1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Virtio Transport driver for Arm System Control and Management Interface
4 * (SCMI).
5 *
6 * Copyright (C) 2020-2022 OpenSynergy.
7 * Copyright (C) 2021-2024 ARM Ltd.
8 */
9
10 /**
11 * DOC: Theory of Operation
12 *
13 * The scmi-virtio transport implements a driver for the virtio SCMI device.
14 *
15 * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
16 * channel (virtio eventq, P2A channel). Each channel is implemented through a
17 * virtqueue. Access to each virtqueue is protected by spinlocks.
18 */
19
20 #include <linux/completion.h>
21 #include <linux/errno.h>
22 #include <linux/platform_device.h>
23 #include <linux/refcount.h>
24 #include <linux/slab.h>
25 #include <linux/virtio.h>
26 #include <linux/virtio_config.h>
27
28 #include <uapi/linux/virtio_ids.h>
29 #include <uapi/linux/virtio_scmi.h>
30
31 #include "../common.h"
32
33 #define VIRTIO_MAX_RX_TIMEOUT_MS 60000
34 #define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
35 #define VIRTIO_SCMI_MAX_PDU_SIZE \
36 (VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
37 #define DESCRIPTORS_PER_TX_MSG 2
38
39 /**
40 * struct scmi_vio_channel - Transport channel information
41 *
42 * @vqueue: Associated virtqueue
43 * @cinfo: SCMI Tx or Rx channel
44 * @free_lock: Protects access to the @free_list.
45 * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
46 * @deferred_tx_work: Worker for TX deferred replies processing
47 * @deferred_tx_wq: Workqueue for TX deferred replies
48 * @pending_lock: Protects access to the @pending_cmds_list.
49 * @pending_cmds_list: List of pre-fetched commands queueud for later processing
50 * @is_rx: Whether channel is an Rx channel
51 * @max_msg: Maximum number of pending messages for this channel.
52 * @lock: Protects access to all members except users, free_list and
53 * pending_cmds_list.
54 * @shutdown_done: A reference to a completion used when freeing this channel.
55 * @users: A reference count to currently active users of this channel.
56 */
57 struct scmi_vio_channel {
58 struct virtqueue *vqueue;
59 struct scmi_chan_info *cinfo;
60 /* lock to protect access to the free list. */
61 spinlock_t free_lock;
62 struct list_head free_list;
63 /* lock to protect access to the pending list. */
64 spinlock_t pending_lock;
65 struct list_head pending_cmds_list;
66 struct work_struct deferred_tx_work;
67 struct workqueue_struct *deferred_tx_wq;
68 bool is_rx;
69 unsigned int max_msg;
70 /*
71 * Lock to protect access to all members except users, free_list and
72 * pending_cmds_list
73 */
74 spinlock_t lock;
75 struct completion *shutdown_done;
76 refcount_t users;
77 };
78
79 enum poll_states {
80 VIO_MSG_NOT_POLLED,
81 VIO_MSG_POLL_TIMEOUT,
82 VIO_MSG_POLLING,
83 VIO_MSG_POLL_DONE,
84 };
85
86 /**
87 * struct scmi_vio_msg - Transport PDU information
88 *
89 * @request: SDU used for commands
90 * @input: SDU used for (delayed) responses and notifications
91 * @list: List which scmi_vio_msg may be part of
92 * @rx_len: Input SDU size in bytes, once input has been received
93 * @poll_idx: Last used index registered for polling purposes if this message
94 * transaction reply was configured for polling.
95 * @poll_status: Polling state for this message.
96 * @poll_lock: A lock to protect @poll_status
97 * @users: A reference count to track this message users and avoid premature
98 * freeing (and reuse) when polling and IRQ execution paths interleave.
