On Wed, Oct 22, 2025 at 02:28:17PM +1100, [email protected] wrote:
> From: Patrick Oppenlander <[email protected]>
>
> 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 <[email protected]>
> ---
> drivers/rpmsg/virtio_rpmsg_bus.c | 101 ++++++++++---------------------
> 1 file changed, 32 insertions(+), 69 deletions(-)
>
As we previously agreed, I have added this patch to my tree under the condition
it doesn't break anything. Let's see how things go.
Thanks,
Mathieu
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c
> b/drivers/rpmsg/virtio_rpmsg_bus.c
> index 484890b4a6a74..79d983055b4d6 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);
> --
> 2.51.1.dirty
>
