1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * ACPI event handling for Wilco Embedded Controller
4 *
5 * Copyright 2019 Google LLC
6 *
7 * The Wilco Embedded Controller can create custom events that
8 * are not handled as standard ACPI objects. These events can
9 * contain information about changes in EC controlled features,
10 * such as errors and events in the dock or display. For example,
11 * an event is triggered if the dock is plugged into a display
12 * incorrectly. These events are needed for telemetry and
13 * diagnostics reasons, and for possibly alerting the user.
14
15 * These events are triggered by the EC with an ACPI Notify(0x90),
16 * and then the BIOS reads the event buffer from EC RAM via an
17 * ACPI method. When the OS receives these events via ACPI,
18 * it passes them along to this driver. The events are put into
19 * a queue which can be read by a userspace daemon via a char device
20 * that implements read() and poll(). The event queue acts as a
21 * circular buffer of size 64, so if there are no userspace consumers
22 * the kernel will not run out of memory. The char device will appear at
23 * /dev/wilco_event{n}, where n is some small non-negative integer,
24 * starting from 0. Standard ACPI events such as the battery getting
25 * plugged/unplugged can also come through this path, but they are
26 * dealt with via other paths, and are ignored here.
27
28 * To test, you can tail the binary data with
29 * $ cat /dev/wilco_event0 | hexdump -ve '1/1 "%x\n"'
30 * and then create an event by plugging/unplugging the battery.
31 */
32
33 #include <linux/acpi.h>
34 #include <linux/cdev.h>
35 #include <linux/device.h>
36 #include <linux/fs.h>
37 #include <linux/idr.h>
38 #include <linux/io.h>
39 #include <linux/list.h>
40 #include <linux/module.h>
41 #include <linux/poll.h>
42 #include <linux/spinlock.h>
43 #include <linux/uaccess.h>
44 #include <linux/wait.h>
45
46 /* ACPI Notify event code indicating event data is available. */
47 #define EC_ACPI_NOTIFY_EVENT 0x90
48 /* ACPI Method to execute to retrieve event data buffer from the EC. */
49 #define EC_ACPI_GET_EVENT "QSET"
50 /* Maximum number of words in event data returned by the EC. */
51 #define EC_ACPI_MAX_EVENT_WORDS 6
52 #define EC_ACPI_MAX_EVENT_SIZE \
53 (sizeof(struct ec_event) + (EC_ACPI_MAX_EVENT_WORDS) * sizeof(u16))
54
55 /* Node will appear in /dev/EVENT_DEV_NAME */
56 #define EVENT_DEV_NAME "wilco_event"
57 #define EVENT_CLASS_NAME EVENT_DEV_NAME
58 #define DRV_NAME EVENT_DEV_NAME
59 #define EVENT_DEV_NAME_FMT (EVENT_DEV_NAME "%d")
60 static struct class event_class = {
61 .name = EVENT_CLASS_NAME,
62 };
63
64 /* Keep track of all the device numbers used. */
65 #define EVENT_MAX_DEV 128
66 static int event_major;
67 static DEFINE_IDA(event_ida);
68
69 /* Size of circular queue of events. */
70 #define MAX_NUM_EVENTS 64
71
72 /**
73 * struct ec_event - Extended event returned by the EC.
74 * @size: Number of 16bit words in structure after the size word.
75 * @type: Extended event type, meaningless for us.
76 * @event: Event data words. Max count is %EC_ACPI_MAX_EVENT_WORDS.
77 */
78 struct ec_event {
79 u16 size;
80 u16 type;
81 u16 event[];
82 } __packed;
83
84 #define ec_event_num_words(ev) (ev->size - 1)
85 #define ec_event_size(ev) (sizeof(*ev) + (ec_event_num_words(ev) * sizeof(u16)))
86
87 /**
88 * struct ec_event_queue - Circular queue for events.
89 * @capacity: Number of elements the queue can hold.
90 * @head: Next index to write to.
91 * @tail: Next index to read from.
92 * @entries: Array of events.