99 */
100 struct scmi_vio_msg {
101 struct scmi_msg_payld *request;
102 struct scmi_msg_payld *input;
103 struct list_head list;
104 unsigned int rx_len;
105 unsigned int poll_idx;
106 enum poll_states poll_status;
107 /* Lock to protect access to poll_status */
108 spinlock_t poll_lock;
109 refcount_t users;
110 };
111
112 static struct scmi_transport_core_operations *core;
113
114 /* Only one SCMI VirtIO device can possibly exist */
115 static struct virtio_device *scmi_vdev;
116
scmi_vio_channel_ready(struct scmi_vio_channel * vioch,struct scmi_chan_info * cinfo)117 static void scmi_vio_channel_ready(struct scmi_vio_channel *vioch,
118 struct scmi_chan_info *cinfo)
119 {
120 unsigned long flags;
121
122 spin_lock_irqsave(&vioch->lock, flags);
123 cinfo->transport_info = vioch;
124 /* Indirectly setting channel not available any more */
125 vioch->cinfo = cinfo;
126 spin_unlock_irqrestore(&vioch->lock, flags);
127
128 refcount_set(&vioch->users, 1);
129 }
130
scmi_vio_channel_acquire(struct scmi_vio_channel * vioch)131 static inline bool scmi_vio_channel_acquire(struct scmi_vio_channel *vioch)
132 {
133 return refcount_inc_not_zero(&vioch->users);
134 }
135
scmi_vio_channel_release(struct scmi_vio_channel * vioch)136 static inline void scmi_vio_channel_release(struct scmi_vio_channel *vioch)
137 {
138 if (refcount_dec_and_test(&vioch->users)) {
139 unsigned long flags;
140
141 spin_lock_irqsave(&vioch->lock, flags);
142 if (vioch->shutdown_done) {
143 vioch->cinfo = NULL;
144 complete(vioch->shutdown_done);
145 }
146 spin_unlock_irqrestore(&vioch->lock, flags);
147 }
148 }
149
scmi_vio_channel_cleanup_sync(struct scmi_vio_channel * vioch)150 static void scmi_vio_channel_cleanup_sync(struct scmi_vio_channel *vioch)
151 {
152 unsigned long flags;
153 DECLARE_COMPLETION_ONSTACK(vioch_shutdown_done);
154
155 /*
156 * Prepare to wait for the last release if not already released
157 * or in progress.
158 */
159 spin_lock_irqsave(&vioch->lock, flags);
160 if (!vioch->cinfo || vioch->shutdown_done) {
161 spin_unlock_irqrestore(&vioch->lock, flags);
162 return;
163 }
164
165 vioch->shutdown_done = &vioch_shutdown_done;
166 if (!vioch->is_rx && vioch->deferred_tx_wq)
167 /* Cannot be kicked anymore after this...*/
168 vioch->deferred_tx_wq = NULL;
169 spin_unlock_irqrestore(&vioch->lock, flags);
170
171 scmi_vio_channel_release(vioch);
172
173 /* Let any possibly concurrent RX path release the channel */
174 wait_for_completion(vioch->shutdown_done);
175 }
176
177 /* Assumes to be called with vio channel acquired already */
178 static struct scmi_vio_msg *
scmi_virtio_get_free_msg(struct scmi_vio_channel * vioch)179 scmi_virtio_get_free_msg(struct scmi_vio_channel *vioch)
180 {
181 unsigned long flags;
182 struct scmi_vio_msg *msg;
183
184 spin_lock_irqsave(&vioch->free_lock, flags);
185 if (list_empty(&vioch->free_list)) {
186 spin_unlock_irqrestore(&vioch->free_lock, flags);
187 return NULL;
188 }
189
190 msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
191 list_del_init(&msg->list);
192 spin_unlock_irqrestore(&vioch->free_lock, flags);
193
194 /* Still no users, no need to acquire poll_lock */
195 msg->poll_status = VIO_MSG_NOT_POLLED;
196 refcount_set(&msg->users, 1);
197
198 return msg;
199 }
200
scmi_vio_msg_acquire(struct scmi_vio_msg * msg)201 static inline bool scmi_vio_msg_acquire(struct scmi_vio_msg *msg)
202 {
203 return refcount_inc_not_zero(&msg->users);
204 }
205
206 /* Assumes to be called with vio channel acquired already */
scmi_vio_msg_release(struct scmi_vio_channel * vioch,struct scmi_vio_msg * msg)207 static inline bool scmi_vio_msg_release(struct scmi_vio_channel *vioch,
208 struct scmi_vio_msg *msg)
209 {
210 bool ret;
211
212 ret = refcount_dec_and_test(&msg->users);
213 if (ret) {
214 unsigned long flags;
215
216 spin_lock_irqsave(&vioch->free_lock, flags);
217 list_add_tail(&msg->list, &vioch->free_list);
218 spin_unlock_irqrestore(&vioch->free_lock, flags);
219 }
220
221 return ret;
222 }
223
scmi_vio_have_vq_rx(struct virtio_device * vdev)224 static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
225 {
226 return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
227 }
228
scmi_vio_feed_vq_rx(struct scmi_vio_channel * vioch,struct scmi_vio_msg * msg)229 static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
230 struct scmi_vio_msg *msg)
231 {
232 struct scatterlist sg_in;
233 int rc;
234 unsigned long flags;
235 struct device *dev = &vioch->vqueue->vdev->dev;
236
237 sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
238
239 spin_lock_irqsave(&vioch->lock, flags);
240
241 rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
242 if (rc)
243 dev_err(dev, "failed to add to RX virtqueue (%d)\n", rc);
244 else
245 virtqueue_kick(vioch->vqueue);
246
247 spin_unlock_irqrestore(&vioch->lock, flags);
248
249 return rc;
250 }
251
252 /*
253 * Assume to be called with channel already acquired or not ready at all;
254 * vioch->lock MUST NOT have been already acquired.
