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")
44static 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
50static int telem_major;
51static 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
70struct 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 */
83struct telem_args_get_version {
84	u8 index;
85} __packed;
86
87struct telem_args_get_fan_info {
88	u8 command;
89	u8 fan_number;
90	u8 arg;
91} __packed;
92
93struct telem_args_get_diag_info {
94	u8 type;
95	u8 sub_type;
96} __packed;
97
98struct telem_args_get_temp_info {
99	u8 command;
100	u8 index;
101	u8 field;
102	u8 zone;
103} __packed;
104
105struct telem_args_get_temp_read {
106	u8 sensor_index;
107} __packed;
108
109struct telem_args_get_batt_ext_info {
110	u8 var_args[5];
111} __packed;
112
113struct 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 */
123struct 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 */
153static 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 */
203struct 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 */
219struct 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 */
238static 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
264static 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
298static 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
316static 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
327static 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 */
343static 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 */
360static 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_free(&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_free(&telem_ida, minor);
397		return error;
398	}
399
400	return 0;
401}
402
403static void 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_free(&telem_ida, MINOR(dev_data->dev.devt));
409	put_device(&dev_data->dev);
410}
411
412static struct platform_driver telem_driver = {
413	.probe = telem_device_probe,
414	.remove_new = telem_device_remove,
415	.driver = {
416		.name = DRV_NAME,
417	},
418};
419
420static int __init telem_module_init(void)
421{
422	dev_t dev_num = 0;
423	int ret;
424
425	ret = class_register(&telem_class);
426	if (ret) {
427		pr_err(DRV_NAME ": Failed registering class: %d\n", ret);
428		return ret;
429	}
430
431	/* Request the kernel for device numbers, starting with minor=0 */
432	ret = alloc_chrdev_region(&dev_num, 0, TELEM_MAX_DEV, TELEM_DEV_NAME);
433	if (ret) {
434		pr_err(DRV_NAME ": Failed allocating dev numbers: %d\n", ret);
435		goto destroy_class;
436	}
437	telem_major = MAJOR(dev_num);
438
439	ret = platform_driver_register(&telem_driver);
440	if (ret < 0) {
441		pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
442		goto unregister_region;
443	}
444
445	return 0;
446
447unregister_region:
448	unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
449destroy_class:
450	class_unregister(&telem_class);
451	ida_destroy(&telem_ida);
452	return ret;
453}
454
455static void __exit telem_module_exit(void)
456{
457	platform_driver_unregister(&telem_driver);
458	unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
459	class_unregister(&telem_class);
460	ida_destroy(&telem_ida);
461}
462
463module_init(telem_module_init);
464module_exit(telem_module_exit);
465
466MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
467MODULE_DESCRIPTION("Wilco EC telemetry driver");
468MODULE_LICENSE("GPL");
469MODULE_ALIAS("platform:" DRV_NAME);
470