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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Virtio Transport driver for Arm System Control and Management Interface
  * (SCMI).
  *
  * Copyright (C) 2020-2022 OpenSynergy.
  * Copyright (C) 2021-2022 ARM Ltd.
  */
 
 /**
  * DOC: Theory of Operation
  *
  * The scmi-virtio transport implements a driver for the virtio SCMI device.
  *
  * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
  * channel (virtio eventq, P2A channel). Each channel is implemented through a
  * virtqueue. Access to each virtqueue is protected by spinlocks.
  */
 
 #include <linux/completion.h>
 #include <linux/errno.h>
 #include <linux/refcount.h>
 #include <linux/slab.h>
 #include <linux/virtio.h>
 #include <linux/virtio_config.h>
 
 #include <uapi/linux/virtio_ids.h>
 #include <uapi/linux/virtio_scmi.h>
 
 #include "common.h"
 
 #define VIRTIO_MAX_RX_TIMEOUT_MS    60000
 #define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
 #define VIRTIO_SCMI_MAX_PDU_SIZE \
     (VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
 #define DESCRIPTORS_PER_TX_MSG 2
 
 /**
  * struct scmi_vio_channel - Transport channel information
  *
  * @vqueue: Associated virtqueue
  * @cinfo: SCMI Tx or Rx channel
  * @free_lock: Protects access to the @free_list.
  * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
  * @deferred_tx_work: Worker for TX deferred replies processing
  * @deferred_tx_wq: Workqueue for TX deferred replies
  * @pending_lock: Protects access to the @pending_cmds_list.
  * @pending_cmds_list: List of pre-fetched commands queueud for later processing
  * @is_rx: Whether channel is an Rx channel
  * @max_msg: Maximum number of pending messages for this channel.
  * @lock: Protects access to all members except users, free_list and
  *    pending_cmds_list.
  * @shutdown_done: A reference to a completion used when freeing this channel.
  * @users: A reference count to currently active users of this channel.
  */
 struct scmi_vio_channel {
     struct virtqueue *vqueue;
     struct scmi_chan_info *cinfo;
     /* lock to protect access to the free list. */
     spinlock_t free_lock;
     struct list_head free_list;
     /* lock to protect access to the pending list. */
     spinlock_t pending_lock;
     struct list_head pending_cmds_list;
     struct work_struct deferred_tx_work;
     struct workqueue_struct *deferred_tx_wq;
     bool is_rx;
     unsigned int max_msg;
     /*
      * Lock to protect access to all members except users, free_list and
      * pending_cmds_list
      */
     spinlock_t lock;
     struct completion *shutdown_done;
     refcount_t users;
 };
 
 enum poll_states {
     VIO_MSG_NOT_POLLED,
     VIO_MSG_POLL_TIMEOUT,
     VIO_MSG_POLLING,
     VIO_MSG_POLL_DONE,
 };
 
 /**
  * struct scmi_vio_msg - Transport PDU information
  *
  * @request: SDU used for commands
  * @input: SDU used for (delayed) responses and notifications
  * @list: List which scmi_vio_msg may be part of
  * @rx_len: Input SDU size in bytes, once input has been received
  * @poll_idx: Last used index registered for polling purposes if this message
  *        transaction reply was configured for polling.
  * @poll_status: Polling state for this message.
  * @poll_lock: A lock to protect @poll_status
  * @users: A reference count to track this message users and avoid premature
  *     freeing (and reuse) when polling and IRQ execution paths interleave.
  */
 struct scmi_vio_msg {
     struct scmi_msg_payld *request;
     struct scmi_msg_payld *input;
     struct list_head list;
     unsigned int rx_len;
     unsigned int poll_idx;
     enum poll_states poll_status;
     /* Lock to protect access to poll_status */
     spinlock_t poll_lock;
     refcount_t users;
 };
 