255 */
scmi_finalize_message(struct scmi_vio_channel * vioch,struct scmi_vio_msg * msg)256 static void scmi_finalize_message(struct scmi_vio_channel *vioch,
257 struct scmi_vio_msg *msg)
258 {
259 if (vioch->is_rx)
260 scmi_vio_feed_vq_rx(vioch, msg);
261 else
262 scmi_vio_msg_release(vioch, msg);
263 }
264
scmi_vio_complete_cb(struct virtqueue * vqueue)265 static void scmi_vio_complete_cb(struct virtqueue *vqueue)
266 {
267 unsigned long flags;
268 unsigned int length;
269 struct scmi_vio_channel *vioch;
270 struct scmi_vio_msg *msg;
271 bool cb_enabled = true;
272
273 if (WARN_ON_ONCE(!vqueue->vdev->priv))
274 return;
275 vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
276
277 for (;;) {
278 if (!scmi_vio_channel_acquire(vioch))
279 return;
280
281 spin_lock_irqsave(&vioch->lock, flags);
282 if (cb_enabled) {
283 virtqueue_disable_cb(vqueue);
284 cb_enabled = false;
285 }
286
287 msg = virtqueue_get_buf(vqueue, &length);
288 if (!msg) {
289 if (virtqueue_enable_cb(vqueue)) {
290 spin_unlock_irqrestore(&vioch->lock, flags);
291 scmi_vio_channel_release(vioch);
292 return;
293 }
294 cb_enabled = true;
295 }
296 spin_unlock_irqrestore(&vioch->lock, flags);
297
298 if (msg) {
299 msg->rx_len = length;
300 core->rx_callback(vioch->cinfo,
301 core->msg->read_header(msg->input),
302 msg);
303
304 scmi_finalize_message(vioch, msg);
305 }
306
307 /*
308 * Release vio channel between loop iterations to allow
309 * virtio_chan_free() to eventually fully release it when
310 * shutting down; in such a case, any outstanding message will
311 * be ignored since this loop will bail out at the next
312 * iteration.
313 */
314 scmi_vio_channel_release(vioch);
315 }
316 }
317
scmi_vio_deferred_tx_worker(struct work_struct * work)318 static void scmi_vio_deferred_tx_worker(struct work_struct *work)
319 {
320 unsigned long flags;
321 struct scmi_vio_channel *vioch;
322 struct scmi_vio_msg *msg, *tmp;
323
324 vioch = container_of(work, struct scmi_vio_channel, deferred_tx_work);
325
326 if (!scmi_vio_channel_acquire(vioch))
327 return;
328
329 /*
330 * Process pre-fetched messages: these could be non-polled messages or
331 * late timed-out replies to polled messages dequeued by chance while
332 * polling for some other messages: this worker is in charge to process
333 * the valid non-expired messages and anyway finally free all of them.
334 */
335 spin_lock_irqsave(&vioch->pending_lock, flags);
336
337 /* Scan the list of possibly pre-fetched messages during polling. */
338 list_for_each_entry_safe(msg, tmp, &vioch->pending_cmds_list, list) {
339 list_del(&msg->list);
340
341 /*
342 * Channel is acquired here (cannot vanish) and this message
343 * is no more processed elsewhere so no poll_lock needed.
