1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (c) 2025 Greg Kroah-Hartman <[email protected]>
4 * Copyright (c) 2025 The Linux Foundation
5 *
6 * A "simple" faux bus that allows devices to be created and added
7 * automatically to it. This is to be used whenever you need to create a
8 * device that is not associated with any "real" system resources, and do
9 * not want to have to deal with a bus/driver binding logic. It is
10 * intended to be very simple, with only a create and a destroy function
11 * available.
12 */
13 #include <linux/err.h>
14 #include <linux/init.h>
15 #include <linux/slab.h>
16 #include <linux/string.h>
17 #include <linux/container_of.h>
18 #include <linux/device/faux.h>
19 #include "base.h"
20
21 /*
22 * Internal wrapper structure so we can hold a pointer to the
23 * faux_device_ops for this device.
24 */
25 struct faux_object {
26 struct faux_device faux_dev;
27 const struct faux_device_ops *faux_ops;
28 };
29 #define to_faux_object(dev) container_of_const(dev, struct faux_object, faux_dev.dev)
30
31 static struct device faux_bus_root = {
32 .init_name = "faux",
33 };
34
faux_match(struct device * dev,const struct device_driver * drv)35 static int faux_match(struct device *dev, const struct device_driver *drv)
36 {
37 /* Match always succeeds, we only have one driver */
38 return 1;
39 }
40
faux_probe(struct device * dev)41 static int faux_probe(struct device *dev)
42 {
43 struct faux_object *faux_obj = to_faux_object(dev);
44 struct faux_device *faux_dev = &faux_obj->faux_dev;
45 const struct faux_device_ops *faux_ops = faux_obj->faux_ops;
46 int ret = 0;
47
48 if (faux_ops && faux_ops->probe)
49 ret = faux_ops->probe(faux_dev);
50
51 return ret;
52 }
53
faux_remove(struct device * dev)54 static void faux_remove(struct device *dev)
55 {
56 struct faux_object *faux_obj = to_faux_object(dev);
57 struct faux_device *faux_dev = &faux_obj->faux_dev;
58 const struct faux_device_ops *faux_ops = faux_obj->faux_ops;
59
60 if (faux_ops && faux_ops->remove)
61 faux_ops->remove(faux_dev);
62 }
63
64 static const struct bus_type faux_bus_type = {
65 .name = "faux",
66 .match = faux_match,
67 .probe = faux_probe,
68 .remove = faux_remove,
69 };
70
71 static struct device_driver faux_driver = {
72 .name = "faux_driver",
73 .bus = &faux_bus_type,
74 .probe_type = PROBE_FORCE_SYNCHRONOUS,
75 };
76
faux_device_release(struct device * dev)77 static void faux_device_release(struct device *dev)
78 {
79 struct faux_object *faux_obj = to_faux_object(dev);
80
81 kfree(faux_obj);
82 }
83
84 /**
85 * faux_device_create_with_groups - Create and register with the driver
86 * core a faux device and populate the device with an initial
87 * set of sysfs attributes.
88 * @name: The name of the device we are adding, must be unique for
89 * all faux devices.
90 * @parent: Pointer to a potential parent struct device. If set to
91 * NULL, the device will be created in the "root" of the faux
92 * device tree in sysfs.
93 * @faux_ops: struct faux_device_ops that the new device will call back
94 * into, can be NULL.
95 * @groups: The set of sysfs attributes that will be created for this
96 * device when it is registered with the driver core.
97 *
98 * Create a new faux device and register it in the driver core properly.
99 * If present, callbacks in @faux_ops will be called with the device that
100 * for the caller to do something with at the proper time given the
101 * device's lifecycle.
102 *
103 * Note, when this function is called, the functions specified in struct
104 * faux_ops can be called before the function returns, so be prepared for
105 * everything to be properly initialized before that point in time.
