dwc_otg: fix locking around dequeueing and killing URBs

kill_urbs_in_qh_list() is practically only ever called with the fiq lock
already held, so don't spinlock twice in the case where we need to cancel
an isochronous transfer.

Also fix up a case where the global interrupt register could be read with
the fiq lock not held.

Fixes the deadlock seen in #2907

drivers/usb/host/dwc_otg/dwc_otg_cil_intr.c

@@ -1344,16 +1344,21 @@ static inline uint32_t dwc_otg_read_common_intr(dwc_otg_core_if_t * core_if, gin
 		 */
 		gintmsk_common.b.portintr = 1;
 	}
-	gintsts.d32 = DWC_READ_REG32(&core_if->core_global_regs->gintsts);
-	gintmsk.d32 = DWC_READ_REG32(&core_if->core_global_regs->gintmsk);
 	if(fiq_enable) {
 		local_fiq_disable();
+		fiq_fsm_spin_lock(&hcd->fiq_state->lock);
+		gintsts.d32 = DWC_READ_REG32(&core_if->core_global_regs->gintsts);
+		gintmsk.d32 = DWC_READ_REG32(&core_if->core_global_regs->gintmsk);
 		/* Pull in the interrupts that the FIQ has masked */
 		gintmsk.d32 |= ~(hcd->fiq_state->gintmsk_saved.d32);
 		gintmsk.d32 |= gintmsk_common.d32;
 		/* for the upstairs function to reenable - have to read it here in case FIQ triggers again */
 		reenable_gintmsk->d32 = gintmsk.d32;
+		fiq_fsm_spin_unlock(&hcd->fiq_state->lock);
 		local_fiq_enable();
+	} else {
+		gintsts.d32 = DWC_READ_REG32(&core_if->core_global_regs->gintsts);
+		gintmsk.d32 = DWC_READ_REG32(&core_if->core_global_regs->gintmsk);
 	}
 
 	gahbcfg.d32 = DWC_READ_REG32(&core_if->core_global_regs->gahbcfg);

drivers/usb/host/dwc_otg/dwc_otg_hcd.c

@@ -195,15 +195,11 @@ static void kill_urbs_in_qh_list(dwc_otg_hcd_t * hcd, dwc_list_link_t * qh_list)
 			 * but not yet been through the IRQ handler.
 			 */
 			if (fiq_fsm_enable && (hcd->fiq_state->channel[qh->channel->hc_num].fsm != FIQ_PASSTHROUGH)) {
-				local_fiq_disable();
-				fiq_fsm_spin_lock(&hcd->fiq_state->lock);
 				qh->channel->halt_status = DWC_OTG_HC_XFER_URB_DEQUEUE;
 				qh->channel->halt_pending = 1;
 				if (hcd->fiq_state->channel[n].fsm == FIQ_HS_ISOC_TURBO ||
 					hcd->fiq_state->channel[n].fsm == FIQ_HS_ISOC_SLEEPING)
 					hcd->fiq_state->channel[n].fsm = FIQ_HS_ISOC_ABORTED;
-				fiq_fsm_spin_unlock(&hcd->fiq_state->lock);
-				local_fiq_enable();
 			} else {
 				dwc_otg_hc_halt(hcd->core_if, qh->channel,
 						DWC_OTG_HC_XFER_URB_DEQUEUE);