virtio.c

  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(ci) \
 36	((ci)->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 */
 57struct 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
 79enum 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 * @max_len: Maximumm allowed SDU size in bytes
 94 * @poll_idx: Last used index registered for polling purposes if this message
 95 *	      transaction reply was configured for polling.
 96 * @poll_status: Polling state for this message.
 97 * @poll_lock: A lock to protect @poll_status
 98 * @users: A reference count to track this message users and avoid premature
 99 *	   freeing (and reuse) when polling and IRQ execution paths interleave.
100 */
101struct scmi_vio_msg {
102	struct scmi_msg_payld *request;
103	struct scmi_msg_payld *input;
104	struct list_head list;
105	unsigned int rx_len;
106	unsigned int max_len;
107	unsigned int poll_idx;
108	enum poll_states poll_status;
109	/* Lock to protect access to poll_status */
110	spinlock_t poll_lock;
111	refcount_t users;
112};
113
114static struct scmi_transport_core_operations *core;
115
116/* Only one SCMI VirtIO device can possibly exist */
117static struct virtio_device *scmi_vdev;
118
119static void scmi_vio_channel_ready(struct scmi_vio_channel *vioch,
120				   struct scmi_chan_info *cinfo)
121{
122	unsigned long flags;
123
124	spin_lock_irqsave(&vioch->lock, flags);
125	cinfo->transport_info = vioch;
126	/* Indirectly setting channel not available any more */
127	vioch->cinfo = cinfo;
128	spin_unlock_irqrestore(&vioch->lock, flags);
129
130	refcount_set(&vioch->users, 1);
131}
132
133static inline bool scmi_vio_channel_acquire(struct scmi_vio_channel *vioch)
134{
135	return refcount_inc_not_zero(&vioch->users);
136}
137
138static inline void scmi_vio_channel_release(struct scmi_vio_channel *vioch)
139{
140	if (refcount_dec_and_test(&vioch->users)) {
141		unsigned long flags;
142
143		spin_lock_irqsave(&vioch->lock, flags);
144		if (vioch->shutdown_done) {
145			vioch->cinfo = NULL;
146			complete(vioch->shutdown_done);
147		}
148		spin_unlock_irqrestore(&vioch->lock, flags);
149	}
150}
151
152static void scmi_vio_channel_cleanup_sync(struct scmi_vio_channel *vioch)
153{
154	unsigned long flags;
155	DECLARE_COMPLETION_ONSTACK(vioch_shutdown_done);
156
157	/*
158	 * Prepare to wait for the last release if not already released
159	 * or in progress.
160	 */
161	spin_lock_irqsave(&vioch->lock, flags);
162	if (!vioch->cinfo || vioch->shutdown_done) {
163		spin_unlock_irqrestore(&vioch->lock, flags);
164		return;
165	}
166
167	vioch->shutdown_done = &vioch_shutdown_done;
168	if (!vioch->is_rx && vioch->deferred_tx_wq)
169		/* Cannot be kicked anymore after this...*/
170		vioch->deferred_tx_wq = NULL;
171	spin_unlock_irqrestore(&vioch->lock, flags);
172
173	scmi_vio_channel_release(vioch);
174
175	/* Let any possibly concurrent RX path release the channel */
176	wait_for_completion(vioch->shutdown_done);
177}
178
179/* Assumes to be called with vio channel acquired already */
180static struct scmi_vio_msg *
181scmi_virtio_get_free_msg(struct scmi_vio_channel *vioch)
182{
183	unsigned long flags;
184	struct scmi_vio_msg *msg;
185
186	spin_lock_irqsave(&vioch->free_lock, flags);
187	if (list_empty(&vioch->free_list)) {
188		spin_unlock_irqrestore(&vioch->free_lock, flags);
189		return NULL;