344 */
345 if (msg->poll_status == VIO_MSG_NOT_POLLED)
346 core->rx_callback(vioch->cinfo,
347 core->msg->read_header(msg->input),
348 msg);
349
350 /* Free the processed message once done */
351 scmi_vio_msg_release(vioch, msg);
352 }
353
354 spin_unlock_irqrestore(&vioch->pending_lock, flags);
355
356 /* Process possibly still pending messages */
357 scmi_vio_complete_cb(vioch->vqueue);
358
359 scmi_vio_channel_release(vioch);
360 }
361
362 static struct virtqueue_info scmi_vio_vqs_info[] = {
363 { "tx", scmi_vio_complete_cb },
364 { "rx", scmi_vio_complete_cb },
365 };
366
virtio_get_max_msg(struct scmi_chan_info * base_cinfo)367 static unsigned int virtio_get_max_msg(struct scmi_chan_info *base_cinfo)
368 {
369 struct scmi_vio_channel *vioch = base_cinfo->transport_info;
370
371 return vioch->max_msg;
372 }
373
virtio_chan_available(struct device_node * of_node,int idx)374 static bool virtio_chan_available(struct device_node *of_node, int idx)
375 {
376 struct scmi_vio_channel *channels, *vioch = NULL;
377
378 if (WARN_ON_ONCE(!scmi_vdev))
379 return false;
380
381 channels = (struct scmi_vio_channel *)scmi_vdev->priv;
382
383 switch (idx) {
384 case VIRTIO_SCMI_VQ_TX:
385 vioch = &channels[VIRTIO_SCMI_VQ_TX];
386 break;
387 case VIRTIO_SCMI_VQ_RX:
388 if (scmi_vio_have_vq_rx(scmi_vdev))
389 vioch = &channels[VIRTIO_SCMI_VQ_RX];
390 break;
391 default:
392 return false;
393 }
394
395 return vioch && !vioch->cinfo;
396 }
397
scmi_destroy_tx_workqueue(void * deferred_tx_wq)398 static void scmi_destroy_tx_workqueue(void *deferred_tx_wq)
399 {
400 destroy_workqueue(deferred_tx_wq);
401 }
402
virtio_chan_setup(struct scmi_chan_info * cinfo,struct device * dev,bool tx)403 static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
404 bool tx)
405 {
406 struct scmi_vio_channel *vioch;
407 int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
408 int i;
409
410 if (!scmi_vdev)
411 return -EPROBE_DEFER;
412
413 vioch = &((struct scmi_vio_channel *)scmi_vdev->priv)[index];
414
415 /* Setup a deferred worker for polling. */
416 if (tx && !vioch->deferred_tx_wq) {
417 int ret;
418
419 vioch->deferred_tx_wq =
420 alloc_workqueue(dev_name(&scmi_vdev->dev),
421 WQ_UNBOUND | WQ_FREEZABLE | WQ_SYSFS,
422 0);
423 if (!vioch->deferred_tx_wq)
424 return -ENOMEM;
425
426 ret = devm_add_action_or_reset(dev, scmi_destroy_tx_workqueue,
427 vioch->deferred_tx_wq);
428 if (ret)
429 return ret;
430
431 INIT_WORK(&vioch->deferred_tx_work,
432 scmi_vio_deferred_tx_worker);
433 }
434
435 for (i = 0; i < vioch->max_msg; i++) {
436 struct scmi_vio_msg *msg;
437
438 msg = devm_kzalloc(dev, sizeof(*msg), GFP_KERNEL);
439 if (!msg)
440 return -ENOMEM;
441
442 if (tx) {
443 msg->request = devm_kzalloc(dev,
444 VIRTIO_SCMI_MAX_PDU_SIZE,
445 GFP_KERNEL);
446 if (!msg->request)
447 return -ENOMEM;
448 spin_lock_init(&msg->poll_lock);
449 refcount_set(&msg->users, 1);
450 }
451
452 msg->input = devm_kzalloc(dev, VIRTIO_SCMI_MAX_PDU_SIZE,
453 GFP_KERNEL);
454 if (!msg->input)
455 return -ENOMEM;
456
457 scmi_finalize_message(vioch, msg);
458 }
459
460 scmi_vio_channel_ready(vioch, cinfo);
461
462 return 0;
463 }
464
virtio_chan_free(int id,void * p,void * data)465 static int virtio_chan_free(int id, void *p, void *data)
466 {
467 struct scmi_chan_info *cinfo = p;
468 struct scmi_vio_channel *vioch = cinfo->transport_info;
469
470 /*
471 * Break device to inhibit further traffic flowing while shutting down
472 * the channels: doing it later holding vioch->lock creates unsafe
473 * locking dependency chains as reported by LOCKDEP.
