xref: /openbmc/linux/include/linux/posix-clock.h (revision a33121e5)
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 
16 struct posix_clock;
17 
18 /**
19  * struct posix_clock_operations - functional interface to the clock
20  *
21  * Every posix clock is represented by a character device. Drivers may
22  * optionally offer extended capabilities by implementing the
23  * character device methods. The character device file operations are
24  * first handled by the clock device layer, then passed on to the
25  * driver by calling these functions.
26  *
27  * @owner:          The clock driver should set to THIS_MODULE
28  * @clock_adjtime:  Adjust the clock
29  * @clock_gettime:  Read the current time
30  * @clock_getres:   Get the clock resolution
31  * @clock_settime:  Set the current time value
32  * @open:           Optional character device open method
33  * @release:        Optional character device release method
34  * @ioctl:          Optional character device ioctl method
35  * @read:           Optional character device read method
36  * @poll:           Optional character device poll method
37  */
38 struct posix_clock_operations {
39 	struct module *owner;
40 
41 	int  (*clock_adjtime)(struct posix_clock *pc, struct __kernel_timex *tx);
42 
43 	int  (*clock_gettime)(struct posix_clock *pc, struct timespec64 *ts);
44 
45 	int  (*clock_getres) (struct posix_clock *pc, struct timespec64 *ts);
46 
47 	int  (*clock_settime)(struct posix_clock *pc,
48 			      const struct timespec64 *ts);
49 
50 	/*
51 	 * Optional character device methods:
52 	 */
53 	long    (*ioctl)   (struct posix_clock *pc,
54 			    unsigned int cmd, unsigned long arg);
55 
56 	int     (*open)    (struct posix_clock *pc, fmode_t f_mode);
57 
58 	__poll_t (*poll)   (struct posix_clock *pc,
59 			    struct file *file, poll_table *wait);
60 
61 	int     (*release) (struct posix_clock *pc);
62 
63 	ssize_t (*read)    (struct posix_clock *pc,
64 			    uint flags, char __user *buf, size_t cnt);
65 };
66 
67 /**
68  * struct posix_clock - represents a dynamic posix clock
69  *
70  * @ops:     Functional interface to the clock
71  * @cdev:    Character device instance for this clock
72  * @dev:     Pointer to the clock's device.
73  * @rwsem:   Protects the 'zombie' field from concurrent access.
74  * @zombie:  If 'zombie' is true, then the hardware has disappeared.
75  *
76  * Drivers should embed their struct posix_clock within a private
77  * structure, obtaining a reference to it during callbacks using
78  * container_of().
79  *
80  * Drivers should supply an initialized but not exposed struct device
81  * to posix_clock_register(). It is used to manage lifetime of the
82  * driver's private structure. It's 'release' field should be set to
83  * a release function for this private structure.
84  */
85 struct posix_clock {
86 	struct posix_clock_operations ops;
87 	struct cdev cdev;
88 	struct device *dev;
89 	struct rw_semaphore rwsem;
90 	bool zombie;
91 };
92 
93 /**
94  * posix_clock_register() - register a new clock
95  * @clk:   Pointer to the clock. Caller must provide 'ops' field
96  * @dev:   Pointer to the initialized device. Caller must provide
97  *         'release' field
98  *
99  * A clock driver calls this function to register itself with the
100  * clock device subsystem. If 'clk' points to dynamically allocated
101  * memory, then the caller must provide a 'release' function to free
102  * that memory.
103  *
104  * Returns zero on success, non-zero otherwise.
105  */
106 int posix_clock_register(struct posix_clock *clk, struct device *dev);
107 
108 /**
109  * posix_clock_unregister() - unregister a clock
110  * @clk: Clock instance previously registered via posix_clock_register()
111  *
112  * A clock driver calls this function to remove itself from the clock
113  * device subsystem. The posix_clock itself will remain (in an
114  * inactive state) until its reference count drops to zero, at which
115  * point it will be deallocated with its 'release' method.
116  */
117 void posix_clock_unregister(struct posix_clock *clk);
118 
119 #endif
120