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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /drivers/firmware/arm_scmi/virtio.c
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'drivers/firmware/arm_scmi/virtio.c')
-rw-r--r--drivers/firmware/arm_scmi/virtio.c941
1 files changed, 941 insertions, 0 deletions
diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
new file mode 100644
index 000000000..1db975c08
--- /dev/null
+++ b/drivers/firmware/arm_scmi/virtio.c
@@ -0,0 +1,941 @@
+// 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);
+
+ /*
+ * 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;
+ if (!vioch->is_rx && vioch->deferred_tx_wq)
+ /* Cannot be kicked anymore after this...*/
+ vioch->deferred_tx_wq = NULL;
+ spin_unlock_irqrestore(&vioch->lock, flags);
+
+ 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 void scmi_destroy_tx_workqueue(void *deferred_tx_wq)
+{
+ destroy_workqueue(deferred_tx_wq);
+}
+
+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) {
+ int ret;
+
+ 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;
+
+ ret = devm_add_action_or_reset(dev, scmi_destroy_tx_workqueue,
+ vioch->deferred_tx_wq);
+ if (ret)
+ return ret;
+
+ 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(dev, sizeof(*msg), GFP_KERNEL);
+ if (!msg)
+ return -ENOMEM;
+
+ if (tx) {
+ msg->request = devm_kzalloc(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(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;
+
+ /*
+ * Break device to inhibit further traffic flowing while shutting down
+ * the channels: doing it later holding vioch->lock creates unsafe
+ * locking dependency chains as reported by LOCKDEP.
+ */
+ virtio_break_device(vioch->vqueue->vdev);
+ 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),
+};