190	}
191
192	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
193	list_del_init(&msg->list);
194	spin_unlock_irqrestore(&vioch->free_lock, flags);
195
196	/* Still no users, no need to acquire poll_lock */
197	msg->poll_status = VIO_MSG_NOT_POLLED;
198	refcount_set(&msg->users, 1);
199
200	return msg;
201}
202
203static inline bool scmi_vio_msg_acquire(struct scmi_vio_msg *msg)
204{
205	return refcount_inc_not_zero(&msg->users);
206}
207
208/* Assumes to be called with vio channel acquired already */
209static inline bool scmi_vio_msg_release(struct scmi_vio_channel *vioch,
210					struct scmi_vio_msg *msg)
211{
212	bool ret;
213
214	ret = refcount_dec_and_test(&msg->users);
215	if (ret) {
216		unsigned long flags;
217
218		spin_lock_irqsave(&vioch->free_lock, flags);
219		list_add_tail(&msg->list, &vioch->free_list);
220		spin_unlock_irqrestore(&vioch->free_lock, flags);
221	}
222
223	return ret;
224}
225
226static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
227{
228	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
229}
230
231static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
232			       struct scmi_vio_msg *msg)
233{
234	struct scatterlist sg_in;
235	int rc;
236	unsigned long flags;
237	struct device *dev = &vioch->vqueue->vdev->dev;
238
239	sg_init_one(&sg_in, msg->input, msg->max_len);
240
241	spin_lock_irqsave(&vioch->lock, flags);
242
243	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
244	if (rc)
245		dev_err(dev, "failed to add to RX virtqueue (%d)\n", rc);
246	else
247		virtqueue_kick(vioch->vqueue);
248
249	spin_unlock_irqrestore(&vioch->lock, flags);
250
251	return rc;
252}
253
254/*
255 * Assume to be called with channel already acquired or not ready at all;
256 * vioch->lock MUST NOT have been already acquired.
257 */
258static void scmi_finalize_message(struct scmi_vio_channel *vioch,
259				  struct scmi_vio_msg *msg)
260{
261	if (vioch->is_rx)
262		scmi_vio_feed_vq_rx(vioch, msg);
263	else
264		scmi_vio_msg_release(vioch, msg);
265}
266
267static void scmi_vio_complete_cb(struct virtqueue *vqueue)
268{
269	unsigned long flags;
270	unsigned int length;
271	struct scmi_vio_channel *vioch;
272	struct scmi_vio_msg *msg;
273	bool cb_enabled = true;
274
275	if (WARN_ON_ONCE(!vqueue->vdev->priv))
276		return;
277	vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
278
279	for (;;) {
280		if (!scmi_vio_channel_acquire(vioch))
281			return;
282
283		spin_lock_irqsave(&vioch->lock, flags);
284		if (cb_enabled) {
285			virtqueue_disable_cb(vqueue);
286			cb_enabled = false;
287		}
288
289		msg = virtqueue_get_buf(vqueue, &length);
290		if (!msg) {
291			if (virtqueue_enable_cb(vqueue)) {
292				spin_unlock_irqrestore(&vioch->lock, flags);
293				scmi_vio_channel_release(vioch);
294				return;
295			}
296			cb_enabled = true;
297		}
298		spin_unlock_irqrestore(&vioch->lock, flags);
299
300		if (msg) {
301			msg->rx_len = length;
302			core->rx_callback(vioch->cinfo,
303					  core->msg->read_header(msg->input),
304					  msg);
305
306			scmi_finalize_message(vioch, msg);
307		}
308
309		/*
310		 * Release vio channel between loop iterations to allow
311		 * virtio_chan_free() to eventually fully release it when
312		 * shutting down; in such a case, any outstanding message will
313		 * be ignored since this loop will bail out at the next
314		 * iteration.