474 */
475 virtio_break_device(vioch->vqueue->vdev);
476 scmi_vio_channel_cleanup_sync(vioch);
477
478 return 0;
479 }
480
virtio_send_message(struct scmi_chan_info * cinfo,struct scmi_xfer * xfer)481 static int virtio_send_message(struct scmi_chan_info *cinfo,
482 struct scmi_xfer *xfer)
483 {
484 struct scmi_vio_channel *vioch = cinfo->transport_info;
485 struct scatterlist sg_out;
486 struct scatterlist sg_in;
487 struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
488 unsigned long flags;
489 int rc;
490 struct scmi_vio_msg *msg;
491
492 if (!scmi_vio_channel_acquire(vioch))
493 return -EINVAL;
494
495 msg = scmi_virtio_get_free_msg(vioch);
496 if (!msg) {
497 scmi_vio_channel_release(vioch);
498 return -EBUSY;
499 }
500
501 core->msg->tx_prepare(msg->request, xfer);
502
503 sg_init_one(&sg_out, msg->request, core->msg->command_size(xfer));
504 sg_init_one(&sg_in, msg->input, core->msg->response_size(xfer));
505
506 spin_lock_irqsave(&vioch->lock, flags);
507
508 /*
509 * If polling was requested for this transaction:
510 * - retrieve last used index (will be used as polling reference)
511 * - bind the polled message to the xfer via .priv
512 * - grab an additional msg refcount for the poll-path
513 */
514 if (xfer->hdr.poll_completion) {
515 msg->poll_idx = virtqueue_enable_cb_prepare(vioch->vqueue);
516 /* Still no users, no need to acquire poll_lock */
517 msg->poll_status = VIO_MSG_POLLING;
518 scmi_vio_msg_acquire(msg);
519 /* Ensure initialized msg is visibly bound to xfer */
520 smp_store_mb(xfer->priv, msg);
521 }
522
523 rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
524 if (rc)
525 dev_err(vioch->cinfo->dev,
526 "failed to add to TX virtqueue (%d)\n", rc);
527 else
528 virtqueue_kick(vioch->vqueue);
529
530 spin_unlock_irqrestore(&vioch->lock, flags);
531
532 if (rc) {
533 /* Ensure order between xfer->priv clear and vq feeding */
534 smp_store_mb(xfer->priv, NULL);
535 if (xfer->hdr.poll_completion)
536 scmi_vio_msg_release(vioch, msg);
537 scmi_vio_msg_release(vioch, msg);
538 }
539
540 scmi_vio_channel_release(vioch);
541
542 return rc;
543 }
544
virtio_fetch_response(struct scmi_chan_info * cinfo,struct scmi_xfer * xfer)545 static void virtio_fetch_response(struct scmi_chan_info *cinfo,
546 struct scmi_xfer *xfer)
547 {
548 struct scmi_vio_msg *msg = xfer->priv;
549
550 if (msg)
551 core->msg->fetch_response(msg->input, msg->rx_len, xfer);
552 }
553
virtio_fetch_notification(struct scmi_chan_info * cinfo,size_t max_len,struct scmi_xfer * xfer)554 static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
555 size_t max_len, struct scmi_xfer *xfer)
556 {
557 struct scmi_vio_msg *msg = xfer->priv;
558
559 if (msg)
560 core->msg->fetch_notification(msg->input, msg->rx_len,
561 max_len, xfer);
562 }
563
564 /**
565 * virtio_mark_txdone - Mark transmission done
566 *
567 * Free only completed polling transfer messages.
568 *
569 * Note that in the SCMI VirtIO transport we never explicitly release still
570 * outstanding but timed-out messages by forcibly re-adding them to the
571 * free-list inside the TX code path; we instead let IRQ/RX callbacks, or the
572 * TX deferred worker, eventually clean up such messages once, finally, a late
573 * reply is received and discarded (if ever).
574 *
575 * This approach was deemed preferable since those pending timed-out buffers are
576 * still effectively owned by the SCMI platform VirtIO device even after timeout
577 * expiration: forcibly freeing and reusing them before they had been returned
578 * explicitly by the SCMI platform could lead to subtle bugs due to message
579 * corruption.
580 * An SCMI platform VirtIO device which never returns message buffers is
581 * anyway broken and it will quickly lead to exhaustion of available messages.
582 *
583 * For this same reason, here, we take care to free only the polled messages
584 * that had been somehow replied (only if not by chance already processed on the
585 * IRQ path - the initial scmi_vio_msg_release() takes care of this) and also
586 * any timed-out polled message if that indeed appears to have been at least
587 * dequeued from the virtqueues (VIO_MSG_POLL_DONE): this is needed since such
588 * messages won't be freed elsewhere. Any other polled message is marked as
589 * VIO_MSG_POLL_TIMEOUT.
590 *
591 * Possible late replies to timed-out polled messages will be eventually freed
592 * by RX callbacks if delivered on the IRQ path or by the deferred TX worker if
593 * dequeued on some other polling path.
