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