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 	.owner	= THIS_MODULE,
46 	.name	= TELEM_CLASS_NAME,
47 };
48 
49 /* Keep track of all the device numbers used. */
50 #define TELEM_MAX_DEV 128
51 static int telem_major;
52 static DEFINE_IDA(telem_ida);
53 
54 /* EC telemetry command codes */
55 #define WILCO_EC_TELEM_GET_LOG			0x99
56 #define WILCO_EC_TELEM_GET_VERSION		0x38
57 #define WILCO_EC_TELEM_GET_FAN_INFO		0x2E
58 #define WILCO_EC_TELEM_GET_DIAG_INFO		0xFA
59 #define WILCO_EC_TELEM_GET_TEMP_INFO		0x95
60 #define WILCO_EC_TELEM_GET_TEMP_READ		0x2C
61 #define WILCO_EC_TELEM_GET_BATT_EXT_INFO	0x07
62 #define WILCO_EC_TELEM_GET_BATT_PPID_INFO	0x8A
63 
64 #define TELEM_ARGS_SIZE_MAX	30
65 
66 /*
67  * The following telem_args_get_* structs are embedded within the |args| field
68  * of wilco_ec_telem_request.
69  */
70 
71 struct telem_args_get_log {
72 	u8 log_type;
73 	u8 log_index;
74 } __packed;
75 
76 /*
77  * Get a piece of info about the EC firmware version:
78  * 0 = label
79  * 1 = svn_rev
80  * 2 = model_no
81  * 3 = build_date
82  * 4 = frio_version
83  */
84 struct telem_args_get_version {
85 	u8 index;
86 } __packed;
87 
88 struct telem_args_get_fan_info {
89 	u8 command;
90 	u8 fan_number;
91 	u8 arg;
92 } __packed;
93 
94 struct telem_args_get_diag_info {
95 	u8 type;
96 	u8 sub_type;
97 } __packed;
98 
99 struct telem_args_get_temp_info {
100 	u8 command;
101 	u8 index;
102 	u8 field;
103 	u8 zone;
104 } __packed;
105 
106 struct telem_args_get_temp_read {
107 	u8 sensor_index;
108 } __packed;
109 
110 struct telem_args_get_batt_ext_info {
111 	u8 var_args[5];
112 } __packed;
113 
114 struct telem_args_get_batt_ppid_info {
115 	u8 always1; /* Should always be 1 */
116 } __packed;
117 
118 /**
119  * struct wilco_ec_telem_request - Telemetry command and arguments sent to EC.
120  * @command: One of WILCO_EC_TELEM_GET_* command codes.
121  * @reserved: Must be 0.
122  * @args: The first N bytes are one of telem_args_get_* structs, the rest is 0.
123  */
124 struct wilco_ec_telem_request {
125 	u8 command;
126 	u8 reserved;
127 	union {
128 		u8 buf[TELEM_ARGS_SIZE_MAX];
129 		struct telem_args_get_log		get_log;
130 		struct telem_args_get_version		get_version;
131 		struct telem_args_get_fan_info		get_fan_info;
132 		struct telem_args_get_diag_info		get_diag_info;
133 		struct telem_args_get_temp_info		get_temp_info;
134 		struct telem_args_get_temp_read		get_temp_read;
135 		struct telem_args_get_batt_ext_info	get_batt_ext_info;
136 		struct telem_args_get_batt_ppid_info	get_batt_ppid_info;
137 	} args;
138 } __packed;
139 
140 /**
141  * check_telem_request() - Ensure that a request from userspace is valid.
142  * @rq: Request buffer copied from userspace.
143  * @size: Number of bytes copied from userspace.
144  *
145  * Return: 0 if valid, -EINVAL if bad command or reserved byte is non-zero,
146  *         -EMSGSIZE if the request is too long.
147  *
148  * We do not want to allow userspace to send arbitrary telemetry commands to
149  * the EC. Therefore we check to ensure that
150  * 1. The request follows the format of struct wilco_ec_telem_request.
151  * 2. The supplied command code is one of the allowlisted commands.
152  * 3. The request only contains the necessary data for the header and arguments.
153  */
154 static int check_telem_request(struct wilco_ec_telem_request *rq,
155 			       size_t size)
156 {
157 	size_t max_size = offsetof(struct wilco_ec_telem_request, args);
158 
159 	if (rq->reserved)
160 		return -EINVAL;
161 
162 	switch (rq->command) {
163 	case WILCO_EC_TELEM_GET_LOG:
164 		max_size += sizeof(rq->args.get_log);
165 		break;
166 	case WILCO_EC_TELEM_GET_VERSION:
167 		max_size += sizeof(rq->args.get_version);
168 		break;
169 	case WILCO_EC_TELEM_GET_FAN_INFO:
170 		max_size += sizeof(rq->args.get_fan_info);
171 		break;
172 	case WILCO_EC_TELEM_GET_DIAG_INFO:
173 		max_size += sizeof(rq->args.get_diag_info);
174 		break;
175 	case WILCO_EC_TELEM_GET_TEMP_INFO:
176 		max_size += sizeof(rq->args.get_temp_info);
177 		break;
178 	case WILCO_EC_TELEM_GET_TEMP_READ:
179 		max_size += sizeof(rq->args.get_temp_read);
180 		break;
181 	case WILCO_EC_TELEM_GET_BATT_EXT_INFO:
182 		max_size += sizeof(rq->args.get_batt_ext_info);
183 		break;
184 	case WILCO_EC_TELEM_GET_BATT_PPID_INFO:
185 		if (rq->args.get_batt_ppid_info.always1 != 1)
186 			return -EINVAL;
187 
188 		max_size += sizeof(rq->args.get_batt_ppid_info);
189 		break;
190 	default:
191 		return -EINVAL;
192 	}
193 
194 	return (size <= max_size) ? 0 : -EMSGSIZE;
195 }
196 
197 /**
198  * struct telem_device_data - Data for a Wilco EC device that queries telemetry.
