1 // SPDX-License-Identifier: GPL-2.0
3 * Telemetry communication for Wilco EC
5 * Copyright 2019 Google LLC
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.
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.
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
30 #include <linux/cdev.h>
31 #include <linux/device.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>
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 = {
46 .name = TELEM_CLASS_NAME,
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);
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
64 #define TELEM_ARGS_SIZE_MAX 30
67 * The following telem_args_get_* structs are embedded within the |args| field
68 * of wilco_ec_telem_request.
71 struct telem_args_get_log {
77 * Get a piece of info about the EC firmware version:
84 struct telem_args_get_version {
88 struct telem_args_get_fan_info {
94 struct telem_args_get_diag_info {
99 struct telem_args_get_temp_info {
106 struct telem_args_get_temp_read {
110 struct telem_args_get_batt_ext_info {
114 struct telem_args_get_batt_ppid_info {
115 u8 always1; /* Should always be 1 */
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.
124 struct wilco_ec_telem_request {
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;
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.
145 * Return: 0 if valid, -EINVAL if bad command or reserved byte is non-zero,
146 * -EMSGSIZE if the request is too long.
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.
154 static int check_telem_request(struct wilco_ec_telem_request *rq,
157 size_t max_size = offsetof(struct wilco_ec_telem_request, args);
162 switch (rq->command) {
163 case WILCO_EC_TELEM_GET_LOG:
164 max_size += sizeof(rq->args.get_log);
166 case WILCO_EC_TELEM_GET_VERSION:
167 max_size += sizeof(rq->args.get_version);
169 case WILCO_EC_TELEM_GET_FAN_INFO:
170 max_size += sizeof(rq->args.get_fan_info);
172 case WILCO_EC_TELEM_GET_DIAG_INFO:
173 max_size += sizeof(rq->args.get_diag_info);
175 case WILCO_EC_TELEM_GET_TEMP_INFO:
176 max_size += sizeof(rq->args.get_temp_info);
178 case WILCO_EC_TELEM_GET_TEMP_READ:
179 max_size += sizeof(rq->args.get_temp_read);
181 case WILCO_EC_TELEM_GET_BATT_EXT_INFO:
182 max_size += sizeof(rq->args.get_batt_ext_info);
184 case WILCO_EC_TELEM_GET_BATT_PPID_INFO:
185 if (rq->args.get_batt_ppid_info.always1 != 1)
188 max_size += sizeof(rq->args.get_batt_ppid_info);
194 return (size <= max_size) ? 0 : -EMSGSIZE;
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.
204 struct telem_device_data {
207 struct wilco_ec_device *ec;
211 #define TELEM_RESPONSE_SIZE EC_MAILBOX_DATA_SIZE
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?
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];
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.
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.
237 * Return: 0 on success, or negative error code on failure.
239 static int telem_open(struct inode *inode, struct file *filp)
241 struct telem_device_data *dev_data;
242 struct telem_session_data *sess_data;
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)
249 get_device(&dev_data->dev);
251 sess_data = kzalloc(sizeof(*sess_data), GFP_KERNEL);
253 atomic_set(&dev_data->available, 1);
256 sess_data->dev_data = dev_data;
257 sess_data->has_msg = false;
259 stream_open(inode, filp);
260 filp->private_data = sess_data;
265 static ssize_t telem_write(struct file *filp, const char __user *buf,
266 size_t count, loff_t *pos)
268 struct telem_session_data *sess_data = filp->private_data;
269 struct wilco_ec_message msg = {};
272 if (count > sizeof(sess_data->request))
274 memset(&sess_data->request, 0, sizeof(sess_data->request));
275 if (copy_from_user(&sess_data->request, buf, count))
277 ret = check_telem_request(&sess_data->request, count);
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);
288 ret = wilco_ec_mailbox(sess_data->dev_data->ec, &msg);
291 if (ret != sizeof(sess_data->response))
294 sess_data->has_msg = true;
299 static ssize_t telem_read(struct file *filp, char __user *buf, size_t count,
302 struct telem_session_data *sess_data = filp->private_data;
304 if (!sess_data->has_msg)
306 if (count > sizeof(sess_data->response))
309 if (copy_to_user(buf, sess_data->response, count))
312 sess_data->has_msg = false;
317 static int telem_release(struct inode *inode, struct file *filp)
319 struct telem_session_data *sess_data = filp->private_data;
321 atomic_set(&sess_data->dev_data->available, 1);
322 put_device(&sess_data->dev_data->dev);
328 static const struct file_operations telem_fops = {
330 .write = telem_write,
332 .release = telem_release,
334 .owner = THIS_MODULE,
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.
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.
344 static void telem_device_free(struct device *d)
346 struct telem_device_data *dev_data;
348 dev_data = container_of(d, struct telem_device_data, dev);
353 * telem_device_probe() - Callback when creating a new device.
354 * @pdev: platform device that we will be receiving telems from.
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.
359 * Return: 0 on success, negative error code on failure.
361 static int telem_device_probe(struct platform_device *pdev)
363 struct telem_device_data *dev_data;
366 /* Get the next available device number */
367 minor = ida_alloc_max(&telem_ida, TELEM_MAX_DEV-1, GFP_KERNEL);
370 dev_err(&pdev->dev, "Failed to find minor number: %d\n", error);
374 dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
376 ida_simple_remove(&telem_ida, minor);
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);
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);
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);
396 put_device(&dev_data->dev);
397 ida_simple_remove(&telem_ida, minor);
404 static int telem_device_remove(struct platform_device *pdev)
406 struct telem_device_data *dev_data = platform_get_drvdata(pdev);
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);
415 static struct platform_driver telem_driver = {
416 .probe = telem_device_probe,
417 .remove = telem_device_remove,
423 static int __init telem_module_init(void)
428 ret = class_register(&telem_class);
430 pr_err(DRV_NAME ": Failed registering class: %d\n", ret);
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);
437 pr_err(DRV_NAME ": Failed allocating dev numbers: %d\n", ret);
440 telem_major = MAJOR(dev_num);
442 ret = platform_driver_register(&telem_driver);
444 pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
445 goto unregister_region;
451 unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
453 class_unregister(&telem_class);
454 ida_destroy(&telem_ida);
458 static void __exit telem_module_exit(void)
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);
466 module_init(telem_module_init);
467 module_exit(telem_module_exit);
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);