93 */
94 struct ec_event_queue {
95 int capacity;
96 int head;
97 int tail;
98 struct ec_event *entries[] __counted_by(capacity);
99 };
100
101 /* Maximum number of events to store in ec_event_queue */
102 static int queue_size = 64;
103 module_param(queue_size, int, 0644);
104
event_queue_new(int capacity)105 static struct ec_event_queue *event_queue_new(int capacity)
106 {
107 struct ec_event_queue *q;
108
109 q = kzalloc(struct_size(q, entries, capacity), GFP_KERNEL);
110 if (!q)
111 return NULL;
112
113 q->capacity = capacity;
114
115 return q;
116 }
117
event_queue_empty(struct ec_event_queue * q)118 static inline bool event_queue_empty(struct ec_event_queue *q)
119 {
120 /* head==tail when both full and empty, but head==NULL when empty */
121 return q->head == q->tail && !q->entries[q->head];
122 }
123
event_queue_full(struct ec_event_queue * q)124 static inline bool event_queue_full(struct ec_event_queue *q)
125 {
126 /* head==tail when both full and empty, but head!=NULL when full */
127 return q->head == q->tail && q->entries[q->head];
128 }
129
event_queue_pop(struct ec_event_queue * q)130 static struct ec_event *event_queue_pop(struct ec_event_queue *q)
131 {
132 struct ec_event *ev;
133
134 if (event_queue_empty(q))
135 return NULL;
136
137 ev = q->entries[q->tail];
138 q->entries[q->tail] = NULL;
139 q->tail = (q->tail + 1) % q->capacity;
140
141 return ev;
142 }
143
144 /*
145 * If full, overwrite the oldest event and return it so the caller
146 * can kfree it. If not full, return NULL.
147 */
event_queue_push(struct ec_event_queue * q,struct ec_event * ev)148 static struct ec_event *event_queue_push(struct ec_event_queue *q,
149 struct ec_event *ev)
150 {
151 struct ec_event *popped = NULL;
152
153 if (event_queue_full(q))
154 popped = event_queue_pop(q);
155 q->entries[q->head] = ev;
156 q->head = (q->head + 1) % q->capacity;
157
158 return popped;
159 }
160
event_queue_free(struct ec_event_queue * q)161 static void event_queue_free(struct ec_event_queue *q)
162 {
163 struct ec_event *event;
164
165 while ((event = event_queue_pop(q)) != NULL)
166 kfree(event);
167
168 kfree(q);
169 }
170
171 /**
172 * struct event_device_data - Data for a Wilco EC device that responds to ACPI.
173 * @events: Circular queue of EC events to be provided to userspace.
174 * @queue_lock: Protect the queue from simultaneous read/writes.
175 * @wq: Wait queue to notify processes when events are available or the
176 * device has been removed.
177 * @cdev: Char dev that userspace reads() and polls() from.
178 * @dev: Device associated with the %cdev.
179 * @exist: Has the device been not been removed? Once a device has been removed,
180 * writes, reads, and new opens will fail.
181 * @available: Guarantee only one client can open() file and read from queue.
182 *
183 * There will be one of these structs for each ACPI device registered. This data
184 * is the queue of events received from ACPI that still need to be read from
185 * userspace, the device and char device that userspace is using, a wait queue
186 * used to notify different threads when something has changed, plus a flag
187 * on whether the ACPI device has been removed.
188 */
189 struct event_device_data {
190 struct ec_event_queue *events;
191 spinlock_t queue_lock;
192 wait_queue_head_t wq;
193 struct device dev;
194 struct cdev cdev;
195 bool exist;
196 atomic_t available;
197 };
198
199 /**
200 * enqueue_events() - Place EC events in queue to be read by userspace.
201 * @adev: Device the events came from.
202 * @buf: Buffer of event data.
203 * @length: Length of event data buffer.
204 *
205 * %buf contains a number of ec_event's, packed one after the other.
206 * Each ec_event is of variable length. Start with the first event, copy it
207 * into a persistent ec_event, store that entry in the queue, move on
208 * to the next ec_event in buf, and repeat.
209 *
210 * Return: 0 on success or negative error code on failure.
