posix-clock.h

  1/* SPDX-License-Identifier: GPL-2.0-or-later */
  2/*
  3 * posix-clock.h - support for dynamic clock devices
  4 *
  5 * Copyright (C) 2010 OMICRON electronics GmbH
  6 */
  7#ifndef _LINUX_POSIX_CLOCK_H_
  8#define _LINUX_POSIX_CLOCK_H_
  9
 10#include <linux/cdev.h>
 11#include <linux/fs.h>
 12#include <linux/poll.h>
 13#include <linux/posix-timers.h>
 14#include <linux/rwsem.h>
 15
 16struct posix_clock;
 17struct posix_clock_context;
 18
 19/**
 20 * struct posix_clock_operations - functional interface to the clock
 21 *
 22 * Every posix clock is represented by a character device. Drivers may
 23 * optionally offer extended capabilities by implementing the
 24 * character device methods. The character device file operations are
 25 * first handled by the clock device layer, then passed on to the
 26 * driver by calling these functions.
 27 *
 28 * @owner:          The clock driver should set to THIS_MODULE
 29 * @clock_adjtime:  Adjust the clock
 30 * @clock_gettime:  Read the current time
 31 * @clock_getres:   Get the clock resolution
 32 * @clock_settime:  Set the current time value
 33 * @open:           Optional character device open method
 34 * @release:        Optional character device release method
 35 * @ioctl:          Optional character device ioctl method
 36 * @read:           Optional character device read method
 37 * @poll:           Optional character device poll method
 38 */
 39struct posix_clock_operations {
 40	struct module *owner;
 41
 42	int  (*clock_adjtime)(struct posix_clock *pc, struct __kernel_timex *tx);
 43
 44	int  (*clock_gettime)(struct posix_clock *pc, struct timespec64 *ts);
 45
 46	int  (*clock_getres) (struct posix_clock *pc, struct timespec64 *ts);
 47
 48	int  (*clock_settime)(struct posix_clock *pc,
 49			      const struct timespec64 *ts);
 50
 51	/*
 52	 * Optional character device methods:
 53	 */
 54	long (*ioctl)(struct posix_clock_context *pccontext, unsigned int cmd,
 55		      unsigned long arg);
 56
 57	int (*open)(struct posix_clock_context *pccontext, fmode_t f_mode);
 58
 59	__poll_t (*poll)(struct posix_clock_context *pccontext, struct file *file,
 60			 poll_table *wait);
 61
 62	int (*release)(struct posix_clock_context *pccontext);
 63
 64	ssize_t (*read)(struct posix_clock_context *pccontext, uint flags,
 65			char __user *buf, size_t cnt);
 66};
 67
 68/**
 69 * struct posix_clock - represents a dynamic posix clock
 70 *
 71 * @ops:     Functional interface to the clock
 72 * @cdev:    Character device instance for this clock
 73 * @dev:     Pointer to the clock's device.
 74 * @rwsem:   Protects the 'zombie' field from concurrent access.
 75 * @zombie:  If 'zombie' is true, then the hardware has disappeared.
 76 *
 77 * Drivers should embed their struct posix_clock within a private
 78 * structure, obtaining a reference to it during callbacks using
 79 * container_of().
 80 *
 81 * Drivers should supply an initialized but not exposed struct device
 82 * to posix_clock_register(). It is used to manage lifetime of the
 83 * driver's private structure. It's 'release' field should be set to
 84 * a release function for this private structure.
 85 */
 86struct posix_clock {
 87	struct posix_clock_operations ops;
 88	struct cdev cdev;
 89	struct device *dev;
 90	struct rw_semaphore rwsem;
 91	bool zombie;
 92};
 93
 94/**
 95 * struct posix_clock_context - represents clock file operations context
 96 *
 97 * @clk:              Pointer to the clock
 98 * @fp:               Pointer to the file used to open the clock
 99 * @private_clkdata:  Pointer to user data
100 *
101 * Drivers should use struct posix_clock_context during specific character
102 * device file operation methods to access the posix clock. In particular,
103 * the file pointer can be used to verify correct access mode for ioctl()
104 * calls.
105 *
106 * Drivers can store a private data structure during the open operation
107 * if they have specific information that is required in other file
108 * operations.
109 */
110struct posix_clock_context {
111	struct posix_clock *clk;
112	struct file *fp;
113	void *private_clkdata;
114};
115
116/**
117 * posix_clock_register() - register a new clock
118 * @clk:   Pointer to the clock. Caller must provide 'ops' field
119 * @dev:   Pointer to the initialized device. Caller must provide
120 *         'release' field
121 *
122 * A clock driver calls this function to register itself with the
123 * clock device subsystem. If 'clk' points to dynamically allocated
124 * memory, then the caller must provide a 'release' function to free
125 * that memory.
126 *
127 * Returns zero on success, non-zero otherwise.
128 */
129int posix_clock_register(struct posix_clock *clk, struct device *dev);
130
131/**
132 * posix_clock_unregister() - unregister a clock
133 * @clk: Clock instance previously registered via posix_clock_register()
134 *
135 * A clock driver calls this function to remove itself from the clock
136 * device subsystem. The posix_clock itself will remain (in an
137 * inactive state) until its reference count drops to zero, at which
138 * point it will be deallocated with its 'release' method.
139 */
140void posix_clock_unregister(struct posix_clock *clk);
141
142#endif