usb: dwc3: Offload IRQ handling to softirq context

Move interrupt handling from threaded IRQ context to a tasklet.
This may help in reducing latencies associated with starvation
caused by high priority softirq over threaded USB IRQ.

Change-Id: I2f988be9c484a6ee59236d9dfd7f06f07414ee96
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>

2 files changed, 27 insertions, 6 deletions

diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index d81eb941108f..89d6c06a2073 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -804,6 +804,8 @@ struct dwc3_scratchpad_array {
  * @usb3_u1u2_disable: if true, disable U1U2 low power modes in Superspeed mode.
  * @in_lpm: indicates if controller is in low power mode (no clocks)
  * @tx_fifo_size: Available RAM size for TX fifo allocation
+ * @irq: irq number
+ * @bh: tasklet which handles the interrupt
  * @irq_cnt: total irq count
  * @bh_completion_time: time taken for taklet completion
  * @bh_handled_evt_cnt: no. of events handled by tasklet per interrupt
@@ -966,6 +968,8 @@ struct dwc3 {
 	int			tx_fifo_size;
 
 	/* IRQ timing statistics */
+	int			irq;
+	struct tasklet_struct	bh;
 	unsigned long		irq_cnt;
 	unsigned                bh_completion_time[MAX_INTR_STATS];
 	unsigned                bh_handled_evt_cnt[MAX_INTR_STATS];
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 2246a5b9444e..5a9ea5a3731f 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1792,8 +1792,8 @@ static int dwc3_gadget_start(struct usb_gadget *g,
 	u32			reg;
 
 	irq = platform_get_irq(to_platform_device(dwc->dev), 0);
-	ret = request_threaded_irq(irq, dwc3_interrupt, dwc3_thread_interrupt,
-			IRQF_SHARED, "dwc3", dwc);
+	dwc->irq = irq;
+	ret = request_irq(irq, dwc3_interrupt, IRQF_SHARED, "dwc3", dwc);
 	if (ret) {
 		dev_err(dwc->dev, "failed to request irq #%d --> %d\n",
 				irq, ret);
@@ -1911,9 +1911,12 @@ static int dwc3_gadget_stop(struct usb_gadget *g)
 	unsigned long		flags;
 	int			irq;
 
+	dwc3_gadget_disable_irq(dwc);
+
+	tasklet_kill(&dwc->bh);
+
 	spin_lock_irqsave(&dwc->lock, flags);
 
-	dwc3_gadget_disable_irq(dwc);
 	__dwc3_gadget_ep_disable(dwc->eps[0]);
 	__dwc3_gadget_ep_disable(dwc->eps[1]);
 
@@ -3032,6 +3035,15 @@ static irqreturn_t dwc3_process_event_buf(struct dwc3 *dwc, u32 buf)
 	return ret;
 }
 
+static void dwc3_interrupt_bh(unsigned long param)
+{
+	struct dwc3 *dwc = (struct dwc3 *) param;
+
+	pm_runtime_get(dwc->dev);
+	dwc3_thread_interrupt(dwc->irq, dwc);
+	enable_irq(dwc->irq);
+}
+
 static irqreturn_t dwc3_thread_interrupt(int irq, void *_dwc)
 {
 	struct dwc3 *dwc = _dwc;
@@ -3121,10 +3133,12 @@ static irqreturn_t dwc3_interrupt(int irq, void *_dwc)
 	dwc->irq_event_count[dwc->irq_dbg_index] = temp_cnt / 4;
 	dwc->irq_dbg_index = (dwc->irq_dbg_index + 1) % MAX_INTR_STATS;
 
-	if (ret == IRQ_WAKE_THREAD)
-		pm_runtime_get(dwc->dev);
+	if (ret == IRQ_WAKE_THREAD) {
+		disable_irq_nosync(irq);
+		tasklet_schedule(&dwc->bh);
+	}
 
-	return ret;
+	return IRQ_HANDLED;
 }
 
 /**
@@ -3170,6 +3184,9 @@ int dwc3_gadget_init(struct dwc3 *dwc)
 		goto err3;
 	}
 
+	dwc->bh.func = dwc3_interrupt_bh;
+	dwc->bh.data = (unsigned long)dwc;
+
 	dwc->gadget.ops			= &dwc3_gadget_ops;
 	dwc->gadget.speed		= USB_SPEED_UNKNOWN;
 	dwc->gadget.sg_supported	= true;