diff --git a/drivers/mfd/pcf50633-adc.c b/drivers/mfd/pcf50633-adc.c
index c2d05be..3d31e97 100644
--- a/drivers/mfd/pcf50633-adc.c
+++ b/drivers/mfd/pcf50633-adc.c
@@ -73,15 +73,10 @@
 	struct pcf50633_adc *adc = __to_adc(pcf);
 	int head;
 
-	mutex_lock(&adc->queue_mutex);
-
 	head = adc->queue_head;
 
-	if (!adc->queue[head]) {
-		mutex_unlock(&adc->queue_mutex);
+	if (!adc->queue[head])
 		return;
-	}
-	mutex_unlock(&adc->queue_mutex);
 
 	adc_setup(pcf, adc->queue[head]->mux, adc->queue[head]->avg);
 }
@@ -99,16 +94,17 @@
 
 	if (adc->queue[tail]) {
 		mutex_unlock(&adc->queue_mutex);
+		dev_err(pcf->dev, "ADC queue is full, dropping request\n");
 		return -EBUSY;
 	}
 
 	adc->queue[tail] = req;
+	if (head == tail)
+		trigger_next_adc_job_if_any(pcf);
 	adc->queue_tail = (tail + 1) & (PCF50633_MAX_ADC_FIFO_DEPTH - 1);
 
 	mutex_unlock(&adc->queue_mutex);
 
-	trigger_next_adc_job_if_any(pcf);
-
 	return 0;
 }
 
@@ -124,6 +120,7 @@
 int pcf50633_adc_sync_read(struct pcf50633 *pcf, int mux, int avg)
 {
 	struct pcf50633_adc_request *req;
+	int err;
 
 	/* req is freed when the result is ready, in interrupt handler */
 	req = kzalloc(sizeof(*req), GFP_KERNEL);
@@ -136,9 +133,13 @@
 	req->callback_param = req;
 
 	init_completion(&req->completion);
-	adc_enqueue_request(pcf, req);
+	err = adc_enqueue_request(pcf, req);
+	if (err)
+		return err;
+
 	wait_for_completion(&req->completion);
 
+	/* FIXME by this time req might be already freed */
 	return req->result;
 }
 EXPORT_SYMBOL_GPL(pcf50633_adc_sync_read);
@@ -159,9 +160,7 @@
 	req->callback = callback;
 	req->callback_param = callback_param;
 
-	adc_enqueue_request(pcf, req);
-
-	return 0;
+	return adc_enqueue_request(pcf, req);
 }
 EXPORT_SYMBOL_GPL(pcf50633_adc_async_read);
 
@@ -184,7 +183,7 @@
 	struct pcf50633_adc *adc = data;
 	struct pcf50633 *pcf = adc->pcf;
 	struct pcf50633_adc_request *req;
-	int head;
+	int head, res;
 
 	mutex_lock(&adc->queue_mutex);
 	head = adc->queue_head;
@@ -199,12 +198,13 @@
 	adc->queue_head = (head + 1) &
 				      (PCF50633_MAX_ADC_FIFO_DEPTH - 1);
 
+	res = adc_result(pcf);
+	trigger_next_adc_job_if_any(pcf);
+
 	mutex_unlock(&adc->queue_mutex);
 
-	req->callback(pcf, req->callback_param, adc_result(pcf));
+	req->callback(pcf, req->callback_param, res);
 	kfree(req);
-
-	trigger_next_adc_job_if_any(pcf);
 }
 
 static int __devinit pcf50633_adc_probe(struct platform_device *pdev)