315		 */
316		scmi_vio_channel_release(vioch);
317	}
318}
319
320static void scmi_vio_deferred_tx_worker(struct work_struct *work)
321{
322	unsigned long flags;
323	struct scmi_vio_channel *vioch;
324	struct scmi_vio_msg *msg, *tmp;
325
326	vioch = container_of(work, struct scmi_vio_channel, deferred_tx_work);
327
328	if (!scmi_vio_channel_acquire(vioch))
329		return;
330
331	/*
332	 * Process pre-fetched messages: these could be non-polled messages or
333	 * late timed-out replies to polled messages dequeued by chance while
334	 * polling for some other messages: this worker is in charge to process
335	 * the valid non-expired messages and anyway finally free all of them.
336	 */
337	spin_lock_irqsave(&vioch->pending_lock, flags);
338
339	/* Scan the list of possibly pre-fetched messages during polling. */
340	list_for_each_entry_safe(msg, tmp, &vioch->pending_cmds_list, list) {
341		list_del(&msg->list);
342
343		/*
344		 * Channel is acquired here (cannot vanish) and this message
345		 * is no more processed elsewhere so no poll_lock needed.
346		 */
347		if (msg->poll_status == VIO_MSG_NOT_POLLED)
348			core->rx_callback(vioch->cinfo,
349					  core->msg->read_header(msg->input),
350					  msg);
351
352		/* Free the processed message once done */
353		scmi_vio_msg_release(vioch, msg);
354	}
355
356	spin_unlock_irqrestore(&vioch->pending_lock, flags);
357
358	/* Process possibly still pending messages */
359	scmi_vio_complete_cb(vioch->vqueue);
360
361	scmi_vio_channel_release(vioch);
362}
363
364static struct virtqueue_info scmi_vio_vqs_info[] = {
365	{ "tx", scmi_vio_complete_cb },
366	{ "rx", scmi_vio_complete_cb },
367};
368
369static unsigned int virtio_get_max_msg(struct scmi_chan_info *base_cinfo)
370{
371	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
372
373	return vioch->max_msg;
374}
375
376static bool virtio_chan_available(struct device_node *of_node, int idx)
377{
378	struct scmi_vio_channel *channels, *vioch = NULL;
379
380	if (WARN_ON_ONCE(!scmi_vdev))
381		return false;
382
383	channels = (struct scmi_vio_channel *)scmi_vdev->priv;
384
385	switch (idx) {
386	case VIRTIO_SCMI_VQ_TX:
387		vioch = &channels[VIRTIO_SCMI_VQ_TX];
388		break;
389	case VIRTIO_SCMI_VQ_RX:
390		if (scmi_vio_have_vq_rx(scmi_vdev))
391			vioch = &channels[VIRTIO_SCMI_VQ_RX];
392		break;
393	default:
394		return false;
395	}
396
397	return vioch && !vioch->cinfo;
398}
399
400static void scmi_destroy_tx_workqueue(void *deferred_tx_wq)
401{
402	destroy_workqueue(deferred_tx_wq);
403}
404
405static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
406			     bool tx)
407{
408	struct scmi_vio_channel *vioch;
409	int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
410	int i;
411
412	if (!scmi_vdev)
413		return -EPROBE_DEFER;
414
415	vioch = &((struct scmi_vio_channel *)scmi_vdev->priv)[index];
416
417	/* Setup a deferred worker for polling. */
418	if (tx && !vioch->deferred_tx_wq) {
419		int ret;
420
421		vioch->deferred_tx_wq =
422			alloc_workqueue(dev_name(&scmi_vdev->dev),
423					WQ_UNBOUND | WQ_FREEZABLE | WQ_SYSFS,
424					0);
425		if (!vioch->deferred_tx_wq)
426			return -ENOMEM;
427
428		ret = devm_add_action_or_reset(dev, scmi_destroy_tx_workqueue,
429					       vioch->deferred_tx_wq);
430		if (ret)
431			return ret;
432
433		INIT_WORK(&vioch->deferred_tx_work,
434			  scmi_vio_deferred_tx_worker);
435	}
436
437	for (i = 0; i < vioch->max_msg; i++) {
438		struct scmi_vio_msg *msg;
439
440		msg = devm_kzalloc(dev, sizeof(*msg), GFP_KERNEL);
441		if (!msg)
442			return -ENOMEM;
443
