1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Telemetry communication for Wilco EC
4 *
5 * Copyright 2019 Google LLC
6 *
7 * The Wilco Embedded Controller is able to send telemetry data
8 * which is useful for enterprise applications. A daemon running on
9 * the OS sends a command to the EC via a write() to a char device,
10 * and can read the response with a read(). The write() request is
11 * verified by the driver to ensure that it is performing only one
12 * of the allowlisted commands, and that no extraneous data is
13 * being transmitted to the EC. The response is passed directly
14 * back to the reader with no modification.
15 *
16 * The character device will appear as /dev/wilco_telemN, where N
17 * is some small non-negative integer, starting with 0. Only one
18 * process may have the file descriptor open at a time. The calling
19 * userspace program needs to keep the device file descriptor open
20 * between the calls to write() and read() in order to preserve the
21 * response. Up to 32 bytes will be available for reading.
22 *
23 * For testing purposes, try requesting the EC's firmware build
24 * date, by sending the WILCO_EC_TELEM_GET_VERSION command with
25 * argument index=3. i.e. write [0x38, 0x00, 0x03]
26 * to the device node. An ASCII string of the build date is
27 * returned.
28 */
29
30 #include <linux/cdev.h>
31 #include <linux/device.h>
32 #include <linux/fs.h>
33 #include <linux/module.h>
34 #include <linux/platform_data/wilco-ec.h>
35 #include <linux/platform_device.h>
36 #include <linux/slab.h>
37 #include <linux/types.h>
38 #include <linux/uaccess.h>
39
40 #define TELEM_DEV_NAME "wilco_telem"
41 #define TELEM_CLASS_NAME TELEM_DEV_NAME
42 #define DRV_NAME TELEM_DEV_NAME
43 #define TELEM_DEV_NAME_FMT (TELEM_DEV_NAME "%d")
44 static struct class telem_class = {
45 .name = TELEM_CLASS_NAME,
46 };
47
48 /* Keep track of all the device numbers used. */
49 #define TELEM_MAX_DEV 128
50 static int telem_major;
51 static DEFINE_IDA(telem_ida);
52
53 /* EC telemetry command codes */
54 #define WILCO_EC_TELEM_GET_LOG 0x99
55 #define WILCO_EC_TELEM_GET_VERSION 0x38
56 #define WILCO_EC_TELEM_GET_FAN_INFO 0x2E
57 #define WILCO_EC_TELEM_GET_DIAG_INFO 0xFA
58 #define WILCO_EC_TELEM_GET_TEMP_INFO 0x95
59 #define WILCO_EC_TELEM_GET_TEMP_READ 0x2C
60 #define WILCO_EC_TELEM_GET_BATT_EXT_INFO 0x07
61 #define WILCO_EC_TELEM_GET_BATT_PPID_INFO 0x8A
62
63 #define TELEM_ARGS_SIZE_MAX 30
64
65 /*
66 * The following telem_args_get_* structs are embedded within the |args| field
67 * of wilco_ec_telem_request.
68 */
69
70 struct telem_args_get_log {
71 u8 log_type;
72 u8 log_index;
73 } __packed;
74
75 /*
76 * Get a piece of info about the EC firmware version:
77 * 0 = label
78 * 1 = svn_rev
79 * 2 = model_no
80 * 3 = build_date
81 * 4 = frio_version
82 */
83 struct telem_args_get_version {
84 u8 index;
85 } __packed;
86
87 struct telem_args_get_fan_info {
88 u8 command;
89 u8 fan_number;
90 u8 arg;
91 } __packed;
92
93 struct telem_args_get_diag_info {
94 u8 type;
95 u8 sub_type;
96 } __packed;
97
98 struct telem_args_get_temp_info {
99 u8 command;
100 u8 index;
101 u8 field;
102 u8 zone;
103 } __packed;
104
105 struct telem_args_get_temp_read {
106 u8 sensor_index;
107 } __packed;
108
109 struct telem_args_get_batt_ext_info {
110 u8 var_args[5];
111 } __packed;
112
113 struct telem_args_get_batt_ppid_info {
114 u8 always1; /* Should always be 1 */
115 } __packed;
116
117 /**
118 * struct wilco_ec_telem_request - Telemetry command and arguments sent to EC.
