rpmsg: virtio: EPOLLOUT support

 * @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

	struct idr endpoints;

	struct mutex endpoints_lock;

	wait_queue_head_t sendq;

	atomic_t sleepers;

};

/* The feature bitmap for virtio rpmsg */

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);

	.sendto = virtio_rpmsg_sendto,

	.trysend = virtio_rpmsg_trysend,

	.trysendto = virtio_rpmsg_trysendto,

	.poll = virtio_rpmsg_poll,

	.get_mtu = virtio_rpmsg_get_mtu,

};

	unsigned int len;

	void *ret;

	/* support multiple concurrent senders */

	mutex_lock(&vrp->tx_lock);

	/*

	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

	/* 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

					(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");

	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;

		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);