594 *
595 * @cinfo: SCMI channel info
596 * @ret: Transmission return code
597 * @xfer: Transfer descriptor
598 */
virtio_mark_txdone(struct scmi_chan_info * cinfo,int ret,struct scmi_xfer * xfer)599 static void virtio_mark_txdone(struct scmi_chan_info *cinfo, int ret,
600 struct scmi_xfer *xfer)
601 {
602 unsigned long flags;
603 struct scmi_vio_channel *vioch = cinfo->transport_info;
604 struct scmi_vio_msg *msg = xfer->priv;
605
606 if (!msg || !scmi_vio_channel_acquire(vioch))
607 return;
608
609 /* Ensure msg is unbound from xfer anyway at this point */
610 smp_store_mb(xfer->priv, NULL);
611
612 /* Must be a polled xfer and not already freed on the IRQ path */
613 if (!xfer->hdr.poll_completion || scmi_vio_msg_release(vioch, msg)) {
614 scmi_vio_channel_release(vioch);
615 return;
616 }
617
618 spin_lock_irqsave(&msg->poll_lock, flags);
619 /* Do not free timedout polled messages only if still inflight */
620 if (ret != -ETIMEDOUT || msg->poll_status == VIO_MSG_POLL_DONE)
621 scmi_vio_msg_release(vioch, msg);
622 else if (msg->poll_status == VIO_MSG_POLLING)
623 msg->poll_status = VIO_MSG_POLL_TIMEOUT;
624 spin_unlock_irqrestore(&msg->poll_lock, flags);
625
626 scmi_vio_channel_release(vioch);
627 }
628
629 /**
630 * virtio_poll_done - Provide polling support for VirtIO transport
631 *
632 * @cinfo: SCMI channel info
633 * @xfer: Reference to the transfer being poll for.
634 *
635 * VirtIO core provides a polling mechanism based only on last used indexes:
636 * this means that it is possible to poll the virtqueues waiting for something
637 * new to arrive from the host side, but the only way to check if the freshly
638 * arrived buffer was indeed what we were waiting for is to compare the newly
639 * arrived message descriptor with the one we are polling on.
640 *
641 * As a consequence it can happen to dequeue something different from the buffer
642 * we were poll-waiting for: if that is the case such early fetched buffers are
643 * then added to a the @pending_cmds_list list for later processing by a
644 * dedicated deferred worker.
645 *
646 * So, basically, once something new is spotted we proceed to de-queue all the
647 * freshly received used buffers until we found the one we were polling on, or,
648 * we have 'seemingly' emptied the virtqueue; if some buffers are still pending
649 * in the vqueue at the end of the polling loop (possible due to inherent races
650 * in virtqueues handling mechanisms), we similarly kick the deferred worker
651 * and let it process those, to avoid indefinitely looping in the .poll_done
652 * busy-waiting helper.
653 *
654 * Finally, we delegate to the deferred worker also the final free of any timed
655 * out reply to a polled message that we should dequeue.
656 *
657 * Note that, since we do NOT have per-message suppress notification mechanism,
658 * the message we are polling for could be alternatively delivered via usual
659 * IRQs callbacks on another core which happened to have IRQs enabled while we
660 * are actively polling for it here: in such a case it will be handled as such
661 * by rx_callback() and the polling loop in the SCMI Core TX path will be
662 * transparently terminated anyway.
663 *
664 * Return: True once polling has successfully completed.
665 */
virtio_poll_done(struct scmi_chan_info * cinfo,struct scmi_xfer * xfer)666 static bool virtio_poll_done(struct scmi_chan_info *cinfo,
667 struct scmi_xfer *xfer)
668 {
669 bool pending, found = false;
670 unsigned int length, any_prefetched = 0;
671 unsigned long flags;
672 struct scmi_vio_msg *next_msg, *msg = xfer->priv;
673 struct scmi_vio_channel *vioch = cinfo->transport_info;
674
675 if (!msg)
676 return true;
677
678 /*
679 * Processed already by other polling loop on another CPU ?
680 *
681 * Note that this message is acquired on the poll path so cannot vanish
682 * while inside this loop iteration even if concurrently processed on
683 * the IRQ path.
684 *
685 * Avoid to acquire poll_lock since polled_status can be changed
686 * in a relevant manner only later in this same thread of execution:
687 * any other possible changes made concurrently by other polling loops
688 * or by a reply delivered on the IRQ path have no meaningful impact on
689 * this loop iteration: in other words it is harmless to allow this
690 * possible race but let has avoid spinlocking with irqs off in this
691 * initial part of the polling loop.