119 * @command: One of WILCO_EC_TELEM_GET_* command codes.
120 * @reserved: Must be 0.
121 * @args: The first N bytes are one of telem_args_get_* structs, the rest is 0.
122 */
123 struct wilco_ec_telem_request {
124 u8 command;
125 u8 reserved;
126 union {
127 u8 buf[TELEM_ARGS_SIZE_MAX];
128 struct telem_args_get_log get_log;
129 struct telem_args_get_version get_version;
130 struct telem_args_get_fan_info get_fan_info;
131 struct telem_args_get_diag_info get_diag_info;
132 struct telem_args_get_temp_info get_temp_info;
133 struct telem_args_get_temp_read get_temp_read;
134 struct telem_args_get_batt_ext_info get_batt_ext_info;
135 struct telem_args_get_batt_ppid_info get_batt_ppid_info;
136 } args;
137 } __packed;
138
139 /**
140 * check_telem_request() - Ensure that a request from userspace is valid.
141 * @rq: Request buffer copied from userspace.
142 * @size: Number of bytes copied from userspace.
143 *
144 * Return: 0 if valid, -EINVAL if bad command or reserved byte is non-zero,
145 * -EMSGSIZE if the request is too long.
146 *
147 * We do not want to allow userspace to send arbitrary telemetry commands to
148 * the EC. Therefore we check to ensure that
149 * 1. The request follows the format of struct wilco_ec_telem_request.
150 * 2. The supplied command code is one of the allowlisted commands.
151 * 3. The request only contains the necessary data for the header and arguments.
152 */
check_telem_request(struct wilco_ec_telem_request * rq,size_t size)153 static int check_telem_request(struct wilco_ec_telem_request *rq,
154 size_t size)
155 {
156 size_t max_size = offsetof(struct wilco_ec_telem_request, args);
157
158 if (rq->reserved)
159 return -EINVAL;
160
161 switch (rq->command) {
162 case WILCO_EC_TELEM_GET_LOG:
163 max_size += sizeof(rq->args.get_log);
164 break;
165 case WILCO_EC_TELEM_GET_VERSION:
166 max_size += sizeof(rq->args.get_version);
167 break;
168 case WILCO_EC_TELEM_GET_FAN_INFO:
169 max_size += sizeof(rq->args.get_fan_info);
170 break;
171 case WILCO_EC_TELEM_GET_DIAG_INFO:
172 max_size += sizeof(rq->args.get_diag_info);
173 break;
174 case WILCO_EC_TELEM_GET_TEMP_INFO:
175 max_size += sizeof(rq->args.get_temp_info);
176 break;
177 case WILCO_EC_TELEM_GET_TEMP_READ:
178 max_size += sizeof(rq->args.get_temp_read);
179 break;
180 case WILCO_EC_TELEM_GET_BATT_EXT_INFO:
181 max_size += sizeof(rq->args.get_batt_ext_info);
182 break;
183 case WILCO_EC_TELEM_GET_BATT_PPID_INFO:
184 if (rq->args.get_batt_ppid_info.always1 != 1)
185 return -EINVAL;
186
187 max_size += sizeof(rq->args.get_batt_ppid_info);
188 break;
189 default:
190 return -EINVAL;
191 }
192
193 return (size <= max_size) ? 0 : -EMSGSIZE;
194 }
195
196 /**
197 * struct telem_device_data - Data for a Wilco EC device that queries telemetry.
198 * @cdev: Char dev that userspace reads and polls from.
199 * @dev: Device associated with the %cdev.
200 * @ec: Wilco EC that we will be communicating with using the mailbox interface.
201 * @available: Boolean of if the device can be opened.
202 */
203 struct telem_device_data {
204 struct device dev;
205 struct cdev cdev;
206 struct wilco_ec_device *ec;
207 atomic_t available;
208 };
209
210 #define TELEM_RESPONSE_SIZE EC_MAILBOX_DATA_SIZE
211
212 /**
213 * struct telem_session_data - Data that exists between open() and release().
214 * @dev_data: Pointer to get back to the device data and EC.
215 * @request: Command and arguments sent to EC.
216 * @response: Response buffer of data from EC.
217 * @has_msg: Is there data available to read from a previous write?
