dwc_otg: implement tasklet for returning URBs to usbcore hcd layer

The dwc_otg driver interrupt handler for transfer completion will spend
a very long time with interrupts disabled when a URB is completed -
this is because usb_hcd_giveback_urb is called from within the handler
which for a USB device driver with complicated processing (e.g. webcam)
will take an exorbitant amount of time to complete. This results in
missed completion interrupts for other USB packets which lead to them
being dropped due to microframe overruns.

This patch splits returning the URB to the usb hcd layer into a
high-priority tasklet. This will have most benefit for isochronous IN
transfers but will also have incidental benefit where multiple periodic
devices are active at once.

Author: P33M

drivers/usb/host/dwc_common_port/dwc_common_linux.c

@@ -991,6 +991,11 @@ void DWC_TASK_SCHEDULE(dwc_tasklet_t *task)
 	tasklet_schedule(&task->t);
 }
 
+void DWC_TASK_HI_SCHEDULE(dwc_tasklet_t *task)
+{
+	tasklet_hi_schedule(&task->t);
+}
+
 
 /* workqueues
  - run in process context (can sleep)

drivers/usb/host/dwc_common_port/dwc_list.h

@@ -384,17 +384,17 @@ struct {								\
 #define DWC_TAILQ_PREV(elm, headname, field)				\
 	(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 #define DWC_TAILQ_EMPTY(head)						\
-	(TAILQ_FIRST(head) == TAILQ_END(head))
+	(DWC_TAILQ_FIRST(head) == DWC_TAILQ_END(head))
 
 #define DWC_TAILQ_FOREACH(var, head, field)				\
-	for((var) = TAILQ_FIRST(head);					\
-	    (var) != TAILQ_END(head);					\
-	    (var) = TAILQ_NEXT(var, field))
+	for ((var) = DWC_TAILQ_FIRST(head);				\
+	    (var) != DWC_TAILQ_END(head);				\
+	    (var) = DWC_TAILQ_NEXT(var, field))
 
 #define DWC_TAILQ_FOREACH_REVERSE(var, head, headname, field)		\
-	for((var) = TAILQ_LAST(head, headname);				\
-	    (var) != TAILQ_END(head);					\
-	    (var) = TAILQ_PREV(var, headname, field))
+	for ((var) = DWC_TAILQ_LAST(head, headname);			\
+	    (var) != DWC_TAILQ_END(head);				\
+	    (var) = DWC_TAILQ_PREV(var, headname, field))
 
 /*
  * Tail queue functions.

drivers/usb/host/dwc_common_port/dwc_os.h

@@ -981,6 +981,8 @@ extern void DWC_TASK_FREE(dwc_tasklet_t *task);
 extern void DWC_TASK_SCHEDULE(dwc_tasklet_t *task);
 #define dwc_task_schedule DWC_TASK_SCHEDULE
 
+extern void DWC_TASK_HI_SCHEDULE(dwc_tasklet_t *task);
+#define dwc_task_hi_schedule DWC_TASK_HI_SCHEDULE
 
 /** @name Timer
  *

drivers/usb/host/dwc_otg/dwc_otg_hcd.c

@@ -40,6 +40,9 @@
  * header file.
  */
 
+#include <linux/usb.h>
+#include <linux/usb/hcd.h>
+
 #include "dwc_otg_hcd.h"
 #include "dwc_otg_regs.h"
 
@@ -694,6 +697,31 @@ static void reset_tasklet_func(void *data)
 	dwc_otg_hcd->flags.b.port_reset_change = 1;
 }
 
+static void completion_tasklet_func(void *ptr)
+{
+	dwc_otg_hcd_t *hcd = (dwc_otg_hcd_t *) ptr;
+	struct urb *urb;
+	urb_tq_entry_t *item;
+	dwc_irqflags_t flags;
+
+	DWC_SPINLOCK_IRQSAVE(hcd->lock, &flags);
+	while (!DWC_TAILQ_EMPTY(&hcd->completed_urb_list)) {
+		item = DWC_TAILQ_FIRST(&hcd->completed_urb_list);
+		urb = item->urb;
+		DWC_TAILQ_REMOVE(&hcd->completed_urb_list, item,
+				urb_tq_entries);
+		DWC_SPINUNLOCK_IRQRESTORE(hcd->lock, flags);
+		DWC_FREE(item);
+
+		usb_hcd_unlink_urb_from_ep(hcd->priv, urb);
+		usb_hcd_giveback_urb(hcd->priv, urb, urb->status);
+
+		DWC_SPINLOCK_IRQSAVE(hcd->lock, &flags);
+	}
+	DWC_SPINUNLOCK_IRQRESTORE(hcd->lock, flags);
+	return;
+}
+
 static void qh_list_free(dwc_otg_hcd_t * hcd, dwc_list_link_t * qh_list)
 {
 	dwc_list_link_t *item;
@@ -833,6 +861,7 @@ static void dwc_otg_hcd_free(dwc_otg_hcd_t * dwc_otg_hcd)
 
 	DWC_TIMER_FREE(dwc_otg_hcd->conn_timer);
 	DWC_TASK_FREE(dwc_otg_hcd->reset_tasklet);
+	DWC_TASK_FREE(dwc_otg_hcd->completion_tasklet);
 