211 */
enqueue_events(struct acpi_device * adev,const u8 * buf,u32 length)212 static int enqueue_events(struct acpi_device *adev, const u8 *buf, u32 length)
213 {
214 struct event_device_data *dev_data = adev->driver_data;
215 struct ec_event *event, *queue_event, *old_event;
216 size_t num_words, event_size;
217 u32 offset = 0;
218
219 while (offset < length) {
220 event = (struct ec_event *)(buf + offset);
221
222 num_words = ec_event_num_words(event);
223 event_size = ec_event_size(event);
224 if (num_words > EC_ACPI_MAX_EVENT_WORDS) {
225 dev_err(&adev->dev, "Too many event words: %zu > %d\n",
226 num_words, EC_ACPI_MAX_EVENT_WORDS);
227 return -EOVERFLOW;
228 }
229
230 /* Ensure event does not overflow the available buffer */
231 if ((offset + event_size) > length) {
232 dev_err(&adev->dev, "Event exceeds buffer: %zu > %d\n",
233 offset + event_size, length);
234 return -EOVERFLOW;
235 }
236
237 /* Point to the next event in the buffer */
238 offset += event_size;
239
240 /* Copy event into the queue */
241 queue_event = kmemdup(event, event_size, GFP_KERNEL);
242 if (!queue_event)
243 return -ENOMEM;
244 spin_lock(&dev_data->queue_lock);
245 old_event = event_queue_push(dev_data->events, queue_event);
246 spin_unlock(&dev_data->queue_lock);
247 kfree(old_event);
248 wake_up_interruptible(&dev_data->wq);
249 }
250
251 return 0;
252 }
253
254 /**
255 * event_device_notify() - Callback when EC generates an event over ACPI.
256 * @adev: The device that the event is coming from.
257 * @value: Value passed to Notify() in ACPI.
258 *
259 * This function will read the events from the device and enqueue them.
260 */
event_device_notify(struct acpi_device * adev,u32 value)261 static void event_device_notify(struct acpi_device *adev, u32 value)
262 {
263 struct acpi_buffer event_buffer = { ACPI_ALLOCATE_BUFFER, NULL };
264 union acpi_object *obj;
265 acpi_status status;
266
267 if (value != EC_ACPI_NOTIFY_EVENT) {
268 dev_err(&adev->dev, "Invalid event: 0x%08x\n", value);
269 return;
270 }
271
272 /* Execute ACPI method to get event data buffer. */
273 status = acpi_evaluate_object(adev->handle, EC_ACPI_GET_EVENT,
274 NULL, &event_buffer);
275 if (ACPI_FAILURE(status)) {
276 dev_err(&adev->dev, "Error executing ACPI method %s()\n",
277 EC_ACPI_GET_EVENT);
278 return;
279 }
280
281 obj = (union acpi_object *)event_buffer.pointer;
282 if (!obj) {
283 dev_err(&adev->dev, "Nothing returned from %s()\n",
284 EC_ACPI_GET_EVENT);
285 return;
286 }
287 if (obj->type != ACPI_TYPE_BUFFER) {
288 dev_err(&adev->dev, "Invalid object returned from %s()\n",
289 EC_ACPI_GET_EVENT);
290 kfree(obj);
291 return;
292 }
293 if (obj->buffer.length < sizeof(struct ec_event)) {
294 dev_err(&adev->dev, "Invalid buffer length %d from %s()\n",
295 obj->buffer.length, EC_ACPI_GET_EVENT);
296 kfree(obj);
297 return;
298 }
299
300 enqueue_events(adev, obj->buffer.pointer, obj->buffer.length);
301 kfree(obj);
302 }
303
event_open(struct inode * inode,struct file * filp)304 static int event_open(struct inode *inode, struct file *filp)
305 {
306 struct event_device_data *dev_data;
307
308 dev_data = container_of(inode->i_cdev, struct event_device_data, cdev);
309 if (!dev_data->exist)
310 return -ENODEV;
311
312 if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
313 return -EBUSY;
314
315 /* Increase refcount on device so dev_data is not freed */
316 get_device(&dev_data->dev);
317 stream_open(inode, filp);
318 filp->private_data = dev_data;
319
320 return 0;
321 }
322
event_poll(struct file * filp,poll_table * wait)323 static __poll_t event_poll(struct file *filp, poll_table *wait)
324 {
325 struct event_device_data *dev_data = filp->private_data;
326 __poll_t mask = 0;
327
328 poll_wait(filp, &dev_data->wq, wait);
329 if (!dev_data->exist)
330 return EPOLLHUP;
331 if (!event_queue_empty(dev_data->events))
332 mask |= EPOLLIN | EPOLLRDNORM | EPOLLPRI;
333 return mask;
334 }
335
336 /**
337 * event_read() - Callback for passing event data to userspace via read().
