[PATCH v2 2/9] firmware: arm_scmi: Review virtio free_list handling

Cristian Marussi
2022-02-01T17:16:23Z

Add a new spinlock dedicated to the access of the TX free list and a couple
of helpers to get and put messages back and forth from the free_list.

Cc: Igor Skalkin <igor.skalkin@opensynergy.com>
Cc: Peter Hilber <peter.hilber@opensynergy.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
drivers/firmware/arm_scmi/virtio.c | 88 +++++++++++++++++++-----------
1 file changed, 57 insertions(+), 31 deletions(-)

diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
index 536e46eab462..22d5a632262f 100644
--- a/drivers/firmware/arm_scmi/virtio.c
+++ b/drivers/firmware/arm_scmi/virtio.c
@@ -40,20 +40,23 @@
*
* @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
* @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.
+ * @lock: Protects access to all members except users, free_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;
bool is_rx;
unsigned int max_msg;
- /* lock to protect access to all members except users. */
+ /* lock to protect access to all members except users, free_list */
spinlock_t lock;
struct completion *shutdown_done;
refcount_t users;
@@ -142,18 +145,49 @@ static void scmi_vio_channel_cleanup_sync(struct scmi_vio_channel *vioch)
"Timeout shutting down %s VQ.\n", vq_name);
}

+/* 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);
+
+ 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)
+{
+ 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);
+}
+
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 device *dev)
+ 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);

@@ -170,17 +204,17 @@ static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
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, vioch->cinfo->dev);
- } else {
- /* Here IRQs are assumed to be already disabled by the caller */
- spin_lock(&vioch->lock);
- list_add(&msg->list, &vioch->free_list);
- spin_unlock(&vioch->lock);
- }
+ if (vioch->is_rx)
+ scmi_vio_feed_vq_rx(vioch, msg);
+ else
+ scmi_virtio_put_free_msg(vioch, msg);
}

static void scmi_vio_complete_cb(struct virtqueue *vqueue)
@@ -295,7 +329,6 @@ static bool virtio_chan_available(struct device *dev, int idx)
static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
bool tx)
{
- unsigned long flags;
struct scmi_vio_channel *vioch;
int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
int i;
@@ -325,13 +358,7 @@ static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
if (!msg->input)
return -ENOMEM;

- if (tx) {
- spin_lock_irqsave(&vioch->lock, flags);
- list_add_tail(&msg->list, &vioch->free_list);
- spin_unlock_irqrestore(&vioch->lock, flags);
- } else {
- scmi_vio_feed_vq_rx(vioch, msg, cinfo->dev);
- }
+ scmi_finalize_message(vioch, msg);
}

scmi_vio_channel_ready(vioch, cinfo);
@@ -365,33 +392,31 @@ static int virtio_send_message(struct scmi_chan_info *cinfo,
if (!scmi_vio_channel_acquire(vioch))
return -EINVAL;

- spin_lock_irqsave(&vioch->lock, flags);
-
- if (list_empty(&vioch->free_list)) {
- spin_unlock_irqrestore(&vioch->lock, flags);
+ msg = scmi_virtio_get_free_msg(vioch);
+ if (!msg) {
scmi_vio_channel_release(vioch);
return -EBUSY;
}

- msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
- list_del(&msg->list);
-
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);
+
rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
- if (rc) {
- list_add(&msg->list, &vioch->free_list);
+ if (rc)
dev_err(vioch->cinfo->dev,
"failed to add to TX virtqueue (%d)\n", rc);
- } else {
+ else
virtqueue_kick(vioch->vqueue);
- }

spin_unlock_irqrestore(&vioch->lock, flags);

+ if (rc)
+ scmi_virtio_put_free_msg(vioch, msg);
+
scmi_vio_channel_release(vioch);

return rc;
@@ -468,6 +493,7 @@ static int scmi_vio_probe(struct virtio_device *vdev)
unsigned int sz;

spin_lock_init(&channels[i].lock);
+ spin_lock_init(&channels[i].free_lock);
INIT_LIST_HEAD(&channels[i].free_list);
channels[i].vqueue = vqs[i];

--
2.17.1