staging: most: add poll syscall to AIM cdev

This patch adds the implementation of the poll syscall to the AIM cdev.
To have the full functionality, a helper function is needed in the
core module to retrieve the instantaneous availability of tx buffers.
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/most/aim-cdev/cdev.c

@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/device.h>
 #include <linux/cdev.h>
+#include <linux/poll.h>
 #include <linux/kfifo.h>
 #include <linux/uaccess.h>
 #include <linux/idr.h>
@@ -31,6 +32,7 @@ static struct most_aim cdev_aim;
 
 struct aim_channel {
 	wait_queue_head_t wq;
+	wait_queue_head_t poll_wq;
 	struct cdev cdev;
 	struct device *dev;
 	struct mutex io_mutex;
@@ -271,6 +273,28 @@ aim_read(struct file *filp, char __user *buf, size_t count, loff_t *offset)
 	return retval;
 }
 
+static inline bool __must_check IS_ERR_OR_FALSE(int x)
+{
+	return x <= 0;
+}
+
+static unsigned int aim_poll(struct file *filp, poll_table *wait)
+{
+	struct aim_channel *c = filp->private_data;
+	unsigned int mask = 0;
+
+	poll_wait(filp, &c->poll_wq, wait);
+
+	if (c->cfg->direction == MOST_CH_RX) {
+		if (!kfifo_is_empty(&c->fifo))
+			mask |= POLLIN | POLLRDNORM;
+	} else {
+		if (!IS_ERR_OR_FALSE(channel_has_mbo(c->iface, c->channel_id)))
+			mask |= POLLOUT | POLLWRNORM;
+	}
+	return mask;
+}
+
 /**
  * Initialization of struct file_operations
  */
@@ -280,6 +304,7 @@ static const struct file_operations channel_fops = {
 	.write = aim_write,
 	.open = aim_open,
 	.release = aim_close,
+	.poll = aim_poll,
 };
 
 /**
@@ -434,6 +459,7 @@ static int aim_probe(struct most_interface *iface, int channel_id,
 		goto error_alloc_kfifo;
 	}
 	init_waitqueue_head(&channel->wq);
+	init_waitqueue_head(&channel->poll_wq);
 	mutex_init(&channel->io_mutex);
 	spin_lock_irqsave(&ch_list_lock, cl_flags);
 	list_add_tail(&channel->list, &channel_list);

drivers/staging/most/mostcore/core.c

@@ -1383,6 +1383,22 @@ most_c_obj *get_channel_by_iface(struct most_interface *iface, int id)
 	return i->channel[id];
 }
 
+int channel_has_mbo(struct most_interface *iface, int id)
+{
+	struct most_c_obj *c = get_channel_by_iface(iface, id);
+	unsigned long flags;
+	int empty;
+
+	if (unlikely(!c))
+		return -EINVAL;
+
+	spin_lock_irqsave(&c->fifo_lock, flags);
+	empty = list_empty(&c->fifo);
+	spin_unlock_irqrestore(&c->fifo_lock, flags);
+	return !empty;
+}
+EXPORT_SYMBOL_GPL(channel_has_mbo);
+
 /**
  * most_get_mbo - get pointer to an MBO of pool
  * @iface: pointer to interface instance

drivers/staging/most/mostcore/mostcore.h

@@ -311,6 +311,7 @@ int most_deregister_aim(struct most_aim *aim);
 struct mbo *most_get_mbo(struct most_interface *iface, int channel_idx,
 			 struct most_aim *);
 void most_put_mbo(struct mbo *mbo);
+int channel_has_mbo(struct most_interface *iface, int channel_idx);
 int most_start_channel(struct most_interface *iface, int channel_idx,
 		       struct most_aim *);
 int most_stop_channel(struct most_interface *iface, int channel_idx,