444		msg->max_len = VIRTIO_SCMI_MAX_PDU_SIZE(cinfo);
445		if (tx) {
446			msg->request = devm_kzalloc(dev, msg->max_len,
447						    GFP_KERNEL);
448			if (!msg->request)
449				return -ENOMEM;
450			spin_lock_init(&msg->poll_lock);
451			refcount_set(&msg->users, 1);
452		}
453
454		msg->input = devm_kzalloc(dev, msg->max_len, GFP_KERNEL);
455		if (!msg->input)
456			return -ENOMEM;
457
458		scmi_finalize_message(vioch, msg);
459	}
460
461	scmi_vio_channel_ready(vioch, cinfo);
462
463	return 0;
464}
465
466static int virtio_chan_free(int id, void *p, void *data)
467{
468	struct scmi_chan_info *cinfo = p;
469	struct scmi_vio_channel *vioch = cinfo->transport_info;
470
471	/*
472	 * Break device to inhibit further traffic flowing while shutting down
473	 * the channels: doing it later holding vioch->lock creates unsafe
474	 * locking dependency chains as reported by LOCKDEP.
475	 */
476	virtio_break_device(vioch->vqueue->vdev);
477	scmi_vio_channel_cleanup_sync(vioch);
478
479	return 0;
480}
481
482static int virtio_send_message(struct scmi_chan_info *cinfo,
483			       struct scmi_xfer *xfer)
484{
485	struct scmi_vio_channel *vioch = cinfo->transport_info;
486	struct scatterlist sg_out;
487	struct scatterlist sg_in;
488	struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
489	unsigned long flags;
490	int rc;
491	struct scmi_vio_msg *msg;
492
493	if (!scmi_vio_channel_acquire(vioch))
494		return -EINVAL;
495
496	msg = scmi_virtio_get_free_msg(vioch);
497	if (!msg) {
498		scmi_vio_channel_release(vioch);
499		return -EBUSY;
500	}
501
502	core->msg->tx_prepare(msg->request, xfer);
503
504	sg_init_one(&sg_out, msg->request, core->msg->command_size(xfer));
505	sg_init_one(&sg_in, msg->input, core->msg->response_size(xfer));
506
507	spin_lock_irqsave(&vioch->lock, flags);
508
509	/*
510	 * If polling was requested for this transaction:
511	 *  - retrieve last used index (will be used as polling reference)
512	 *  - bind the polled message to the xfer via .priv
513	 *  - grab an additional msg refcount for the poll-path
514	 */
515	if (xfer->hdr.poll_completion) {
516		msg->poll_idx = virtqueue_enable_cb_prepare(vioch->vqueue);
517		/* Still no users, no need to acquire poll_lock */
518		msg->poll_status = VIO_MSG_POLLING;
519		scmi_vio_msg_acquire(msg);
520		/* Ensure initialized msg is visibly bound to xfer */
521		smp_store_mb(xfer->priv, msg);
522	}
523
524	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
525	if (rc)
526		dev_err(vioch->cinfo->dev,
527			"failed to add to TX virtqueue (%d)\n", rc);
528	else
529		virtqueue_kick(vioch->vqueue);
530
531	spin_unlock_irqrestore(&vioch->lock, flags);
532
533	if (rc) {
534		/* Ensure order between xfer->priv clear and vq feeding */
535		smp_store_mb(xfer->priv, NULL);
536		if (xfer->hdr.poll_completion)
537			scmi_vio_msg_release(vioch, msg);
538		scmi_vio_msg_release(vioch, msg);
539	}
540
541	scmi_vio_channel_release(vioch);
542
543	return rc;
544}
545
546static void virtio_fetch_response(struct scmi_chan_info *cinfo,
547				  struct scmi_xfer *xfer)
548{
549	struct scmi_vio_msg *msg = xfer->priv;
550
551	if (msg)
552		core->msg->fetch_response(msg->input, msg->rx_len, xfer);
553}
554
555static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
556				      size_t max_len, struct scmi_xfer *xfer)
557{
558	struct scmi_vio_msg *msg = xfer->priv;
559
560	if (msg)
561		core->msg->fetch_notification(msg->input, msg->rx_len,
562					      max_len, xfer);
563}
564
565/**
566 * virtio_mark_txdone  - Mark transmission done
567 *
568 * Free only completed polling transfer messages.