 /* Only one SCMI VirtIO device can possibly exist */
 static struct virtio_device *scmi_vdev;
 
 static void scmi_vio_channel_ready(struct scmi_vio_channel *vioch,
                    struct scmi_chan_info *cinfo)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&vioch->lock, flags);
     cinfo->transport_info = vioch;
     /* Indirectly setting channel not available any more */
     vioch->cinfo = cinfo;
     spin_unlock_irqrestore(&vioch->lock, flags);
 
     refcount_set(&vioch->users, 1);
 }
 
 static inline bool scmi_vio_channel_acquire(struct scmi_vio_channel *vioch)
 {
     return refcount_inc_not_zero(&vioch->users);
 }
 
 static inline void scmi_vio_channel_release(struct scmi_vio_channel *vioch)
 {
     if (refcount_dec_and_test(&vioch->users)) {
         unsigned long flags;
 
         spin_lock_irqsave(&vioch->lock, flags);
         if (vioch->shutdown_done) {
             vioch->cinfo = NULL;
             complete(vioch->shutdown_done);
         }
         spin_unlock_irqrestore(&vioch->lock, flags);
     }
 }
 
 static void scmi_vio_channel_cleanup_sync(struct scmi_vio_channel *vioch)
 {
     unsigned long flags;
     DECLARE_COMPLETION_ONSTACK(vioch_shutdown_done);
     void *deferred_wq = NULL;
 
     /*
      * Prepare to wait for the last release if not already released
      * or in progress.
      */
     spin_lock_irqsave(&vioch->lock, flags);
     if (!vioch->cinfo || vioch->shutdown_done) {
         spin_unlock_irqrestore(&vioch->lock, flags);
         return;
     }
 
     vioch->shutdown_done = &vioch_shutdown_done;
     virtio_break_device(vioch->vqueue->vdev);
     if (!vioch->is_rx && vioch->deferred_tx_wq) {
         deferred_wq = vioch->deferred_tx_wq;
         /* Cannot be kicked anymore after this...*/
         vioch->deferred_tx_wq = NULL;
     }
     spin_unlock_irqrestore(&vioch->lock, flags);
 
     if (deferred_wq)
         destroy_workqueue(deferred_wq);
 
     scmi_vio_channel_release(vioch);
 
     /* Let any possibly concurrent RX path release the channel */
     wait_for_completion(vioch->shutdown_done);
 }
 
 /* Assumes to be called with vio channel acquired already */
 static struct scmi_vio_msg *
 scmi_virtio_get_free_msg(struct scmi_vio_channel *vioch)
 {
     unsigned long flags;
     struct scmi_vio_msg *msg;
 
     spin_lock_irqsave(&vioch->free_lock, flags);
     if (list_empty(&vioch->free_list)) {
         spin_unlock_irqrestore(&vioch->free_lock, flags);
         return NULL;
     }
 
     msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
     list_del_init(&msg->list);
     spin_unlock_irqrestore(&vioch->free_lock, flags);
 
     /* Still no users, no need to acquire poll_lock */
     msg->poll_status = VIO_MSG_NOT_POLLED;
     refcount_set(&msg->users, 1);
 
     return msg;
 }
 
 static inline bool scmi_vio_msg_acquire(struct scmi_vio_msg *msg)
 {
     return refcount_inc_not_zero(&msg->users);
 }
 
 /* Assumes to be called with vio channel acquired already */
 static inline bool scmi_vio_msg_release(struct scmi_vio_channel *vioch,
                     struct scmi_vio_msg *msg)
 {
     bool ret;
 
     ret = refcount_dec_and_test(&msg->users);
     if (ret) {
         unsigned long flags;
 
         spin_lock_irqsave(&vioch->free_lock, flags);
         list_add_tail(&msg->list, &vioch->free_list);
         spin_unlock_irqrestore(&vioch->free_lock, flags);
     }
 
     return ret;
 }
 
 static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
 {
     return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
 }
 
