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rpmsg: virtio: EPOLLOUT support

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Previously, polling an rpmsg endpoint (e.g. /dev/ttyRPMSGx) would
generate EPOLLIN events but no EPOLLOUT events.

Unfortunately, poll support means that we can no longer disable
tx-complete interrupts as there is no way to know whether a poller is
waiting in sendq, so we always need notifications.

Signed-off-by: Patrick Oppenlander <patrick.oppenlander@gmail.com>
Link: https://lore.kernel.org/r/20251022032817.320378-1-patrick.oppenlander@gmail.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
This commit is contained in:
Patrick Oppenlander
2025-10-22 14:28:17 +11:00
committed by Mathieu Poirier
parent 8f0b4cce44
commit c38d8b66c8
1 changed files with 32 additions and 69 deletions
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101
drivers/rpmsg/virtio_rpmsg_bus.c
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@@ -41,13 +41,12 @@
* @buf_size: size of one rx or tx buffer
* @last_sbuf: index of last tx buffer used
* @bufs_dma: dma base addr of the buffers
* @tx_lock: protects svq, sbufs and sleepers, to allow concurrent senders.
* @tx_lock: protects svq and sbufs, to allow concurrent senders.
* sending a message might require waking up a dozing remote
* processor, which involves sleeping, hence the mutex.
* @endpoints: idr of local endpoints, allows fast retrieval
* @endpoints_lock: lock of the endpoints set
* @sendq: wait queue of sending contexts waiting for a tx buffers
* @sleepers: number of senders that are waiting for a tx buffer
*
* This structure stores the rpmsg state of a given virtio remote processor
* device (there might be several virtio proc devices for each physical
@@ -65,7 +64,6 @@ struct virtproc_info {
struct idr endpoints;
struct mutex endpoints_lock;
wait_queue_head_t sendq;
atomic_t sleepers;
};
/* The feature bitmap for virtio rpmsg */
@@ -144,6 +142,8 @@ static int virtio_rpmsg_sendto(struct rpmsg_endpoint *ept, void *data, int len,
static int virtio_rpmsg_trysend(struct rpmsg_endpoint *ept, void *data, int len);
static int virtio_rpmsg_trysendto(struct rpmsg_endpoint *ept, void *data,
int len, u32 dst);
static __poll_t virtio_rpmsg_poll(struct rpmsg_endpoint *ept, struct file *filp,
poll_table *wait);
static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept);
static struct rpmsg_device *__rpmsg_create_channel(struct virtproc_info *vrp,
struct rpmsg_channel_info *chinfo);
@@ -154,6 +154,7 @@ static const struct rpmsg_endpoint_ops virtio_endpoint_ops = {
.sendto = virtio_rpmsg_sendto,
.trysend = virtio_rpmsg_trysend,
.trysendto = virtio_rpmsg_trysendto,
.poll = virtio_rpmsg_poll,
.get_mtu = virtio_rpmsg_get_mtu,
};
@@ -436,7 +437,6 @@ static void *get_a_tx_buf(struct virtproc_info *vrp)
unsigned int len;
void *ret;
/* support multiple concurrent senders */
mutex_lock(&vrp->tx_lock);
/*
@@ -454,62 +454,6 @@ static void *get_a_tx_buf(struct virtproc_info *vrp)
return ret;
}
/**
* rpmsg_upref_sleepers() - enable "tx-complete" interrupts, if needed
* @vrp: virtual remote processor state
*
* This function is called before a sender is blocked, waiting for
* a tx buffer to become available.
*
* If we already have blocking senders, this function merely increases
* the "sleepers" reference count, and exits.
*
* Otherwise, if this is the first sender to block, we also enable
* virtio's tx callbacks, so we'd be immediately notified when a tx
* buffer is consumed (we rely on virtio's tx callback in order
* to wake up sleeping senders as soon as a tx buffer is used by the
* remote processor).
*/
static void rpmsg_upref_sleepers(struct virtproc_info *vrp)
{
/* support multiple concurrent senders */
mutex_lock(&vrp->tx_lock);
/* are we the first sleeping context waiting for tx buffers ? */
if (atomic_inc_return(&vrp->sleepers) == 1)
/* enable "tx-complete" interrupts before dozing off */
virtqueue_enable_cb(vrp->svq);
mutex_unlock(&vrp->tx_lock);
}
/**
* rpmsg_downref_sleepers() - disable "tx-complete" interrupts, if needed
* @vrp: virtual remote processor state
*
* This function is called after a sender, that waited for a tx buffer
* to become available, is unblocked.
*
* If we still have blocking senders, this function merely decreases
* the "sleepers" reference count, and exits.
*
* Otherwise, if there are no more blocking senders, we also disable
* virtio's tx callbacks, to avoid the overhead incurred with handling
* those (now redundant) interrupts.
*/
static void rpmsg_downref_sleepers(struct virtproc_info *vrp)
{
/* support multiple concurrent senders */
mutex_lock(&vrp->tx_lock);
/* are we the last sleeping context waiting for tx buffers ? */
if (atomic_dec_and_test(&vrp->sleepers))
/* disable "tx-complete" interrupts */
virtqueue_disable_cb(vrp->svq);
mutex_unlock(&vrp->tx_lock);
}
/**
* rpmsg_send_offchannel_raw() - send a message across to the remote processor
* @rpdev: the rpmsg channel
@@ -582,9 +526,6 @@ static int rpmsg_send_offchannel_raw(struct rpmsg_device *rpdev,
/* no free buffer ? wait for one (but bail after 15 seconds) */
while (!msg) {
/* enable "tx-complete" interrupts, if not already enabled */
rpmsg_upref_sleepers(vrp);
/*
* sleep until a free buffer is available or 15 secs elapse.
* the timeout period is not configurable because there's
@@ -595,9 +536,6 @@ static int rpmsg_send_offchannel_raw(struct rpmsg_device *rpdev,
(msg = get_a_tx_buf(vrp)),
msecs_to_jiffies(15000));
/* disable "tx-complete" interrupts if we're the last sleeper */
rpmsg_downref_sleepers(vrp);
/* timeout ? */
if (!err) {
dev_err(dev, "timeout waiting for a tx buffer\n");
@@ -676,6 +614,34 @@ static int virtio_rpmsg_trysendto(struct rpmsg_endpoint *ept, void *data,
return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, false);
}
static __poll_t virtio_rpmsg_poll(struct rpmsg_endpoint *ept, struct file *filp,
poll_table *wait)
{
struct rpmsg_device *rpdev = ept->rpdev;
struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
struct virtproc_info *vrp = vch->vrp;
__poll_t mask = 0;
poll_wait(filp, &vrp->sendq, wait);
/* support multiple concurrent senders */
mutex_lock(&vrp->tx_lock);
/*
* check for a free buffer, either:
* - we haven't used all of the available transmit buffers (half of the
* allocated buffers are used for transmit, hence num_bufs / 2), or,
* - we ask the virtqueue if there's a buffer available
*/
if (vrp->last_sbuf < vrp->num_bufs / 2 ||
!virtqueue_enable_cb(vrp->svq))
mask |= EPOLLOUT;
mutex_unlock(&vrp->tx_lock);
return mask;
}
static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept)
{
struct rpmsg_device *rpdev = ept->rpdev;
@@ -922,9 +888,6 @@ static int rpmsg_probe(struct virtio_device *vdev)
WARN_ON(err); /* sanity check; this can't really happen */
}
/* suppress "tx-complete" interrupts */
virtqueue_disable_cb(vrp->svq);
vdev->priv = vrp;
rpdev_ctrl = rpmsg_virtio_add_ctrl_dev(vdev);