692 */
693 if (msg->poll_status == VIO_MSG_POLL_DONE)
694 return true;
695
696 if (!scmi_vio_channel_acquire(vioch))
697 return true;
698
699 /* Has cmdq index moved at all ? */
700 pending = virtqueue_poll(vioch->vqueue, msg->poll_idx);
701 if (!pending) {
702 scmi_vio_channel_release(vioch);
703 return false;
704 }
705
706 spin_lock_irqsave(&vioch->lock, flags);
707 virtqueue_disable_cb(vioch->vqueue);
708
709 /*
710 * Process all new messages till the polled-for message is found OR
711 * the vqueue is empty.
712 */
713 while ((next_msg = virtqueue_get_buf(vioch->vqueue, &length))) {
714 bool next_msg_done = false;
715
716 /*
717 * Mark any dequeued buffer message as VIO_MSG_POLL_DONE so
718 * that can be properly freed even on timeout in mark_txdone.
719 */
720 spin_lock(&next_msg->poll_lock);
721 if (next_msg->poll_status == VIO_MSG_POLLING) {
722 next_msg->poll_status = VIO_MSG_POLL_DONE;
723 next_msg_done = true;
724 }
725 spin_unlock(&next_msg->poll_lock);
726
727 next_msg->rx_len = length;
728 /* Is the message we were polling for ? */
729 if (next_msg == msg) {
730 found = true;
731 break;
732 } else if (next_msg_done) {
733 /* Skip the rest if this was another polled msg */
734 continue;
735 }
736
737 /*
738 * Enqueue for later processing any non-polled message and any
739 * timed-out polled one that we happen to have dequeued.
740 */
741 spin_lock(&next_msg->poll_lock);
742 if (next_msg->poll_status == VIO_MSG_NOT_POLLED ||
743 next_msg->poll_status == VIO_MSG_POLL_TIMEOUT) {
744 spin_unlock(&next_msg->poll_lock);
745
746 any_prefetched++;
747 spin_lock(&vioch->pending_lock);
748 list_add_tail(&next_msg->list,
749 &vioch->pending_cmds_list);
750 spin_unlock(&vioch->pending_lock);
751 } else {
752 spin_unlock(&next_msg->poll_lock);
753 }
754 }
755
756 /*
757 * When the polling loop has successfully terminated if something
758 * else was queued in the meantime, it will be served by a deferred
759 * worker OR by the normal IRQ/callback OR by other poll loops.
760 *
761 * If we are still looking for the polled reply, the polling index has
762 * to be updated to the current vqueue last used index.
763 */
764 if (found) {
765 pending = !virtqueue_enable_cb(vioch->vqueue);
766 } else {
767 msg->poll_idx = virtqueue_enable_cb_prepare(vioch->vqueue);
768 pending = virtqueue_poll(vioch->vqueue, msg->poll_idx);
769 }
770
771 if (vioch->deferred_tx_wq && (any_prefetched || pending))
772 queue_work(vioch->deferred_tx_wq, &vioch->deferred_tx_work);
773
774 spin_unlock_irqrestore(&vioch->lock, flags);
775
776 scmi_vio_channel_release(vioch);
777
778 return found;
779 }
780
781 static const struct scmi_transport_ops scmi_virtio_ops = {
782 .chan_available = virtio_chan_available,
783 .chan_setup = virtio_chan_setup,
784 .chan_free = virtio_chan_free,
785 .get_max_msg = virtio_get_max_msg,
786 .send_message = virtio_send_message,
787 .fetch_response = virtio_fetch_response,
788 .fetch_notification = virtio_fetch_notification,
789 .mark_txdone = virtio_mark_txdone,
790 .poll_done = virtio_poll_done,
791 };
792
793 static struct scmi_desc scmi_virtio_desc = {
794 .ops = &scmi_virtio_ops,
795 /* for non-realtime virtio devices */
796 .max_rx_timeout_ms = VIRTIO_MAX_RX_TIMEOUT_MS,
797 .max_msg = 0, /* overridden by virtio_get_max_msg() */
798 .max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
799 .atomic_enabled = IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE),
800 };
801
802 static const struct of_device_id scmi_of_match[] = {
803 { .compatible = "arm,scmi-virtio" },
804 { /* Sentinel */ },
805 };
806
807 DEFINE_SCMI_TRANSPORT_DRIVER(scmi_virtio, scmi_virtio_driver, scmi_virtio_desc,
808 scmi_of_match, core);
809
scmi_vio_probe(struct virtio_device * vdev)810 static int scmi_vio_probe(struct virtio_device *vdev)
811 {
812 struct device *dev = &vdev->dev;
813 struct scmi_vio_channel *channels;