 static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
                    struct scmi_vio_msg *msg)
 {
     struct scatterlist sg_in;
     int rc;
     unsigned long flags;
     struct device *dev = &vioch->vqueue->vdev->dev;
 
     sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
 
     spin_lock_irqsave(&vioch->lock, flags);
 
     rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
     if (rc)
         dev_err(dev, "failed to add to RX virtqueue (%d)\n", rc);
     else
         virtqueue_kick(vioch->vqueue);
 
     spin_unlock_irqrestore(&vioch->lock, flags);
 
     return rc;
 }
 
 /*
  * Assume to be called with channel already acquired or not ready at all;
  * vioch->lock MUST NOT have been already acquired.
  */
 static void scmi_finalize_message(struct scmi_vio_channel *vioch,
                   struct scmi_vio_msg *msg)
 {
     if (vioch->is_rx)
         scmi_vio_feed_vq_rx(vioch, msg);
     else
         scmi_vio_msg_release(vioch, msg);
 }
 
 static void scmi_vio_complete_cb(struct virtqueue *vqueue)
 {
     unsigned long flags;
     unsigned int length;
     struct scmi_vio_channel *vioch;
     struct scmi_vio_msg *msg;
     bool cb_enabled = true;
 
     if (WARN_ON_ONCE(!vqueue->vdev->priv))
         return;
     vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
 
     for (;;) {
         if (!scmi_vio_channel_acquire(vioch))
             return;
 
         spin_lock_irqsave(&vioch->lock, flags);
         if (cb_enabled) {
             virtqueue_disable_cb(vqueue);
             cb_enabled = false;
         }
 
         msg = virtqueue_get_buf(vqueue, &length);
         if (!msg) {
             if (virtqueue_enable_cb(vqueue)) {
                 spin_unlock_irqrestore(&vioch->lock, flags);
                 scmi_vio_channel_release(vioch);
                 return;
             }
             cb_enabled = true;
         }
         spin_unlock_irqrestore(&vioch->lock, flags);
 
         if (msg) {
             msg->rx_len = length;
             scmi_rx_callback(vioch->cinfo,
                      msg_read_header(msg->input), msg);
 
             scmi_finalize_message(vioch, msg);
         }
 
         /*
          * Release vio channel between loop iterations to allow
          * virtio_chan_free() to eventually fully release it when
          * shutting down; in such a case, any outstanding message will
          * be ignored since this loop will bail out at the next
          * iteration.
          */
         scmi_vio_channel_release(vioch);
     }
 }
 
 static void scmi_vio_deferred_tx_worker(struct work_struct *work)
 {
     unsigned long flags;
     struct scmi_vio_channel *vioch;
     struct scmi_vio_msg *msg, *tmp;
 
     vioch = container_of(work, struct scmi_vio_channel, deferred_tx_work);
 
     if (!scmi_vio_channel_acquire(vioch))
         return;
 
     /*
      * Process pre-fetched messages: these could be non-polled messages or
      * late timed-out replies to polled messages dequeued by chance while
      * polling for some other messages: this worker is in charge to process
      * the valid non-expired messages and anyway finally free all of them.
      */
     spin_lock_irqsave(&vioch->pending_lock, flags);
 
     /* Scan the list of possibly pre-fetched messages during polling. */
     list_for_each_entry_safe(msg, tmp, &vioch->pending_cmds_list, list) {
         list_del(&msg->list);
 
         /*
          * Channel is acquired here (cannot vanish) and this message
          * is no more processed elsewhere so no poll_lock needed.
          */
         if (msg->poll_status == VIO_MSG_NOT_POLLED)
             scmi_rx_callback(vioch->cinfo,
                      msg_read_header(msg->input), msg);
 
         /* Free the processed message once done */
         scmi_vio_msg_release(vioch, msg);
     }
 
     spin_unlock_irqrestore(&vioch->pending_lock, flags);
 