218 */
219 struct telem_session_data {
220 struct telem_device_data *dev_data;
221 struct wilco_ec_telem_request request;
222 u8 response[TELEM_RESPONSE_SIZE];
223 bool has_msg;
224 };
225
226 /**
227 * telem_open() - Callback for when the device node is opened.
228 * @inode: inode for this char device node.
229 * @filp: file for this char device node.
230 *
231 * We need to ensure that after writing a command to the device,
232 * the same userspace process reads the corresponding result.
233 * Therefore, we increment a refcount on opening the device, so that
234 * only one process can communicate with the EC at a time.
235 *
236 * Return: 0 on success, or negative error code on failure.
237 */
telem_open(struct inode * inode,struct file * filp)238 static int telem_open(struct inode *inode, struct file *filp)
239 {
240 struct telem_device_data *dev_data;
241 struct telem_session_data *sess_data;
242
243 /* Ensure device isn't already open */
244 dev_data = container_of(inode->i_cdev, struct telem_device_data, cdev);
245 if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
246 return -EBUSY;
247
248 get_device(&dev_data->dev);
249
250 sess_data = kzalloc(sizeof(*sess_data), GFP_KERNEL);
251 if (!sess_data) {
252 atomic_set(&dev_data->available, 1);
253 return -ENOMEM;
254 }
255 sess_data->dev_data = dev_data;
256 sess_data->has_msg = false;
257
258 stream_open(inode, filp);
259 filp->private_data = sess_data;
260
261 return 0;
262 }
263
telem_write(struct file * filp,const char __user * buf,size_t count,loff_t * pos)264 static ssize_t telem_write(struct file *filp, const char __user *buf,
265 size_t count, loff_t *pos)
266 {
267 struct telem_session_data *sess_data = filp->private_data;
268 struct wilco_ec_message msg = {};
269 int ret;
270
271 if (count > sizeof(sess_data->request))
272 return -EMSGSIZE;
273 memset(&sess_data->request, 0, sizeof(sess_data->request));
274 if (copy_from_user(&sess_data->request, buf, count))
275 return -EFAULT;
276 ret = check_telem_request(&sess_data->request, count);
277 if (ret < 0)
278 return ret;
279
280 memset(sess_data->response, 0, sizeof(sess_data->response));
281 msg.type = WILCO_EC_MSG_TELEMETRY;
282 msg.request_data = &sess_data->request;
283 msg.request_size = sizeof(sess_data->request);
284 msg.response_data = sess_data->response;
285 msg.response_size = sizeof(sess_data->response);
286
287 ret = wilco_ec_mailbox(sess_data->dev_data->ec, &msg);
288 if (ret < 0)
289 return ret;
290 if (ret != sizeof(sess_data->response))
291 return -EMSGSIZE;
292
293 sess_data->has_msg = true;
294
295 return count;
296 }
297
telem_read(struct file * filp,char __user * buf,size_t count,loff_t * pos)298 static ssize_t telem_read(struct file *filp, char __user *buf, size_t count,
299 loff_t *pos)
300 {
301 struct telem_session_data *sess_data = filp->private_data;
302
303 if (!sess_data->has_msg)
304 return -ENODATA;
305 if (count > sizeof(sess_data->response))
306 return -EINVAL;
307
308 if (copy_to_user(buf, sess_data->response, count))
309 return -EFAULT;
310
311 sess_data->has_msg = false;
312
313 return count;
314 }
315
telem_release(struct inode * inode,struct file * filp)316 static int telem_release(struct inode *inode, struct file *filp)
317 {
318 struct telem_session_data *sess_data = filp->private_data;
319
320 atomic_set(&sess_data->dev_data->available, 1);
321 put_device(&sess_data->dev_data->dev);
322 kfree(sess_data);
323
324 return 0;
325 }
326
327 static const struct file_operations telem_fops = {
328 .open = telem_open,
329 .write = telem_write,
330 .read = telem_read,
331 .release = telem_release,
332 .llseek = no_llseek,
333 .owner = THIS_MODULE,
334 };
335
336 /**
337 * telem_device_free() - Callback to free the telem_device_data structure.
338 * @d: The device embedded in our device data, which we have been ref counting.
339 *
340 * Once all open file descriptors are closed and the device has been removed,
341 * the refcount of the device will fall to 0 and this will be called.
