Index: uspace/lib/c/generic/device/hw_res.c
===================================================================
--- uspace/lib/c/generic/device/hw_res.c	(revision 9991c47fc8c46d0e24bc1c32ff3c50cc3e8b340d)
+++ uspace/lib/c/generic/device/hw_res.c	(revision 3df0f750d5542c7d884412d96aff44b1dca293ea)
@@ -42,14 +42,16 @@
 {
 	sysarg_t count = 0;
-	
+
 	async_exch_t *exch = async_exchange_begin(sess);
+	if (exch == NULL)
+		return ENOMEM;
 	int rc = async_req_1_1(exch, DEV_IFACE_ID(HW_RES_DEV_IFACE),
 	    HW_RES_GET_RESOURCE_LIST, &count);
-	
+
 	if (rc != EOK) {
 		async_exchange_end(exch);
 		return rc;
 	}
-	
+
 	size_t size = count * sizeof(hw_resource_t);
 	hw_resource_t *resources = (hw_resource_t *) malloc(size);
@@ -59,16 +61,16 @@
 		return ENOMEM;
 	}
-	
+
 	rc = async_data_read_start(exch, resources, size);
 	async_exchange_end(exch);
-	
+
 	if (rc != EOK) {
 		free(resources);
 		return rc;
 	}
-	
+
 	hw_resources->resources = resources;
 	hw_resources->count = count;
-	
+
 	return EOK;
 }
@@ -77,11 +79,26 @@
 {
 	async_exch_t *exch = async_exchange_begin(sess);
+	if (exch == NULL)
+		return false;
 	int rc = async_req_1_0(exch, DEV_IFACE_ID(HW_RES_DEV_IFACE),
 	    HW_RES_ENABLE_INTERRUPT);
 	async_exchange_end(exch);
-	
+
 	return (rc == EOK);
 }
 
+/**
+ * Setup DMA channel to specified place and mode.
+ * @param channel DMA Channel 1,2,3 for 8 bit transfers, 5,6,7 for 16 bit.
+ * @param pa Physical address of the buffer. Must be < 16MB for 16 bit and < 1MB
+ *           for 8 bit transfers.
+ * @param size DMA buffer size, limited to 64K.
+ * @param mode Mode of the DMA channel:
+ *              - Read or Write
+ *              - Allow automatic reset
+ *              - Use address decrement instead of increment
+ *              - Use SINGLE/BLOCK/ON DEMAND transfer mode
+ * @return Error code.
+ */
 int hw_res_dma_channel_setup(async_sess_t *sess,
     unsigned channel, uint32_t pa, uint16_t size, uint8_t mode)
@@ -90,9 +107,9 @@
 	if (exch == NULL)
 		return ENOMEM;
-	uint32_t packed = size | (mode << 16);
-	int ret = async_req_4_0(exch, DEV_IFACE_ID(HW_RES_DEV_IFACE),
+	const uint32_t packed = size | (mode << 16);
+	const int ret = async_req_4_0(exch, DEV_IFACE_ID(HW_RES_DEV_IFACE),
 	    HW_RES_DMA_CHANNEL_SETUP, channel, pa, packed);
 	async_exchange_end(exch);
-	
+
 	return ret;
 }