--- a/drivers/media/dvb/dvb-core/dvb_ca_en50221.c	2008-07-13 23:51:29.000000000 +0200
+++ b/drivers/media/dvb/dvb-core/dvb_ca_en50221.c	2008-08-22 09:05:31.000000000 +0200
@@ -93,6 +93,9 @@ struct dvb_ca_slot {
 	/* current state of the CAM */
 	int slot_state;
 
+	/* slot mutex for serializing data read/write access */
+	struct mutex slotlock;
+
 	/* Number of CAMCHANGES that have occurred since last processing */
 	atomic_t camchange_count;
 
@@ -589,6 +592,8 @@ static int dvb_ca_en50221_read_data(stru
 
 	dprintk("%s\n", __func__);
 
+	mutex_lock(&ca->slot_info[slot].slotlock);
+
 	/* check if we have space for a link buf in the rx_buffer */
 	if (ebuf == NULL) {
 		int buf_free;
@@ -687,6 +692,7 @@ static int dvb_ca_en50221_read_data(stru
 	status = bytes_read;
 
 exit:
+	mutex_unlock(&ca->slot_info[slot].slotlock);
 	return status;
 }
 
@@ -710,15 +716,22 @@ static int dvb_ca_en50221_write_data(str
 
 	dprintk("%s\n", __func__);
 
+	mutex_lock(&ca->slot_info[slot].slotlock);
 
-	// sanity check
+	/* sanity check */
 	if (bytes_write > ca->slot_info[slot].link_buf_size)
 		return -EINVAL;
 
-	/* check if interface is actually waiting for us to read from it, or if a read is in progress */
+	/* it is possible we are dealing with a single buffer implementation,
+	   thus if there is data available for read or if there is even a read
+	   already in progress, we do nothing but awake the kernel thread to
+	   process the data if necessary. */
 	if ((status = ca->pub->read_cam_control(ca->pub, slot, CTRLIF_STATUS)) < 0)
 		goto exitnowrite;
 	if (status & (STATUSREG_DA | STATUSREG_RE)) {
+		if (status & STATUSREG_DA)
+			dvb_ca_en50221_thread_wakeup(ca);
+
 		status = -EAGAIN;
 		goto exitnowrite;
 	}
@@ -767,6 +780,7 @@ exit:
 	ca->pub->write_cam_control(ca->pub, slot, CTRLIF_COMMAND, IRQEN);
 
 exitnowrite:
+	mutex_unlock(&ca->slot_info[slot].slotlock);
 	return status;
 }
 EXPORT_SYMBOL(dvb_ca_en50221_camchange_irq);
@@ -1662,6 +1676,7 @@ int dvb_ca_en50221_init(struct dvb_adapt
 	for (i = 0; i < slot_count; i++) {
 		memset(&ca->slot_info[i], 0, sizeof(struct dvb_ca_slot));
 		ca->slot_info[i].slot_state = DVB_CA_SLOTSTATE_NONE;
+		mutex_init(&ca->slot_info[i].slotlock);
 		atomic_set(&ca->slot_info[i].camchange_count, 0);
 		ca->slot_info[i].camchange_type = DVB_CA_EN50221_CAMCHANGE_REMOVED;
 	}