     /* Process possibly still pending messages */
     scmi_vio_complete_cb(vioch->vqueue);
 
     scmi_vio_channel_release(vioch);
 }
 
 static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
 
 static vq_callback_t *scmi_vio_complete_callbacks[] = {
     scmi_vio_complete_cb,
     scmi_vio_complete_cb
 };
 
 static unsigned int virtio_get_max_msg(struct scmi_chan_info *base_cinfo)
 {
     struct scmi_vio_channel *vioch = base_cinfo->transport_info;
 
     return vioch->max_msg;
 }
 
 static int virtio_link_supplier(struct device *dev)
 {
     if (!scmi_vdev) {
         dev_notice(dev,
                "Deferring probe after not finding a bound scmi-virtio device\n");
         return -EPROBE_DEFER;
     }
 
     if (!device_link_add(dev, &scmi_vdev->dev,
                  DL_FLAG_AUTOREMOVE_CONSUMER)) {
         dev_err(dev, "Adding link to supplier virtio device failed\n");
         return -ECANCELED;
     }
 
     return 0;
 }
 
 static bool virtio_chan_available(struct device *dev, int idx)
 {
     struct scmi_vio_channel *channels, *vioch = NULL;
 
     if (WARN_ON_ONCE(!scmi_vdev))
         return false;
 
     channels = (struct scmi_vio_channel *)scmi_vdev->priv;
 
     switch (idx) {
     case VIRTIO_SCMI_VQ_TX:
         vioch = &channels[VIRTIO_SCMI_VQ_TX];
         break;
     case VIRTIO_SCMI_VQ_RX:
         if (scmi_vio_have_vq_rx(scmi_vdev))
             vioch = &channels[VIRTIO_SCMI_VQ_RX];
         break;
     default:
         return false;
     }
 
     return vioch && !vioch->cinfo;
 }
 
 static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
                  bool tx)
 {
     struct scmi_vio_channel *vioch;
     int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
     int i;
 
     if (!scmi_vdev)
         return -EPROBE_DEFER;
 
     vioch = &((struct scmi_vio_channel *)scmi_vdev->priv)[index];
 
     /* Setup a deferred worker for polling. */
     if (tx && !vioch->deferred_tx_wq) {
         vioch->deferred_tx_wq =
             alloc_workqueue(dev_name(&scmi_vdev->dev),
                     WQ_UNBOUND | WQ_FREEZABLE | WQ_SYSFS,
                     0);
         if (!vioch->deferred_tx_wq)
             return -ENOMEM;
 
         INIT_WORK(&vioch->deferred_tx_work,
               scmi_vio_deferred_tx_worker);
     }
 
     for (i = 0; i < vioch->max_msg; i++) {
         struct scmi_vio_msg *msg;
 
         msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
         if (!msg)
             return -ENOMEM;
 
         if (tx) {
             msg->request = devm_kzalloc(cinfo->dev,
                             VIRTIO_SCMI_MAX_PDU_SIZE,
                             GFP_KERNEL);
             if (!msg->request)
                 return -ENOMEM;
             spin_lock_init(&msg->poll_lock);
             refcount_set(&msg->users, 1);
         }
 
         msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
                       GFP_KERNEL);
         if (!msg->input)
             return -ENOMEM;
 
         scmi_finalize_message(vioch, msg);
     }
 
     scmi_vio_channel_ready(vioch, cinfo);
 
     return 0;
 }
 
 static int virtio_chan_free(int id, void *p, void *data)
 {
     struct scmi_chan_info *cinfo = p;
     struct scmi_vio_channel *vioch = cinfo->transport_info;
 
     scmi_vio_channel_cleanup_sync(vioch);
 
     scmi_free_channel(cinfo, data, id);
 
     return 0;
 }
 
 static int virtio_send_message(struct scmi_chan_info *cinfo,
                    struct scmi_xfer *xfer)
 {
     struct scmi_vio_channel *vioch = cinfo->transport_info;
     struct scatterlist sg_out;
     struct scatterlist sg_in;
     struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
     unsigned long flags;
     int rc;
     struct scmi_vio_msg *msg;
 
     if (!scmi_vio_channel_acquire(vioch))
         return -EINVAL;
 
     msg = scmi_virtio_get_free_msg(vioch);
     if (!msg) {
         scmi_vio_channel_release(vioch);
         return -EBUSY;
     }
 
     msg_tx_prepare(msg->request, xfer);
 
     sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
     sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
 
     spin_lock_irqsave(&vioch->lock, flags);
 