569 *
570 * Note that in the SCMI VirtIO transport we never explicitly release still
571 * outstanding but timed-out messages by forcibly re-adding them to the
572 * free-list inside the TX code path; we instead let IRQ/RX callbacks, or the
573 * TX deferred worker, eventually clean up such messages once, finally, a late
574 * reply is received and discarded (if ever).
575 *
576 * This approach was deemed preferable since those pending timed-out buffers are
577 * still effectively owned by the SCMI platform VirtIO device even after timeout
578 * expiration: forcibly freeing and reusing them before they had been returned
579 * explicitly by the SCMI platform could lead to subtle bugs due to message
580 * corruption.
581 * An SCMI platform VirtIO device which never returns message buffers is
582 * anyway broken and it will quickly lead to exhaustion of available messages.
583 *
584 * For this same reason, here, we take care to free only the polled messages
585 * that had been somehow replied (only if not by chance already processed on the
586 * IRQ path - the initial scmi_vio_msg_release() takes care of this) and also
587 * any timed-out polled message if that indeed appears to have been at least
588 * dequeued from the virtqueues (VIO_MSG_POLL_DONE): this is needed since such
589 * messages won't be freed elsewhere. Any other polled message is marked as
590 * VIO_MSG_POLL_TIMEOUT.
591 *
592 * Possible late replies to timed-out polled messages will be eventually freed
593 * by RX callbacks if delivered on the IRQ path or by the deferred TX worker if
594 * dequeued on some other polling path.
595 *
596 * @cinfo: SCMI channel info
597 * @ret: Transmission return code
598 * @xfer: Transfer descriptor
599 */
600static void virtio_mark_txdone(struct scmi_chan_info *cinfo, int ret,
601			       struct scmi_xfer *xfer)
602{
603	unsigned long flags;
604	struct scmi_vio_channel *vioch = cinfo->transport_info;
605	struct scmi_vio_msg *msg = xfer->priv;
606
607	if (!msg || !scmi_vio_channel_acquire(vioch))
608		return;
609
610	/* Ensure msg is unbound from xfer anyway at this point */
611	smp_store_mb(xfer->priv, NULL);
612
613	/* Must be a polled xfer and not already freed on the IRQ path */
614	if (!xfer->hdr.poll_completion || scmi_vio_msg_release(vioch, msg)) {
615		scmi_vio_channel_release(vioch);
616		return;
617	}
618
619	spin_lock_irqsave(&msg->poll_lock, flags);
620	/* Do not free timedout polled messages only if still inflight */
621	if (ret != -ETIMEDOUT || msg->poll_status == VIO_MSG_POLL_DONE)
622		scmi_vio_msg_release(vioch, msg);
623	else if (msg->poll_status == VIO_MSG_POLLING)
624		msg->poll_status = VIO_MSG_POLL_TIMEOUT;
625	spin_unlock_irqrestore(&msg->poll_lock, flags);
626
627	scmi_vio_channel_release(vioch);
628}
629
630/**
631 * virtio_poll_done  - Provide polling support for VirtIO transport
632 *
633 * @cinfo: SCMI channel info
634 * @xfer: Reference to the transfer being poll for.