338 * @filp: The file we are reading from.
339 * @buf: Pointer to userspace buffer to fill with one event.
340 * @count: Number of bytes requested. Must be at least EC_ACPI_MAX_EVENT_SIZE.
341 * @pos: File position pointer, irrelevant since we don't support seeking.
342 *
343 * Removes the first event from the queue, places it in the passed buffer.
344 *
345 * If there are no events in the queue, then one of two things happens,
346 * depending on if the file was opened in nonblocking mode: If in nonblocking
347 * mode, then return -EAGAIN to say there's no data. If in blocking mode, then
348 * block until an event is available.
349 *
350 * Return: Number of bytes placed in buffer, negative error code on failure.
351 */
event_read(struct file * filp,char __user * buf,size_t count,loff_t * pos)352 static ssize_t event_read(struct file *filp, char __user *buf, size_t count,
353 loff_t *pos)
354 {
355 struct event_device_data *dev_data = filp->private_data;
356 struct ec_event *event;
357 ssize_t n_bytes_written = 0;
358 int err;
359
360 /* We only will give them the entire event at once */
361 if (count != 0 && count < EC_ACPI_MAX_EVENT_SIZE)
362 return -EINVAL;
363
364 spin_lock(&dev_data->queue_lock);
365 while (event_queue_empty(dev_data->events)) {
366 spin_unlock(&dev_data->queue_lock);
367 if (filp->f_flags & O_NONBLOCK)
368 return -EAGAIN;
369
370 err = wait_event_interruptible(dev_data->wq,
371 !event_queue_empty(dev_data->events) ||
372 !dev_data->exist);
373 if (err)
374 return err;
375
376 /* Device was removed as we waited? */
377 if (!dev_data->exist)
378 return -ENODEV;
379 spin_lock(&dev_data->queue_lock);
380 }
381 event = event_queue_pop(dev_data->events);
382 spin_unlock(&dev_data->queue_lock);
383 n_bytes_written = ec_event_size(event);
384 if (copy_to_user(buf, event, n_bytes_written))
385 n_bytes_written = -EFAULT;
386 kfree(event);
387
388 return n_bytes_written;
389 }
390
event_release(struct inode * inode,struct file * filp)391 static int event_release(struct inode *inode, struct file *filp)
392 {
393 struct event_device_data *dev_data = filp->private_data;
394
395 atomic_set(&dev_data->available, 1);
396 put_device(&dev_data->dev);
397
398 return 0;
399 }
400
401 static const struct file_operations event_fops = {
402 .open = event_open,
403 .poll = event_poll,
404 .read = event_read,
405 .release = event_release,
406 .owner = THIS_MODULE,
407 };
408
409 /**
410 * free_device_data() - Callback to free the event_device_data structure.
411 * @d: The device embedded in our device data, which we have been ref counting.
412 *
413 * This is called only after event_device_remove() has been called and all
414 * userspace programs have called event_release() on all the open file
415 * descriptors.
416 */
free_device_data(struct device * d)417 static void free_device_data(struct device *d)
418 {
419 struct event_device_data *dev_data;
420
421 dev_data = container_of(d, struct event_device_data, dev);
422 event_queue_free(dev_data->events);
423 kfree(dev_data);
424 }
425
hangup_device(struct event_device_data * dev_data)426 static void hangup_device(struct event_device_data *dev_data)
427 {
428 dev_data->exist = false;
429 /* Wake up the waiting processes so they can close. */
430 wake_up_interruptible(&dev_data->wq);
431 put_device(&dev_data->dev);
432 }
433
434 /**
435 * event_device_add() - Callback when creating a new device.
436 * @adev: ACPI device that we will be receiving events from.
437 *
438 * This finds a free minor number for the device, allocates and initializes
439 * some device data, and creates a new device and char dev node.
440 *
441 * The device data is freed in free_device_data(), which is called when
442 * %dev_data->dev is release()ed. This happens after all references to
443 * %dev_data->dev are dropped, which happens once both event_device_remove()
444 * has been called and every open()ed file descriptor has been release()ed.