106 *
107 * Return:
108 * * NULL if an error happened with creating the device
109 * * pointer to a valid struct faux_device that is registered with sysfs
110 */
faux_device_create_with_groups(const char * name,struct device * parent,const struct faux_device_ops * faux_ops,const struct attribute_group ** groups)111 struct faux_device *faux_device_create_with_groups(const char *name,
112 struct device *parent,
113 const struct faux_device_ops *faux_ops,
114 const struct attribute_group **groups)
115 {
116 struct faux_object *faux_obj;
117 struct faux_device *faux_dev;
118 struct device *dev;
119 int ret;
120
121 faux_obj = kzalloc(sizeof(*faux_obj), GFP_KERNEL);
122 if (!faux_obj)
123 return NULL;
124
125 /* Save off the callbacks so we can use them in the future */
126 faux_obj->faux_ops = faux_ops;
127
128 /* Initialize the device portion and register it with the driver core */
129 faux_dev = &faux_obj->faux_dev;
130 dev = &faux_dev->dev;
131
132 device_initialize(dev);
133 dev->release = faux_device_release;
134 if (parent)
135 dev->parent = parent;
136 else
137 dev->parent = &faux_bus_root;
138 dev->bus = &faux_bus_type;
139 dev->groups = groups;
140 dev_set_name(dev, "%s", name);
141
142 ret = device_add(dev);
143 if (ret) {
144 pr_err("%s: device_add for faux device '%s' failed with %d\n",
145 __func__, name, ret);
146 put_device(dev);
147 return NULL;
148 }
149
150 return faux_dev;
151 }
152 EXPORT_SYMBOL_GPL(faux_device_create_with_groups);
153
154 /**
155 * faux_device_create - create and register with the driver core a faux device
156 * @name: The name of the device we are adding, must be unique for all
157 * faux devices.
158 * @parent: Pointer to a potential parent struct device. If set to
159 * NULL, the device will be created in the "root" of the faux
160 * device tree in sysfs.
161 * @faux_ops: struct faux_device_ops that the new device will call back
162 * into, can be NULL.
163 *
164 * Create a new faux device and register it in the driver core properly.
165 * If present, callbacks in @faux_ops will be called with the device that
166 * for the caller to do something with at the proper time given the
167 * device's lifecycle.
168 *
169 * Note, when this function is called, the functions specified in struct
170 * faux_ops can be called before the function returns, so be prepared for
171 * everything to be properly initialized before that point in time.
172 *
173 * Return:
174 * * NULL if an error happened with creating the device
175 * * pointer to a valid struct faux_device that is registered with sysfs
176 */
faux_device_create(const char * name,struct device * parent,const struct faux_device_ops * faux_ops)177 struct faux_device *faux_device_create(const char *name,
178 struct device *parent,
179 const struct faux_device_ops *faux_ops)
180 {
181 return faux_device_create_with_groups(name, parent, faux_ops, NULL);
182 }
183 EXPORT_SYMBOL_GPL(faux_device_create);
184
185 /**
186 * faux_device_destroy - destroy a faux device
187 * @faux_dev: faux device to destroy
188 *
189 * Unregisters and cleans up a device that was created with a call to
190 * faux_device_create()
191 */
faux_device_destroy(struct faux_device * faux_dev)192 void faux_device_destroy(struct faux_device *faux_dev)
193 {
194 struct device *dev = &faux_dev->dev;
195
196 if (!faux_dev)
197 return;
198
199 device_del(dev);
200
201 /* The final put_device() will clean up the memory we allocated for this device. */
202 put_device(dev);
203 }
204 EXPORT_SYMBOL_GPL(faux_device_destroy);
205
faux_bus_init(void)206 int __init faux_bus_init(void)
207 {
208 int ret;
209
210 ret = device_register(&faux_bus_root);
211 if (ret) {
212 put_device(&faux_bus_root);
213 return ret;
214 }
215
216 ret = bus_register(&faux_bus_type);
217 if (ret)
218 goto error_bus;
219
220 ret = driver_register(&faux_driver);
221 if (ret)
222 goto error_driver;
223
224 return ret;
225
226 error_driver:
227 bus_unregister(&faux_bus_type);
228
229 error_bus:
230 device_unregister(&faux_bus_root);
231 return ret;
232 }
233