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