mirrors
/
linux-stable
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
1
0
Fork 0
Code Issues Releases Wiki Activity

firmware: arm_scmi: Add atomic mode support to virtio transport 

Add support for .mark_txdone and .poll_done transport operations to SCMI
VirtIO transport as pre-requisites to enable atomic operations.

Add a Kernel configuration option to enable SCMI VirtIO transport polling
and atomic mode for selected SCMI transactions while leaving it default
disabled.

Link: https://lore.kernel.org/r/20220217131234.50328-4-cristian.marussi@arm.com
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Igor Skalkin <igor.skalkin@opensynergy.com>
Cc: Peter Hilber <peter.hilber@opensynergy.com>
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
This commit is contained in:
Cristian Marussi 2022-02-17 13:12:29 +00:00 committed by Sudeep Holla
parent 9a1699bda0
commit 5a3b7185c4
3 changed files with 392 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
drivers/firmware/arm_scmi/Kconfig
View File

@ -118,6 +118,21 @@ config ARM_SCMI_TRANSPORT_VIRTIO_VERSION1_COMPLIANCE
the ones implemented by kvmtool) and let the core Kernel VirtIO layer
take care of the needed conversions, say N.
config ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE
bool "Enable atomic mode for SCMI VirtIO transport"
depends on ARM_SCMI_TRANSPORT_VIRTIO
help
Enable support of atomic operation for SCMI VirtIO based transport.
If you want the SCMI VirtIO based transport to operate in atomic
mode, avoiding any kind of sleeping behaviour for selected
transactions on the TX path, answer Y.
Enabling atomic mode operations allows any SCMI driver using this
transport to optionally ask for atomic SCMI transactions and operate
in atomic context too, at the price of using a number of busy-waiting
primitives all over instead. If unsure say N.
endif #ARM_SCMI_PROTOCOL
config ARM_SCMI_POWER_DOMAIN

6
drivers/firmware/arm_scmi/driver.c
View File

@ -648,7 +648,8 @@ static void scmi_handle_notification(struct scmi_chan_info *cinfo,
unpack_scmi_header(msg_hdr, &xfer->hdr);
if (priv)
xfer->priv = priv;
/* Ensure order between xfer->priv store and following ops */
smp_store_mb(xfer->priv, priv);
info->desc->ops->fetch_notification(cinfo, info->desc->max_msg_size,
xfer);
scmi_notify(cinfo->handle, xfer->hdr.protocol_id,
@ -680,7 +681,8 @@ static void scmi_handle_response(struct scmi_chan_info *cinfo,
xfer->rx.len = info->desc->max_msg_size;
if (priv)
xfer->priv = priv;
/* Ensure order between xfer->priv store and following ops */
smp_store_mb(xfer->priv, priv);
info->desc->ops->fetch_response(cinfo, xfer);
trace_scmi_rx_done(xfer->transfer_id, xfer->hdr.id,

392
drivers/firmware/arm_scmi/virtio.c
View File

@ -3,8 +3,8 @@
* Virtio Transport driver for Arm System Control and Management Interface
* (SCMI).
*
* Copyright (C) 2020-2021 OpenSynergy.
* Copyright (C) 2021 ARM Ltd.
* Copyright (C) 2020-2022 OpenSynergy.
* Copyright (C) 2021-2022 ARM Ltd.
*/
/**
@ -42,9 +42,14 @@
* @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.
* @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.
*/
@ -54,14 +59,29 @@ struct scmi_vio_channel {
/* 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 */
/*
* 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
*
@ -69,12 +89,23 @@ struct scmi_vio_channel {
* @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 */
@ -117,6 +148,7 @@ 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
@ -127,10 +159,19 @@ static void scmi_vio_channel_cleanup_sync(struct scmi_vio_channel *vioch)
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 */
@ -154,18 +195,34 @@ scmi_virtio_get_free_msg(struct scmi_vio_channel *vioch)
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;
}
/* Assumes to be called with vio channel acquired already */
static void scmi_virtio_put_free_msg(struct scmi_vio_channel *vioch,
struct scmi_vio_msg *msg)
static inline bool scmi_vio_msg_acquire(struct scmi_vio_msg *msg)
{
unsigned long flags;
return refcount_inc_not_zero(&msg->users);
}
spin_lock_irqsave(&vioch->free_lock, flags);
list_add_tail(&msg->list, &vioch->free_list);
spin_unlock_irqrestore(&vioch->free_lock, flags);
/* 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)
@ -206,7 +263,7 @@ static void scmi_finalize_message(struct scmi_vio_channel *vioch,
if (vioch->is_rx)
scmi_vio_feed_vq_rx(vioch, msg);
else
scmi_virtio_put_free_msg(vioch, msg);
scmi_vio_msg_release(vioch, msg);
}
static void scmi_vio_complete_cb(struct virtqueue *vqueue)
@ -230,6 +287,7 @@ static void scmi_vio_complete_cb(struct virtqueue *vqueue)
virtqueue_disable_cb(vqueue);
cb_enabled = false;
}
msg = virtqueue_get_buf(vqueue, &length);
if (!msg) {
if (virtqueue_enable_cb(vqueue)) {
@ -260,6 +318,49 @@ static void scmi_vio_complete_cb(struct virtqueue *vqueue)
}
}
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[] = {
@ -327,6 +428,19 @@ static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
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;
@ -340,6 +454,8 @@ static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
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,
@ -394,6 +510,21 @@ static int virtio_send_message(struct scmi_chan_info *cinfo,
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,
@ -403,8 +534,13 @@ static int virtio_send_message(struct scmi_chan_info *cinfo,
spin_unlock_irqrestore(&vioch->lock, flags);
if (rc)
scmi_virtio_put_free_msg(vioch, msg);
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);
@ -416,10 +552,8 @@ static void virtio_fetch_response(struct scmi_chan_info *cinfo,
{
struct scmi_vio_msg *msg = xfer->priv;
if (msg) {
if (msg)
msg_fetch_response(msg->input, msg->rx_len, xfer);
xfer->priv = NULL;
}
}
static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
@ -427,10 +561,225 @@ static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
{
struct scmi_vio_msg *msg = xfer->priv;
if (msg) {
if (msg)
msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
xfer->priv = NULL;
}
/**
* 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 = {
@ -442,6 +791,8 @@ static const struct scmi_transport_ops scmi_virtio_ops = {
.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)
@ -484,6 +835,8 @@ static int scmi_vio_probe(struct virtio_device *vdev)
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);
@ -573,4 +926,5 @@ const struct scmi_desc scmi_virtio_desc = {
.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),
};