     /*
      * If polling was requested for this transaction:
      *  - retrieve last used index (will be used as polling reference)
      *  - bind the polled message to the xfer via .priv
      *  - grab an additional msg refcount for the poll-path
      */
     if (xfer->hdr.poll_completion) {
         msg->poll_idx = virtqueue_enable_cb_prepare(vioch->vqueue);
         /* Still no users, no need to acquire poll_lock */
         msg->poll_status = VIO_MSG_POLLING;
         scmi_vio_msg_acquire(msg);
         /* Ensure initialized msg is visibly bound to xfer */
         smp_store_mb(xfer->priv, msg);
     }
 
     rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
     if (rc)
         dev_err(vioch->cinfo->dev,
             "failed to add to TX virtqueue (%d)\n", rc);
     else
         virtqueue_kick(vioch->vqueue);
 
     spin_unlock_irqrestore(&vioch->lock, flags);
 
     if (rc) {
         /* Ensure order between xfer->priv clear and vq feeding */
         smp_store_mb(xfer->priv, NULL);
         if (xfer->hdr.poll_completion)
             scmi_vio_msg_release(vioch, msg);
         scmi_vio_msg_release(vioch, msg);
     }
 
     scmi_vio_channel_release(vioch);
 
     return rc;
 }
 
 static void virtio_fetch_response(struct scmi_chan_info *cinfo,
                   struct scmi_xfer *xfer)
 {
     struct scmi_vio_msg *msg = xfer->priv;
 
     if (msg)
         msg_fetch_response(msg->input, msg->rx_len, xfer);
 }
 
 static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
                       size_t max_len, struct scmi_xfer *xfer)
 {
     struct scmi_vio_msg *msg = xfer->priv;
 
     if (msg)
         msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
 }
 
 /**
  * virtio_mark_txdone  - Mark transmission done
  *
  * Free only completed polling transfer messages.
  *
  * Note that in the SCMI VirtIO transport we never explicitly release still
  * outstanding but timed-out messages by forcibly re-adding them to the
  * free-list inside the TX code path; we instead let IRQ/RX callbacks, or the
  * TX deferred worker, eventually clean up such messages once, finally, a late
  * reply is received and discarded (if ever).
  *
  * This approach was deemed preferable since those pending timed-out buffers are
  * still effectively owned by the SCMI platform VirtIO device even after timeout
  * expiration: forcibly freeing and reusing them before they had been returned
  * explicitly by the SCMI platform could lead to subtle bugs due to message
  * corruption.
  * An SCMI platform VirtIO device which never returns message buffers is
  * anyway broken and it will quickly lead to exhaustion of available messages.
  *
  * For this same reason, here, we take care to free only the polled messages
  * that had been somehow replied (only if not by chance already processed on the
  * IRQ path - the initial scmi_vio_msg_release() takes care of this) and also
  * any timed-out polled message if that indeed appears to have been at least
  * dequeued from the virtqueues (VIO_MSG_POLL_DONE): this is needed since such
  * messages won't be freed elsewhere. Any other polled message is marked as
  * VIO_MSG_POLL_TIMEOUT.
  *
  * Possible late replies to timed-out polled messages will be eventually freed
  * by RX callbacks if delivered on the IRQ path or by the deferred TX worker if
  * dequeued on some other polling path.
  *
  * @cinfo: SCMI channel info
  * @ret: Transmission return code
  * @xfer: Transfer descriptor
  */
 static void virtio_mark_txdone(struct scmi_chan_info *cinfo, int ret,
                    struct scmi_xfer *xfer)
 {
     unsigned long flags;
     struct scmi_vio_channel *vioch = cinfo->transport_info;
     struct scmi_vio_msg *msg = xfer->priv;
 
     if (!msg || !scmi_vio_channel_acquire(vioch))
         return;
 
