* @clk: Pointer to the clock. Caller must provide 'ops' field
* @dev: Pointer to the initialized device. Caller must provide
* 'release' field
* A clock driver calls this function to register itself with the
* clock device subsystem. If 'clk' points to dynamically allocated
* memory, then the caller must provide a 'release' function to free
* that memory.
* Returns zero on success, non-zero otherwise.
int posix_clock_register(struct posix_clock *clk, struct device *dev);
* posix_clock_unregister() - unregister a clock
* @clk: Clock instance previously registered via posix_clock_register()
* A clock driver calls this function to remove itself from the clock
* device subsystem. The posix_clock itself will remain (in an
* inactive state) until its reference count drops to zero, at which
* point it will be deallocated with its 'release' method.
void posix_clock_unregister(struct posix_clock *clk);