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 struct 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  */
39 struct 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  */
86 struct 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  * @private_clkdata:  Pointer to user data
99  *
100  * Drivers should use struct posix_clock_context during specific character
101  * device file operation methods to access the posix clock.
102  *
103  * Drivers can store a private data structure during the open operation
104  * if they have specific information that is required in other file
105  * operations.
106  */
107 struct posix_clock_context {
108 	struct posix_clock *clk;
109 	void *private_clkdata;
110 };
111 
112 /**
113  * posix_clock_register() - register a new clock
114  * @clk:   Pointer to the clock. Caller must provide 'ops' field
115  * @dev:   Pointer to the initialized device. Caller must provide
116  *         'release' field
117  *
118  * A clock driver calls this function to register itself with the
119  * clock device subsystem. If 'clk' points to dynamically allocated
120  * memory, then the caller must provide a 'release' function to free
121  * that memory.
122  *
123  * Returns zero on success, non-zero otherwise.
124  */
125 int posix_clock_register(struct posix_clock *clk, struct device *dev);
126 
127 /**
128  * posix_clock_unregister() - unregister a clock
129  * @clk: Clock instance previously registered via posix_clock_register()
130  *
131  * A clock driver calls this function to remove itself from the clock
132  * device subsystem. The posix_clock itself will remain (in an
133  * inactive state) until its reference count drops to zero, at which
134  * point it will be deallocated with its 'release' method.
135  */
136 void posix_clock_unregister(struct posix_clock *clk);
137 
138 #endif
139