199  * @cdev: Char dev that userspace reads and polls from.
200  * @dev: Device associated with the %cdev.
201  * @ec: Wilco EC that we will be communicating with using the mailbox interface.
202  * @available: Boolean of if the device can be opened.
203  */
204 struct telem_device_data {
205 	struct device dev;
206 	struct cdev cdev;
207 	struct wilco_ec_device *ec;
208 	atomic_t available;
209 };
210 
211 #define TELEM_RESPONSE_SIZE	EC_MAILBOX_DATA_SIZE
212 
213 /**
214  * struct telem_session_data - Data that exists between open() and release().
215  * @dev_data: Pointer to get back to the device data and EC.
216  * @request: Command and arguments sent to EC.
217  * @response: Response buffer of data from EC.
218  * @has_msg: Is there data available to read from a previous write?
219  */
220 struct telem_session_data {
221 	struct telem_device_data *dev_data;
222 	struct wilco_ec_telem_request request;
223 	u8 response[TELEM_RESPONSE_SIZE];
224 	bool has_msg;
225 };
226 
227 /**
228  * telem_open() - Callback for when the device node is opened.
229  * @inode: inode for this char device node.
230  * @filp: file for this char device node.
231  *
232  * We need to ensure that after writing a command to the device,
233  * the same userspace process reads the corresponding result.
234  * Therefore, we increment a refcount on opening the device, so that
235  * only one process can communicate with the EC at a time.
236  *
237  * Return: 0 on success, or negative error code on failure.
238  */
239 static int telem_open(struct inode *inode, struct file *filp)
240 {
241 	struct telem_device_data *dev_data;
242 	struct telem_session_data *sess_data;
243 
244 	/* Ensure device isn't already open */
245 	dev_data = container_of(inode->i_cdev, struct telem_device_data, cdev);
246 	if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
247 		return -EBUSY;
248 
249 	get_device(&dev_data->dev);
250 
251 	sess_data = kzalloc(sizeof(*sess_data), GFP_KERNEL);
252 	if (!sess_data) {
253 		atomic_set(&dev_data->available, 1);
254 		return -ENOMEM;
255 	}
256 	sess_data->dev_data = dev_data;
257 	sess_data->has_msg = false;
258 
259 	nonseekable_open(inode, filp);
260 	filp->private_data = sess_data;
261 
262 	return 0;
263 }
264 
265 static ssize_t telem_write(struct file *filp, const char __user *buf,
266 			   size_t count, loff_t *pos)
267 {
268 	struct telem_session_data *sess_data = filp->private_data;
269 	struct wilco_ec_message msg = {};
270 	int ret;
271 
272 	if (count > sizeof(sess_data->request))
273 		return -EMSGSIZE;
274 	memset(&sess_data->request, 0, sizeof(sess_data->request));
275 	if (copy_from_user(&sess_data->request, buf, count))
276 		return -EFAULT;
277 	ret = check_telem_request(&sess_data->request, count);
278 	if (ret < 0)
279 		return ret;
280 
281 	memset(sess_data->response, 0, sizeof(sess_data->response));
282 	msg.type = WILCO_EC_MSG_TELEMETRY;
283 	msg.request_data = &sess_data->request;
284 	msg.request_size = sizeof(sess_data->request);
285 	msg.response_data = sess_data->response;
286 	msg.response_size = sizeof(sess_data->response);
287 
288 	ret = wilco_ec_mailbox(sess_data->dev_data->ec, &msg);
289 	if (ret < 0)
290 		return ret;
291 	if (ret != sizeof(sess_data->response))
292 		return -EMSGSIZE;
293 
294 	sess_data->has_msg = true;
295 
296 	return count;
297 }
298 
299 static ssize_t telem_read(struct file *filp, char __user *buf, size_t count,
300 			  loff_t *pos)
301 {
302 	struct telem_session_data *sess_data = filp->private_data;
303 
304 	if (!sess_data->has_msg)
305 		return -ENODATA;
306 	if (count > sizeof(sess_data->response))
307 		return -EINVAL;
308 
309 	if (copy_to_user(buf, sess_data->response, count))
310 		return -EFAULT;
311 
312 	sess_data->has_msg = false;
313 
314 	return count;
315 }
316 
317 static int telem_release(struct inode *inode, struct file *filp)
318 {
319 	struct telem_session_data *sess_data = filp->private_data;
320 
321 	atomic_set(&sess_data->dev_data->available, 1);
322 	put_device(&sess_data->dev_data->dev);
323 	kfree(sess_data);
324 
325 	return 0;
326 }
327 
328 static const struct file_operations telem_fops = {
329 	.open = telem_open,
330 	.write = telem_write,
331 	.read = telem_read,
332 	.release = telem_release,
333 	.llseek = no_llseek,
334 	.owner = THIS_MODULE,
335 };
336 
337 /**
338  * telem_device_free() - Callback to free the telem_device_data structure.
