staging: most: fix retrieval of buffer availability

This patch fixes the function channel_has_mbo that delivers the false
information in case two AIMs are using the same tx channel.
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

@@ -50,6 +50,11 @@ struct aim_channel {
 static struct list_head channel_list;
 static spinlock_t ch_list_lock;
 
+static inline bool ch_has_mbo(struct aim_channel *c)
+{
+	return channel_has_mbo(c->iface, c->channel_id, &cdev_aim) > 0;
+}
+
 static struct aim_channel *get_channel(struct most_interface *iface, int id)
 {
 	struct aim_channel *channel, *tmp;
@@ -279,11 +284,6 @@ aim_read(struct file *filp, char __user *buf, size_t count, loff_t *offset)
 	return copied;
 }
 
-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;
@@ -295,7 +295,7 @@ static unsigned int aim_poll(struct file *filp, poll_table *wait)
 		if (!kfifo_is_empty(&c->fifo))
 			mask |= POLLIN | POLLRDNORM;
 	} else {
-		if (!IS_ERR_OR_FALSE(channel_has_mbo(c->iface, c->channel_id)))
+		if (ch_has_mbo(c))
 			mask |= POLLOUT | POLLWRNORM;
 	}
 	return mask;

drivers/staging/most/mostcore/core.c

@@ -1352,7 +1352,7 @@ 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)
+int channel_has_mbo(struct most_interface *iface, int id, struct most_aim *aim)
 {
 	struct most_c_obj *c = get_channel_by_iface(iface, id);
 	unsigned long flags;
@@ -1361,6 +1361,11 @@ int channel_has_mbo(struct most_interface *iface, int id)
 	if (unlikely(!c))
 		return -EINVAL;
 
+	if (c->aim0.refs && c->aim1.refs &&
+	    ((aim == c->aim0.ptr && c->aim0.num_buffers <= 0) ||
+	     (aim == c->aim1.ptr && c->aim1.num_buffers <= 0)))
+		return 0;
+
 	spin_lock_irqsave(&c->fifo_lock, flags);
 	empty = list_empty(&c->fifo);
 	spin_unlock_irqrestore(&c->fifo_lock, flags);

drivers/staging/most/mostcore/mostcore.h

@@ -310,7 +310,8 @@ 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 channel_has_mbo(struct most_interface *iface, int channel_idx,
+		    struct most_aim *aim);
 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,