Index: uspace/drv/bus/usb/xhci/streams.c
===================================================================
--- uspace/drv/bus/usb/xhci/streams.c	(revision 5dab9ef0eac60d28c2266de9c442a55ca7f6b721)
+++ uspace/drv/bus/usb/xhci/streams.c	(revision 61e27e809067e0eca53b82b0a0af384b7c62a2e0)
@@ -39,4 +39,10 @@
 #include "streams.h"
 
+/** Finds stream data with given stream ID if it exists.
+ * Note that streams with ID 0, 65534 and 65535 are reserved.
+ * Splits the ID into primary and secondary context ID and searches the structures.
+ * @param[in] ep Affected endpoint.
+ * @param[in] stream_id Id of the stream.
+ */
 xhci_stream_data_t *xhci_get_stream_ctx_data(xhci_endpoint_t *ep, uint32_t stream_id)
 {
@@ -70,4 +76,8 @@
 }
 
+/** Initializes primary stream data structures in endpoint.
+ * @param[in] xhci_ep Used XHCI bulk endpoint.
+ * @param[in] count Amount of primary streams.
+ */
 static int initialize_primary_structures(xhci_endpoint_t *xhci_ep, unsigned count)
 {
@@ -91,4 +101,7 @@
 }
 
+/**
+ *
+ */
 static void clear_primary_structures(xhci_endpoint_t *xhci_ep)
 {
@@ -125,7 +138,7 @@
 }
 
-/** Initialize primary stream structure with given index.
- * @param[in] hc Host controller of the endpoint.
- * @param[in] xhci_epi XHCI bulk endpoint to use.
+/** Initialize a single primary stream structure with given index.
+ * @param[in] hc Host controller of the endpoint.
+ * @param[in] xhci_ep XHCI bulk endpoint to use.
  * @param[in] index index of the initialized stream structure.
  */
@@ -137,5 +150,5 @@
 	int err = EOK;
 
-	/* Init and register TRB ring for every primary stream */
+	/* Init and register TRB ring for the primary stream */
 	if ((err = xhci_trb_ring_init(&data->ring))) {
 		return err;
@@ -182,4 +195,5 @@
 {
 	if (count == 0) {
+		/* The primary stream context can still point to a single ring, not a secondary. */
 		return initialize_primary_stream(hc, xhci_ep, idx);
 	}
@@ -209,4 +223,5 @@
 	XHCI_STREAM_SCT_SET(*ctx, fnzb32(count) + 1);
 
+	/* Initialize all the rings. */
 	int err = EOK;
 	size_t index;
@@ -251,4 +266,10 @@
 }
 
+/** Verifies if all the common preconditions are satisfied.
+ * @param[in] hc Host controller of the endpoint.
+ * @param[in] dev Used device.
+ * @param[in] xhci_ep Associated XHCI bulk endpoint.
+ * @param[in] count Amount of primary streams requested.
+ */
 static int verify_stream_conditions(xhci_hc_t *hc, xhci_device_t *dev,
 	xhci_endpoint_t *xhci_ep, unsigned count)
@@ -270,5 +291,6 @@
 	}
 
-	uint8_t max_psa_size = 2 << XHCI_REG_RD(hc->cap_regs, XHCI_CAP_MAX_PSA_SIZE);
+	/* The maximum amount of primary streams is 2 ^ (MaxPSA + 1) (See table 26 of XHCI specification) */
+	uint8_t max_psa_size = 1 << (XHCI_REG_RD(hc->cap_regs, XHCI_CAP_MAX_PSA_SIZE) + 1);
 	if (count > max_psa_size) {
 		usb_log_error("Host controller only supports %u primary streams.", max_psa_size);
@@ -290,5 +312,9 @@
 }
 
-/** Initialize primary streams
+/** Initialize, setup and register primary streams.
+ * @param[in] hc Host controller of the endpoint.
+ * @param[in] dev Used device.
+ * @param[in] xhci_ep Associated XHCI bulk endpoint.
+ * @param[in] count Amount of primary streams requested.
  */
 int xhci_endpoint_request_primary_streams(xhci_hc_t *hc, xhci_device_t *dev,
@@ -313,4 +339,5 @@
 
 	xhci_ep_ctx_t ep_ctx;
+	/* Allowed values are 1-15, where 2 ^ pstreams is the actual amount of streams. */
 	const size_t pstreams = fnzb32(count) - 1;
 	setup_stream_context(xhci_ep, &ep_ctx, pstreams, 1);
@@ -320,7 +347,12 @@
 }
 
-/** Initialize secondary streams
- * sizes - the size of each secondary stream context (an array)
- * count - the amount of primary stream contexts
+/** Initialize, setup and register secondary streams.
+ * @param[in] hc Host controller of the endpoint.
+ * @param[in] dev Used device.
+ * @param[in] xhci_ep Associated XHCI bulk endpoint.
+ * @param[in] sizes Amount of secondary streams in each primary stream.
+ 					This array should have exactly count elements.
+					If the size is 0, then a primary ring is created with that index.
+ * @param[in] count Amount of primary streams requested.
  */
 int xhci_endpoint_request_secondary_streams(xhci_hc_t *hc, xhci_device_t *dev,