342 */
telem_device_free(struct device * d)343 static void telem_device_free(struct device *d)
344 {
345 struct telem_device_data *dev_data;
346
347 dev_data = container_of(d, struct telem_device_data, dev);
348 kfree(dev_data);
349 }
350
351 /**
352 * telem_device_probe() - Callback when creating a new device.
353 * @pdev: platform device that we will be receiving telems from.
354 *
355 * This finds a free minor number for the device, allocates and initializes
356 * some device data, and creates a new device and char dev node.
357 *
358 * Return: 0 on success, negative error code on failure.
359 */
telem_device_probe(struct platform_device * pdev)360 static int telem_device_probe(struct platform_device *pdev)
361 {
362 struct telem_device_data *dev_data;
363 int error, minor;
364
365 /* Get the next available device number */
366 minor = ida_alloc_max(&telem_ida, TELEM_MAX_DEV-1, GFP_KERNEL);
367 if (minor < 0) {
368 error = minor;
369 dev_err(&pdev->dev, "Failed to find minor number: %d\n", error);
370 return error;
371 }
372
373 dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
374 if (!dev_data) {
375 ida_simple_remove(&telem_ida, minor);
376 return -ENOMEM;
377 }
378
379 /* Initialize the device data */
380 dev_data->ec = dev_get_platdata(&pdev->dev);
381 atomic_set(&dev_data->available, 1);
382 platform_set_drvdata(pdev, dev_data);
383
384 /* Initialize the device */
385 dev_data->dev.devt = MKDEV(telem_major, minor);
386 dev_data->dev.class = &telem_class;
387 dev_data->dev.release = telem_device_free;
388 dev_set_name(&dev_data->dev, TELEM_DEV_NAME_FMT, minor);
389 device_initialize(&dev_data->dev);
390
391 /* Initialize the character device and add it to userspace */;
392 cdev_init(&dev_data->cdev, &telem_fops);
393 error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
394 if (error) {
395 put_device(&dev_data->dev);
396 ida_simple_remove(&telem_ida, minor);
397 return error;
398 }
399
400 return 0;
401 }
402
telem_device_remove(struct platform_device * pdev)403 static int telem_device_remove(struct platform_device *pdev)
404 {
405 struct telem_device_data *dev_data = platform_get_drvdata(pdev);
406
407 cdev_device_del(&dev_data->cdev, &dev_data->dev);
408 ida_simple_remove(&telem_ida, MINOR(dev_data->dev.devt));
409 put_device(&dev_data->dev);
410
411 return 0;
412 }
413
414 static struct platform_driver telem_driver = {
415 .probe = telem_device_probe,
416 .remove = telem_device_remove,
417 .driver = {
418 .name = DRV_NAME,
419 },
420 };
421
telem_module_init(void)422 static int __init telem_module_init(void)
423 {
424 dev_t dev_num = 0;
425 int ret;
426
427 ret = class_register(&telem_class);
428 if (ret) {
429 pr_err(DRV_NAME ": Failed registering class: %d\n", ret);
430 return ret;
431 }
432
433 /* Request the kernel for device numbers, starting with minor=0 */
434 ret = alloc_chrdev_region(&dev_num, 0, TELEM_MAX_DEV, TELEM_DEV_NAME);
435 if (ret) {
436 pr_err(DRV_NAME ": Failed allocating dev numbers: %d\n", ret);
437 goto destroy_class;
438 }
439 telem_major = MAJOR(dev_num);
440
441 ret = platform_driver_register(&telem_driver);
442 if (ret < 0) {
443 pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
444 goto unregister_region;
445 }
446
447 return 0;
448
449 unregister_region:
450 unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
451 destroy_class:
452 class_unregister(&telem_class);
453 ida_destroy(&telem_ida);
454 return ret;
455 }
456
telem_module_exit(void)457 static void __exit telem_module_exit(void)
458 {
459 platform_driver_unregister(&telem_driver);
460 unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
461 class_unregister(&telem_class);
462 ida_destroy(&telem_ida);
463 }
464
465 module_init(telem_module_init);
466 module_exit(telem_module_exit);
467
468 MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
469 MODULE_DESCRIPTION("Wilco EC telemetry driver");
470 MODULE_LICENSE("GPL");
471 MODULE_ALIAS("platform:" DRV_NAME);
472