445 *
446 * Return: 0 on success, negative error code on failure.
447 */
event_device_add(struct acpi_device * adev)448 static int event_device_add(struct acpi_device *adev)
449 {
450 struct event_device_data *dev_data;
451 int error, minor;
452
453 minor = ida_alloc_max(&event_ida, EVENT_MAX_DEV-1, GFP_KERNEL);
454 if (minor < 0) {
455 error = minor;
456 dev_err(&adev->dev, "Failed to find minor number: %d\n", error);
457 return error;
458 }
459
460 dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
461 if (!dev_data) {
462 error = -ENOMEM;
463 goto free_minor;
464 }
465
466 /* Initialize the device data. */
467 adev->driver_data = dev_data;
468 dev_data->events = event_queue_new(queue_size);
469 if (!dev_data->events) {
470 kfree(dev_data);
471 error = -ENOMEM;
472 goto free_minor;
473 }
474 spin_lock_init(&dev_data->queue_lock);
475 init_waitqueue_head(&dev_data->wq);
476 dev_data->exist = true;
477 atomic_set(&dev_data->available, 1);
478
479 /* Initialize the device. */
480 dev_data->dev.devt = MKDEV(event_major, minor);
481 dev_data->dev.class = &event_class;
482 dev_data->dev.release = free_device_data;
483 dev_set_name(&dev_data->dev, EVENT_DEV_NAME_FMT, minor);
484 device_initialize(&dev_data->dev);
485
486 /* Initialize the character device, and add it to userspace. */
487 cdev_init(&dev_data->cdev, &event_fops);
488 error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
489 if (error)
490 goto free_dev_data;
491
492 return 0;
493
494 free_dev_data:
495 hangup_device(dev_data);
496 free_minor:
497 ida_free(&event_ida, minor);
498 return error;
499 }
500
event_device_remove(struct acpi_device * adev)501 static void event_device_remove(struct acpi_device *adev)
502 {
503 struct event_device_data *dev_data = adev->driver_data;
504
505 cdev_device_del(&dev_data->cdev, &dev_data->dev);
506 ida_free(&event_ida, MINOR(dev_data->dev.devt));
507 hangup_device(dev_data);
508 }
509
510 static const struct acpi_device_id event_acpi_ids[] = {
511 { "GOOG000D", 0 },
512 { }
513 };
514 MODULE_DEVICE_TABLE(acpi, event_acpi_ids);
515
516 static struct acpi_driver event_driver = {
517 .name = DRV_NAME,
518 .class = DRV_NAME,
519 .ids = event_acpi_ids,
520 .ops = {
521 .add = event_device_add,
522 .notify = event_device_notify,
523 .remove = event_device_remove,
524 },
525 };
526
event_module_init(void)527 static int __init event_module_init(void)
528 {
529 dev_t dev_num = 0;
530 int ret;
531
532 ret = class_register(&event_class);
533 if (ret) {
534 pr_err(DRV_NAME ": Failed registering class: %d\n", ret);
535 return ret;
536 }
537
538 /* Request device numbers, starting with minor=0. Save the major num. */
539 ret = alloc_chrdev_region(&dev_num, 0, EVENT_MAX_DEV, EVENT_DEV_NAME);
540 if (ret) {
541 pr_err(DRV_NAME ": Failed allocating dev numbers: %d\n", ret);
542 goto destroy_class;
543 }
544 event_major = MAJOR(dev_num);
545
546 ret = acpi_bus_register_driver(&event_driver);
547 if (ret < 0) {
548 pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
549 goto unregister_region;
550 }
551
552 return 0;
553
554 unregister_region:
555 unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
556 destroy_class:
557 class_unregister(&event_class);
558 ida_destroy(&event_ida);
559 return ret;
560 }
561
event_module_exit(void)562 static void __exit event_module_exit(void)
563 {
564 acpi_bus_unregister_driver(&event_driver);
565 unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
566 class_unregister(&event_class);
567 ida_destroy(&event_ida);
568 }
569
570 module_init(event_module_init);
571 module_exit(event_module_exit);
572
573 MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
574 MODULE_DESCRIPTION("Wilco EC ACPI event driver");
575 MODULE_LICENSE("GPL");
576