     /* Ensure msg is unbound from xfer anyway at this point */
     smp_store_mb(xfer->priv, NULL);
 
     /* Must be a polled xfer and not already freed on the IRQ path */
     if (!xfer->hdr.poll_completion || scmi_vio_msg_release(vioch, msg)) {
         scmi_vio_channel_release(vioch);
         return;
     }
 
     spin_lock_irqsave(&msg->poll_lock, flags);
     /* Do not free timedout polled messages only if still inflight */
     if (ret != -ETIMEDOUT || msg->poll_status == VIO_MSG_POLL_DONE)
         scmi_vio_msg_release(vioch, msg);
     else if (msg->poll_status == VIO_MSG_POLLING)
         msg->poll_status = VIO_MSG_POLL_TIMEOUT;
     spin_unlock_irqrestore(&msg->poll_lock, flags);
 
     scmi_vio_channel_release(vioch);
 }
 
 /**
  * virtio_poll_done  - Provide polling support for VirtIO transport
  *
  * @cinfo: SCMI channel info
  * @xfer: Reference to the transfer being poll for.
  *
  * VirtIO core provides a polling mechanism based only on last used indexes:
  * this means that it is possible to poll the virtqueues waiting for something
  * new to arrive from the host side, but the only way to check if the freshly
  * arrived buffer was indeed what we were waiting for is to compare the newly
  * arrived message descriptor with the one we are polling on.
  *
  * As a consequence it can happen to dequeue something different from the buffer
  * we were poll-waiting for: if that is the case such early fetched buffers are
  * then added to a the @pending_cmds_list list for later processing by a
  * dedicated deferred worker.
  *
  * So, basically, once something new is spotted we proceed to de-queue all the
  * freshly received used buffers until we found the one we were polling on, or,
  * we have 'seemingly' emptied the virtqueue; if some buffers are still pending
  * in the vqueue at the end of the polling loop (possible due to inherent races
  * in virtqueues handling mechanisms), we similarly kick the deferred worker
  * and let it process those, to avoid indefinitely looping in the .poll_done
  * busy-waiting helper.
  *
  * Finally, we delegate to the deferred worker also the final free of any timed
  * out reply to a polled message that we should dequeue.
  *
  * Note that, since we do NOT have per-message suppress notification mechanism,
  * the message we are polling for could be alternatively delivered via usual
  * IRQs callbacks on another core which happened to have IRQs enabled while we
  * are actively polling for it here: in such a case it will be handled as such
  * by scmi_rx_callback() and the polling loop in the SCMI Core TX path will be
  * transparently terminated anyway.
  *
  * Return: True once polling has successfully completed.
  */
 static bool virtio_poll_done(struct scmi_chan_info *cinfo,
                  struct scmi_xfer *xfer)
 {
     bool pending, found = false;
     unsigned int length, any_prefetched = 0;
     unsigned long flags;
     struct scmi_vio_msg *next_msg, *msg = xfer->priv;
     struct scmi_vio_channel *vioch = cinfo->transport_info;
 
     if (!msg)
         return true;
 
     /*
      * Processed already by other polling loop on another CPU ?
      *
      * Note that this message is acquired on the poll path so cannot vanish
      * while inside this loop iteration even if concurrently processed on
      * the IRQ path.
      *
      * Avoid to acquire poll_lock since polled_status can be changed
      * in a relevant manner only later in this same thread of execution:
      * any other possible changes made concurrently by other polling loops
      * or by a reply delivered on the IRQ path have no meaningful impact on
      * this loop iteration: in other words it is harmless to allow this
      * possible race but let has avoid spinlocking with irqs off in this
      * initial part of the polling loop.
      */
     if (msg->poll_status == VIO_MSG_POLL_DONE)
         return true;
 
     if (!scmi_vio_channel_acquire(vioch))
         return true;
 
