From c38d8b66c82c585199e2ad67282295f21cfa489f Mon Sep 17 00:00:00 2001 From: Patrick Oppenlander Date: Wed, 22 Oct 2025 14:28:17 +1100 Subject: [PATCH] rpmsg: virtio: EPOLLOUT support 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 Link: https://lore.kernel.org/r/20251022032817.320378-1-patrick.oppenlander@gmail.com Signed-off-by: Mathieu Poirier --- drivers/rpmsg/virtio_rpmsg_bus.c | 101 ++++++++++--------------------- 1 file changed, 32 insertions(+), 69 deletions(-) diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c index 484890b4a6a7..79d983055b4d 100644 --- a/drivers/rpmsg/virtio_rpmsg_bus.c +++ b/drivers/rpmsg/virtio_rpmsg_bus.c @@ -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); -- 2.47.3