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 raspberrypi#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);