339  * @d: The device embedded in our device data, which we have been ref counting.
340  *
341  * Once all open file descriptors are closed and the device has been removed,
342  * the refcount of the device will fall to 0 and this will be called.
343  */
344 static void telem_device_free(struct device *d)
345 {
346 	struct telem_device_data *dev_data;
347 
348 	dev_data = container_of(d, struct telem_device_data, dev);
349 	kfree(dev_data);
350 }
351 
352 /**
353  * telem_device_probe() - Callback when creating a new device.
354  * @pdev: platform device that we will be receiving telems from.
355  *
356  * This finds a free minor number for the device, allocates and initializes
357  * some device data, and creates a new device and char dev node.
358  *
359  * Return: 0 on success, negative error code on failure.
360  */
361 static int telem_device_probe(struct platform_device *pdev)
362 {
363 	struct telem_device_data *dev_data;
364 	int error, minor;
365 
366 	/* Get the next available device number */
367 	minor = ida_alloc_max(&telem_ida, TELEM_MAX_DEV-1, GFP_KERNEL);
368 	if (minor < 0) {
369 		error = minor;
370 		dev_err(&pdev->dev, "Failed to find minor number: %d", error);
371 		return error;
372 	}
373 
374 	dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
375 	if (!dev_data) {
376 		ida_simple_remove(&telem_ida, minor);
377 		return -ENOMEM;
378 	}
379 
380 	/* Initialize the device data */
381 	dev_data->ec = dev_get_platdata(&pdev->dev);
382 	atomic_set(&dev_data->available, 1);
383 	platform_set_drvdata(pdev, dev_data);
384 
385 	/* Initialize the device */
386 	dev_data->dev.devt = MKDEV(telem_major, minor);
387 	dev_data->dev.class = &telem_class;
388 	dev_data->dev.release = telem_device_free;
389 	dev_set_name(&dev_data->dev, TELEM_DEV_NAME_FMT, minor);
390 	device_initialize(&dev_data->dev);
391 
392 	/* Initialize the character device and add it to userspace */;
393 	cdev_init(&dev_data->cdev, &telem_fops);
394 	error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
395 	if (error) {
396 		put_device(&dev_data->dev);
397 		ida_simple_remove(&telem_ida, minor);
398 		return error;
399 	}
400 
401 	return 0;
402 }
403 
404 static int telem_device_remove(struct platform_device *pdev)
405 {
406 	struct telem_device_data *dev_data = platform_get_drvdata(pdev);
407 
408 	cdev_device_del(&dev_data->cdev, &dev_data->dev);
409 	ida_simple_remove(&telem_ida, MINOR(dev_data->dev.devt));
410 	put_device(&dev_data->dev);
411 
412 	return 0;
413 }
414 
415 static struct platform_driver telem_driver = {
416 	.probe = telem_device_probe,
417 	.remove = telem_device_remove,
418 	.driver = {
419 		.name = DRV_NAME,
420 	},
421 };
422 
423 static int __init telem_module_init(void)
424 {
425 	dev_t dev_num = 0;
426 	int ret;
427 
428 	ret = class_register(&telem_class);
429 	if (ret) {
430 		pr_err(DRV_NAME ": Failed registering class: %d", ret);
431 		return ret;
432 	}
433 
434 	/* Request the kernel for device numbers, starting with minor=0 */
435 	ret = alloc_chrdev_region(&dev_num, 0, TELEM_MAX_DEV, TELEM_DEV_NAME);
436 	if (ret) {
437 		pr_err(DRV_NAME ": Failed allocating dev numbers: %d", ret);
438 		goto destroy_class;
439 	}
440 	telem_major = MAJOR(dev_num);
441 
442 	ret = platform_driver_register(&telem_driver);
443 	if (ret < 0) {
444 		pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
445 		goto unregister_region;
446 	}
447 
448 	return 0;
449 
450 unregister_region:
451 	unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
452 destroy_class:
453 	class_unregister(&telem_class);
454 	ida_destroy(&telem_ida);
455 	return ret;
456 }
457 
458 static void __exit telem_module_exit(void)
459 {
460 	platform_driver_unregister(&telem_driver);
461 	unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
462 	class_unregister(&telem_class);
463 	ida_destroy(&telem_ida);
464 }
465 
466 module_init(telem_module_init);
467 module_exit(telem_module_exit);
468 
469 MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
470 MODULE_DESCRIPTION("Wilco EC telemetry driver");
471 MODULE_LICENSE("GPL");
472 MODULE_ALIAS("platform:" DRV_NAME);
473