635 *
636 * VirtIO core provides a polling mechanism based only on last used indexes:
637 * this means that it is possible to poll the virtqueues waiting for something
638 * new to arrive from the host side, but the only way to check if the freshly
639 * arrived buffer was indeed what we were waiting for is to compare the newly
640 * arrived message descriptor with the one we are polling on.
641 *
642 * As a consequence it can happen to dequeue something different from the buffer
643 * we were poll-waiting for: if that is the case such early fetched buffers are
644 * then added to a the @pending_cmds_list list for later processing by a
645 * dedicated deferred worker.
646 *
647 * So, basically, once something new is spotted we proceed to de-queue all the
648 * freshly received used buffers until we found the one we were polling on, or,
649 * we have 'seemingly' emptied the virtqueue; if some buffers are still pending
650 * in the vqueue at the end of the polling loop (possible due to inherent races
651 * in virtqueues handling mechanisms), we similarly kick the deferred worker
652 * and let it process those, to avoid indefinitely looping in the .poll_done
653 * busy-waiting helper.
654 *
655 * Finally, we delegate to the deferred worker also the final free of any timed
656 * out reply to a polled message that we should dequeue.
657 *
658 * Note that, since we do NOT have per-message suppress notification mechanism,
659 * the message we are polling for could be alternatively delivered via usual
660 * IRQs callbacks on another core which happened to have IRQs enabled while we
661 * are actively polling for it here: in such a case it will be handled as such
662 * by rx_callback() and the polling loop in the SCMI Core TX path will be
663 * transparently terminated anyway.
664 *
665 * Return: True once polling has successfully completed.
666 */
667static bool virtio_poll_done(struct scmi_chan_info *cinfo,
668			     struct scmi_xfer *xfer)
669{
670	bool pending, found = false;
671	unsigned int length, any_prefetched = 0;
672	unsigned long flags;
673	struct scmi_vio_msg *next_msg, *msg = xfer->priv;
674	struct scmi_vio_channel *vioch = cinfo->transport_info;
675
676	if (!msg)
677		return true;
678
679	/*
680	 * Processed already by other polling loop on another CPU ?
681	 *
682	 * Note that this message is acquired on the poll path so cannot vanish
683	 * while inside this loop iteration even if concurrently processed on
684	 * the IRQ path.
685	 *
686	 * Avoid to acquire poll_lock since polled_status can be changed
687	 * in a relevant manner only later in this same thread of execution:
688	 * any other possible changes made concurrently by other polling loops
689	 * or by a reply delivered on the IRQ path have no meaningful impact on
690	 * this loop iteration: in other words it is harmless to allow this
691	 * possible race but let has avoid spinlocking with irqs off in this
692	 * initial part of the polling loop.
693	 */
694	if (msg->poll_status == VIO_MSG_POLL_DONE)
695		return true;
696
697	if (!scmi_vio_channel_acquire(vioch))
698		return true;
699
700	/* Has cmdq index moved at all ? */
701	pending = virtqueue_poll(vioch->vqueue, msg->poll_idx);
702	if (!pending) {
703		scmi_vio_channel_release(vioch);
704		return false;
705	}
706
707	spin_lock_irqsave(&vioch->lock, flags);
708	virtqueue_disable_cb(vioch->vqueue);
709
710	/*
711	 * Process all new messages till the polled-for message is found OR
712	 * the vqueue is empty.
713	 */
714	while ((next_msg = virtqueue_get_buf(vioch->vqueue, &length))) {
715		bool next_msg_done = false;
716
717		/*
718		 * Mark any dequeued buffer message as VIO_MSG_POLL_DONE so
719		 * that can be properly freed even on timeout in mark_txdone.
720		 */
721		spin_lock(&next_msg->poll_lock);
722		if (next_msg->poll_status == VIO_MSG_POLLING) {
723			next_msg->poll_status = VIO_MSG_POLL_DONE;
724			next_msg_done = true;
725		}
726		spin_unlock(&next_msg->poll_lock);
727
728		next_msg->rx_len = length;
729		/* Is the message we were polling for ? */
730		if (next_msg == msg) {
731			found = true;
732			break;
733		} else if (next_msg_done) {
734			/* Skip the rest if this was another polled msg */
735			continue;
736		}
737
738		/*
739		 * Enqueue for later processing any non-polled message and any
740		 * timed-out polled one that we happen to have dequeued.