     /* Has cmdq index moved at all ? */
     pending = virtqueue_poll(vioch->vqueue, msg->poll_idx);
     if (!pending) {
         scmi_vio_channel_release(vioch);
         return false;
     }
 
     spin_lock_irqsave(&vioch->lock, flags);
     virtqueue_disable_cb(vioch->vqueue);
 
     /*
      * Process all new messages till the polled-for message is found OR
      * the vqueue is empty.
      */
     while ((next_msg = virtqueue_get_buf(vioch->vqueue, &length))) {
         bool next_msg_done = false;
 
         /*
          * Mark any dequeued buffer message as VIO_MSG_POLL_DONE so
          * that can be properly freed even on timeout in mark_txdone.
          */
         spin_lock(&next_msg->poll_lock);
         if (next_msg->poll_status == VIO_MSG_POLLING) {
             next_msg->poll_status = VIO_MSG_POLL_DONE;
             next_msg_done = true;
         }
         spin_unlock(&next_msg->poll_lock);
 
         next_msg->rx_len = length;
         /* Is the message we were polling for ? */
         if (next_msg == msg) {
             found = true;
             break;
         } else if (next_msg_done) {
             /* Skip the rest if this was another polled msg */
             continue;
         }
 
         /*
          * Enqueue for later processing any non-polled message and any
          * timed-out polled one that we happen to have dequeued.
          */
         spin_lock(&next_msg->poll_lock);
         if (next_msg->poll_status == VIO_MSG_NOT_POLLED ||
             next_msg->poll_status == VIO_MSG_POLL_TIMEOUT) {
             spin_unlock(&next_msg->poll_lock);
 
             any_prefetched++;
             spin_lock(&vioch->pending_lock);
             list_add_tail(&next_msg->list,
                       &vioch->pending_cmds_list);
             spin_unlock(&vioch->pending_lock);
         } else {
             spin_unlock(&next_msg->poll_lock);
         }
     }
 
     /*
      * When the polling loop has successfully terminated if something
      * else was queued in the meantime, it will be served by a deferred
      * worker OR by the normal IRQ/callback OR by other poll loops.
      *
      * If we are still looking for the polled reply, the polling index has
      * to be updated to the current vqueue last used index.
      */
     if (found) {
         pending = !virtqueue_enable_cb(vioch->vqueue);
     } else {
         msg->poll_idx = virtqueue_enable_cb_prepare(vioch->vqueue);
         pending = virtqueue_poll(vioch->vqueue, msg->poll_idx);
     }
 
     if (vioch->deferred_tx_wq && (any_prefetched || pending))
         queue_work(vioch->deferred_tx_wq, &vioch->deferred_tx_work);
 
     spin_unlock_irqrestore(&vioch->lock, flags);
 
     scmi_vio_channel_release(vioch);
 
     return found;
 }
 
 static const struct scmi_transport_ops scmi_virtio_ops = {
     .link_supplier = virtio_link_supplier,
     .chan_available = virtio_chan_available,
     .chan_setup = virtio_chan_setup,
     .chan_free = virtio_chan_free,
     .get_max_msg = virtio_get_max_msg,
     .send_message = virtio_send_message,
     .fetch_response = virtio_fetch_response,
     .fetch_notification = virtio_fetch_notification,
     .mark_txdone = virtio_mark_txdone,
     .poll_done = virtio_poll_done,
 };
 
 static int scmi_vio_probe(struct virtio_device *vdev)
 {
     struct device *dev = &vdev->dev;
     struct scmi_vio_channel *channels;
     bool have_vq_rx;
     int vq_cnt;
     int i;
     int ret;
     struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
 