814 bool have_vq_rx;
815 int vq_cnt;
816 int i;
817 int ret;
818 struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
819
820 /* Only one SCMI VirtiO device allowed */
821 if (scmi_vdev) {
822 dev_err(dev,
823 "One SCMI Virtio device was already initialized: only one allowed.\n");
824 return -EBUSY;
825 }
826
827 have_vq_rx = scmi_vio_have_vq_rx(vdev);
828 vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
829
830 channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
831 if (!channels)
832 return -ENOMEM;
833
834 if (have_vq_rx)
835 channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
836
837 ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_vqs_info, NULL);
838 if (ret) {
839 dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
840 return ret;
841 }
842
843 for (i = 0; i < vq_cnt; i++) {
844 unsigned int sz;
845
846 spin_lock_init(&channels[i].lock);
847 spin_lock_init(&channels[i].free_lock);
848 INIT_LIST_HEAD(&channels[i].free_list);
849 spin_lock_init(&channels[i].pending_lock);
850 INIT_LIST_HEAD(&channels[i].pending_cmds_list);
851 channels[i].vqueue = vqs[i];
852
853 sz = virtqueue_get_vring_size(channels[i].vqueue);
854 /* Tx messages need multiple descriptors. */
855 if (!channels[i].is_rx)
856 sz /= DESCRIPTORS_PER_TX_MSG;
857
858 if (sz > MSG_TOKEN_MAX) {
859 dev_info(dev,
860 "%s virtqueue could hold %d messages. Only %ld allowed to be pending.\n",
861 channels[i].is_rx ? "rx" : "tx",
862 sz, MSG_TOKEN_MAX);
863 sz = MSG_TOKEN_MAX;
864 }
865 channels[i].max_msg = sz;
866 }
867
868 vdev->priv = channels;
869
870 /* Ensure initialized scmi_vdev is visible */
871 smp_store_mb(scmi_vdev, vdev);
872
873 ret = platform_driver_register(&scmi_virtio_driver);
874 if (ret) {
875 vdev->priv = NULL;
876 vdev->config->del_vqs(vdev);
877 /* Ensure NULLified scmi_vdev is visible */
878 smp_store_mb(scmi_vdev, NULL);
879
880 return ret;
881 }
882
883 return 0;
884 }
885
scmi_vio_remove(struct virtio_device * vdev)886 static void scmi_vio_remove(struct virtio_device *vdev)
887 {
888 platform_driver_unregister(&scmi_virtio_driver);
889
890 /*
891 * Once we get here, virtio_chan_free() will have already been called by
892 * the SCMI core for any existing channel and, as a consequence, all the
893 * virtio channels will have been already marked NOT ready, causing any
894 * outstanding message on any vqueue to be ignored by complete_cb: now
895 * we can just stop processing buffers and destroy the vqueues.
896 */
897 virtio_reset_device(vdev);
898 vdev->config->del_vqs(vdev);
899 /* Ensure scmi_vdev is visible as NULL */
900 smp_store_mb(scmi_vdev, NULL);
901 }
902
scmi_vio_validate(struct virtio_device * vdev)903 static int scmi_vio_validate(struct virtio_device *vdev)
904 {
905 #ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_VERSION1_COMPLIANCE
906 if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
907 dev_err(&vdev->dev,
908 "device does not comply with spec version 1.x\n");
909 return -EINVAL;
910 }
911 #endif
912 return 0;
913 }
914
915 static unsigned int features[] = {
916 VIRTIO_SCMI_F_P2A_CHANNELS,
917 };
918
919 static const struct virtio_device_id id_table[] = {
920 { VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
921 { 0 }
922 };
923
924 static struct virtio_driver virtio_scmi_driver = {
925 .driver.name = "scmi-virtio",
926 .feature_table = features,
927 .feature_table_size = ARRAY_SIZE(features),
928 .id_table = id_table,
929 .probe = scmi_vio_probe,
930 .remove = scmi_vio_remove,
931 .validate = scmi_vio_validate,
932 };
933
934 module_virtio_driver(virtio_scmi_driver);
935
936 MODULE_AUTHOR("Igor Skalkin <igor.skalkin@opensynergy.com>");
937 MODULE_AUTHOR("Peter Hilber <peter.hilber@opensynergy.com>");
938 MODULE_AUTHOR("Cristian Marussi <cristian.marussi@arm.com>");
939 MODULE_DESCRIPTION("SCMI VirtIO Transport driver");
940 MODULE_LICENSE("GPL");
941