741		 */
742		spin_lock(&next_msg->poll_lock);
743		if (next_msg->poll_status == VIO_MSG_NOT_POLLED ||
744		    next_msg->poll_status == VIO_MSG_POLL_TIMEOUT) {
745			spin_unlock(&next_msg->poll_lock);
746
747			any_prefetched++;
748			spin_lock(&vioch->pending_lock);
749			list_add_tail(&next_msg->list,
750				      &vioch->pending_cmds_list);
751			spin_unlock(&vioch->pending_lock);
752		} else {
753			spin_unlock(&next_msg->poll_lock);
754		}
755	}
756
757	/*
758	 * When the polling loop has successfully terminated if something
759	 * else was queued in the meantime, it will be served by a deferred
760	 * worker OR by the normal IRQ/callback OR by other poll loops.
761	 *
762	 * If we are still looking for the polled reply, the polling index has
763	 * to be updated to the current vqueue last used index.
764	 */
765	if (found) {
766		pending = !virtqueue_enable_cb(vioch->vqueue);
767	} else {
768		msg->poll_idx = virtqueue_enable_cb_prepare(vioch->vqueue);
769		pending = virtqueue_poll(vioch->vqueue, msg->poll_idx);
770	}
771
772	if (vioch->deferred_tx_wq && (any_prefetched || pending))
773		queue_work(vioch->deferred_tx_wq, &vioch->deferred_tx_work);
774
775	spin_unlock_irqrestore(&vioch->lock, flags);
776
777	scmi_vio_channel_release(vioch);
778
779	return found;
780}
781
782static const struct scmi_transport_ops scmi_virtio_ops = {
783	.chan_available = virtio_chan_available,
784	.chan_setup = virtio_chan_setup,
785	.chan_free = virtio_chan_free,
786	.get_max_msg = virtio_get_max_msg,
787	.send_message = virtio_send_message,
788	.fetch_response = virtio_fetch_response,
789	.fetch_notification = virtio_fetch_notification,
790	.mark_txdone = virtio_mark_txdone,
791	.poll_done = virtio_poll_done,
792};
793
794static struct scmi_desc scmi_virtio_desc = {
795	.ops = &scmi_virtio_ops,
796	/* for non-realtime virtio devices */
797	.max_rx_timeout_ms = VIRTIO_MAX_RX_TIMEOUT_MS,
798	.max_msg = 0, /* overridden by virtio_get_max_msg() */
799	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
800	.atomic_enabled = IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE),
801};
802
803static const struct of_device_id scmi_of_match[] = {
804	{ .compatible = "arm,scmi-virtio" },
805	{ /* Sentinel */ },
806};
807
808DEFINE_SCMI_TRANSPORT_DRIVER(scmi_virtio, scmi_virtio_driver, scmi_virtio_desc,
809			     scmi_of_match, core);
810
811static int scmi_vio_probe(struct virtio_device *vdev)
812{
813	struct device *dev = &vdev->dev;
814	struct scmi_vio_channel *channels;
815	bool have_vq_rx;
816	int vq_cnt;
817	int i;
818	int ret;
819	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
820
821	/* Only one SCMI VirtiO device allowed */
822	if (scmi_vdev) {
823		dev_err(dev,
824			"One SCMI Virtio device was already initialized: only one allowed.\n");
825		return -EBUSY;
826	}
827
828	have_vq_rx = scmi_vio_have_vq_rx(vdev);
829	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
830
831	channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
832	if (!channels)
833		return -ENOMEM;
834
835	if (have_vq_rx)
836		channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
837
838	ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_vqs_info, NULL);
839	if (ret) {