 #ifdef DWC_DEV_SRPCAP
 	if (dwc_otg_hcd->core_if->power_down == 2 &&
@@ -877,7 +906,7 @@ int dwc_otg_hcd_init(dwc_otg_hcd_t * hcd, dwc_otg_core_if_t * core_if)
 	DWC_LIST_INIT(&hcd->periodic_sched_ready);
 	DWC_LIST_INIT(&hcd->periodic_sched_assigned);
 	DWC_LIST_INIT(&hcd->periodic_sched_queued);
-
+	DWC_TAILQ_INIT(&hcd->completed_urb_list);
 	/*
 	 * Create a host channel descriptor for each host channel implemented
 	 * in the controller. Initialize the channel descriptor array.
@@ -915,6 +944,9 @@ int dwc_otg_hcd_init(dwc_otg_hcd_t * hcd, dwc_otg_core_if_t * core_if)
 
 	/* Initialize reset tasklet. */
 	hcd->reset_tasklet = DWC_TASK_ALLOC("reset_tasklet", reset_tasklet_func, hcd);
+
+	hcd->completion_tasklet = DWC_TASK_ALLOC("completion_tasklet",
+						completion_tasklet_func, hcd);
 #ifdef DWC_DEV_SRPCAP
 	if (hcd->core_if->power_down == 2) {
 		/* Initialize Power on timer for Host power up in case hibernation */

drivers/usb/host/dwc_otg/dwc_otg_hcd.h

@@ -374,6 +374,13 @@ typedef struct dwc_otg_qh {
 
 DWC_CIRCLEQ_HEAD(hc_list, dwc_hc);
 
+typedef struct urb_tq_entry {
+	struct urb *urb;
+	DWC_TAILQ_ENTRY(urb_tq_entry) urb_tq_entries;
+} urb_tq_entry_t;
+
+DWC_TAILQ_HEAD(urb_list, urb_tq_entry);
+
 /**
  * This structure holds the state of the HCD, including the non-periodic and
  * periodic schedules.
@@ -551,6 +558,9 @@ struct dwc_otg_hcd {
 	/* Tasket to do a reset */
 	dwc_tasklet_t *reset_tasklet;
 
+	dwc_tasklet_t *completion_tasklet;
+	struct urb_list completed_urb_list;
+
 	/*  */
 	dwc_spinlock_t *lock;
 	dwc_spinlock_t *channel_lock;

drivers/usb/host/dwc_otg/dwc_otg_hcd_linux.c

@@ -271,7 +271,7 @@ static int _complete(dwc_otg_hcd_t * hcd, void *urb_handle,
 		     dwc_otg_hcd_urb_t * dwc_otg_urb, int32_t status)
 {
 	struct urb *urb = (struct urb *)urb_handle;
-
+	urb_tq_entry_t *new_entry;
 	if (CHK_DEBUG_LEVEL(DBG_HCDV | DBG_HCD_URB)) {
 		DWC_PRINTF("%s: urb %p, device %d, ep %d %s, status=%d\n",
 			   __func__, urb, usb_pipedevice(urb->pipe),
@@ -285,7 +285,7 @@ static int _complete(dwc_otg_hcd_t * hcd, void *urb_handle,
 			}
 		}
 	}
-
+	new_entry = DWC_ALLOC_ATOMIC(sizeof(urb_tq_entry_t));
 	urb->actual_length = dwc_otg_hcd_urb_get_actual_length(dwc_otg_urb);
 	/* Convert status value. */
 	switch (status) {
@@ -348,18 +348,25 @@ static int _complete(dwc_otg_hcd_t * hcd, void *urb_handle,
 	}
 
 	DWC_FREE(dwc_otg_urb);
-
+	if (!new_entry) {
+		DWC_ERROR("dwc_otg_hcd: complete: cannot allocate URB TQ entry\n");
+		urb->status = -EPROTO;
+		/* don't schedule the tasklet -
+		 * directly return the packet here with error. */
 #if USB_URB_EP_LINKING
-        usb_hcd_unlink_urb_from_ep(dwc_otg_hcd_to_hcd(hcd), urb);
+		usb_hcd_unlink_urb_from_ep(dwc_otg_hcd_to_hcd(hcd), urb);
 #endif
-	DWC_SPINUNLOCK(hcd->lock);
 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,28)
-	usb_hcd_giveback_urb(dwc_otg_hcd_to_hcd(hcd), urb);
+		usb_hcd_giveback_urb(dwc_otg_hcd_to_hcd(hcd), urb);
 #else
-	usb_hcd_giveback_urb(dwc_otg_hcd_to_hcd(hcd), urb, status);
+		usb_hcd_giveback_urb(dwc_otg_hcd_to_hcd(hcd), urb, urb->status);
 #endif
-	DWC_SPINLOCK(hcd->lock);
-
+	} else {
+		new_entry->urb = urb;
+		DWC_TAILQ_INSERT_TAIL(&hcd->completed_urb_list, new_entry,
+					urb_tq_entries);
+		DWC_TASK_HI_SCHEDULE(hcd->completion_tasklet);
+	}
 	return 0;
 }