     /* Only one SCMI VirtiO device allowed */
     if (scmi_vdev) {
         dev_err(dev,
             "One SCMI Virtio device was already initialized: only one allowed.\n");
         return -EBUSY;
     }
 
     have_vq_rx = scmi_vio_have_vq_rx(vdev);
     vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
 
     channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
     if (!channels)
         return -ENOMEM;
 
     if (have_vq_rx)
         channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
 
     ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
                   scmi_vio_vqueue_names, NULL);
     if (ret) {
         dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
         return ret;
     }
 
     for (i = 0; i < vq_cnt; i++) {
         unsigned int sz;
 
         spin_lock_init(&channels[i].lock);
         spin_lock_init(&channels[i].free_lock);
         INIT_LIST_HEAD(&channels[i].free_list);
         spin_lock_init(&channels[i].pending_lock);
         INIT_LIST_HEAD(&channels[i].pending_cmds_list);
         channels[i].vqueue = vqs[i];
 
         sz = virtqueue_get_vring_size(channels[i].vqueue);
         /* Tx messages need multiple descriptors. */
         if (!channels[i].is_rx)
             sz /= DESCRIPTORS_PER_TX_MSG;
 
         if (sz > MSG_TOKEN_MAX) {
             dev_info(dev,
                  "%s virtqueue could hold %d messages. Only %ld allowed to be pending.\n",
                  channels[i].is_rx ? "rx" : "tx",
                  sz, MSG_TOKEN_MAX);
             sz = MSG_TOKEN_MAX;
         }
         channels[i].max_msg = sz;
     }
 
     vdev->priv = channels;
     /* Ensure initialized scmi_vdev is visible */
     smp_store_mb(scmi_vdev, vdev);
 
     return 0;
 }
 
 static void scmi_vio_remove(struct virtio_device *vdev)
 {
     /*
      * Once we get here, virtio_chan_free() will have already been called by
      * the SCMI core for any existing channel and, as a consequence, all the
      * virtio channels will have been already marked NOT ready, causing any
      * outstanding message on any vqueue to be ignored by complete_cb: now
      * we can just stop processing buffers and destroy the vqueues.
      */
     virtio_reset_device(vdev);
     vdev->config->del_vqs(vdev);
     /* Ensure scmi_vdev is visible as NULL */
     smp_store_mb(scmi_vdev, NULL);
 }
 
 static int scmi_vio_validate(struct virtio_device *vdev)
 {
 #ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_VERSION1_COMPLIANCE
     if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
         dev_err(&vdev->dev,
             "device does not comply with spec version 1.x\n");
         return -EINVAL;
     }
 #endif
     return 0;
 }
 
 static unsigned int features[] = {
     VIRTIO_SCMI_F_P2A_CHANNELS,
 };
 
 static const struct virtio_device_id id_table[] = {
     { VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
     { 0 }
 };
 
 static struct virtio_driver virtio_scmi_driver = {
     .driver.name = "scmi-virtio",
     .driver.owner = THIS_MODULE,
     .feature_table = features,
     .feature_table_size = ARRAY_SIZE(features),
     .id_table = id_table,
     .probe = scmi_vio_probe,
     .remove = scmi_vio_remove,
     .validate = scmi_vio_validate,
 };
 
 static int __init virtio_scmi_init(void)
 {
     return register_virtio_driver(&virtio_scmi_driver);
 }
 
 static void virtio_scmi_exit(void)
 {
     unregister_virtio_driver(&virtio_scmi_driver);
 }
 
 const struct scmi_desc scmi_virtio_desc = {
     .transport_init = virtio_scmi_init,
     .transport_exit = virtio_scmi_exit,
     .ops = &scmi_virtio_ops,
     /* for non-realtime virtio devices */
     .max_rx_timeout_ms = VIRTIO_MAX_RX_TIMEOUT_MS,
     .max_msg = 0, /* overridden by virtio_get_max_msg() */
     .max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
     .atomic_enabled = IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE),
 };

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