840		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
841		return ret;
842	}
843
844	for (i = 0; i < vq_cnt; i++) {
845		unsigned int sz;
846
847		spin_lock_init(&channels[i].lock);
848		spin_lock_init(&channels[i].free_lock);
849		INIT_LIST_HEAD(&channels[i].free_list);
850		spin_lock_init(&channels[i].pending_lock);
851		INIT_LIST_HEAD(&channels[i].pending_cmds_list);
852		channels[i].vqueue = vqs[i];
853
854		sz = virtqueue_get_vring_size(channels[i].vqueue);
855		/* Tx messages need multiple descriptors. */
856		if (!channels[i].is_rx)
857			sz /= DESCRIPTORS_PER_TX_MSG;
858
859		if (sz > MSG_TOKEN_MAX) {
860			dev_info(dev,
861				 "%s virtqueue could hold %d messages. Only %ld allowed to be pending.\n",
862				 channels[i].is_rx ? "rx" : "tx",
863				 sz, MSG_TOKEN_MAX);
864			sz = MSG_TOKEN_MAX;
865		}
866		channels[i].max_msg = sz;
867	}
868
869	vdev->priv = channels;
870
871	/* Ensure initialized scmi_vdev is visible */
872	smp_store_mb(scmi_vdev, vdev);
873
874	/* Set device ready */
875	virtio_device_ready(vdev);
876
877	ret = platform_driver_register(&scmi_virtio_driver);
878	if (ret) {
879		vdev->priv = NULL;
880		vdev->config->del_vqs(vdev);
881		/* Ensure NULLified scmi_vdev is visible */
882		smp_store_mb(scmi_vdev, NULL);
883
884		return ret;
885	}
886
887	return 0;
888}
889
890static void scmi_vio_remove(struct virtio_device *vdev)
891{
892	platform_driver_unregister(&scmi_virtio_driver);
893
894	/*
895	 * Once we get here, virtio_chan_free() will have already been called by
896	 * the SCMI core for any existing channel and, as a consequence, all the
897	 * virtio channels will have been already marked NOT ready, causing any
898	 * outstanding message on any vqueue to be ignored by complete_cb: now
899	 * we can just stop processing buffers and destroy the vqueues.
900	 */
901	virtio_reset_device(vdev);
902	vdev->config->del_vqs(vdev);
903	/* Ensure scmi_vdev is visible as NULL */
904	smp_store_mb(scmi_vdev, NULL);
905}
906
907static int scmi_vio_validate(struct virtio_device *vdev)
908{
909#ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_VERSION1_COMPLIANCE
910	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
911		dev_err(&vdev->dev,
912			"device does not comply with spec version 1.x\n");
913		return -EINVAL;
914	}
915#endif
916	return 0;
917}
918
919static unsigned int features[] = {
920	VIRTIO_SCMI_F_P2A_CHANNELS,
921};
922
923static const struct virtio_device_id id_table[] = {
924	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
925	{ 0 }
926};
927MODULE_DEVICE_TABLE(virtio, id_table);
928
929static struct virtio_driver virtio_scmi_driver = {
930	.driver.name = "scmi-virtio",
931	.feature_table = features,
932	.feature_table_size = ARRAY_SIZE(features),
933	.id_table = id_table,
934	.probe = scmi_vio_probe,
935	.remove = scmi_vio_remove,
936	.validate = scmi_vio_validate,
937};
938
939module_virtio_driver(virtio_scmi_driver);
940
941MODULE_AUTHOR("Igor Skalkin <igor.skalkin@opensynergy.com>");
942MODULE_AUTHOR("Peter Hilber <peter.hilber@opensynergy.com>");
943MODULE_AUTHOR("Cristian Marussi <cristian.marussi@arm.com>");
944MODULE_DESCRIPTION("SCMI VirtIO Transport driver");
945MODULE_LICENSE("GPL");