Re: [PATCH] usb: dwc3: Clear DWC3_EVENT_PENDING when count is 0

[Linyu Yuan]

On 2/3/2023 4:06 AM, Thinh Nguyen wrote:
> On Thu, Feb 02, 2023, Linyu Yuan wrote:
> > On 2/2/2023 2:57 AM, Thinh Nguyen wrote:
> > > On Tue, Jan 31, 2023, Linyu Yuan wrote:
> > > > hi Thinh,
> > > >
> > > >
> > > > regarding your suggestion, assume it is not PCIe type,  still have one
> > > > question,
> > > >
> > > >
> > > > -       if (evt->flags & DWC3_EVENT_PENDING)
> > > > +       if (evt->flags & DWC3_EVENT_PENDING) {
> > > > +               if (!evt->count) {
> > > > +                       u32 reg = dwc3_readl(dwc->regs, DWC3_GEVNTSIZ(0));
> > > > +
> > > > +                       if (!(reg & DWC3_GEVNTSIZ_INTMASK))
> > > > +                               evt->flags &= ~DWC3_EVENT_PENDING;
> > > >
> > > > do we need to return IRQ_WAKE_THREAD  ?
> > > No, if evt->count is 0, but GEVNTCOUNT is > 0, the controller will
> > > generate interrupt. The evt->count will be updated and the events will
> > > be handled on the next interrupt.
> >
> > when will next interrupt happen ?
> Immediately after. You can test this by just return IRQ_HANDLED and not
> clear the GEVNTCOUNT to see its behavior.


if it immediately, it will be good.


정재훈  could you update a new patch which Thinh suggest.

maybe we didn't find the root cause of irq strom, but the change have no side effect.


> > as when enter here, i guess GEVENTCOUNT is already > 0, but we didn't read
> > it.
> GEVNTCOUNT is always updating as new events are generated. We only clear
> however many events we process, but that doesn't stop it from
> incrementing.


just consider if there is a case that next GEVNETCOUNT increase which 
happen long time later,

maybe think too much.


> BR,
> Thinh
>
> > > > +               }
> > > >                   return IRQ_HANDLED;
> > > >
> > > > as here return IRQ HANDLED, how can we make sure a new IRQ will be handled
> > > > after previous IRQ thread clean PENDING flag ?
> > > If evt->count > 0, that means the bottom half is still running. So,
> > > leave it be. If evt->count == 0, then the cached events are processed,
> > > we're safe to clear the PENDING flag. New interrupt will be generated if
> > > GEVNTCOUNT is > 0.
> > >
> > > > +       }
> > > >
> > > >
> > > > also for non-PCIe controller, consider IRQ mask register working correctly,
> > > >
> > > > consider a case IRQ happen before IRQ thread exit,  here just return
> > > > IRQ_HANDLED.
> > > >
> > > > once IRQ thread exit, it will clean PENDING flag, so next IRQ event will run
> > > > normally.
> > > >
> > > > if 정재훈 saw PENDING flag is not cleared, does it mean IRQ thread have no
> > > > chance to exit ?
> > > The PENDING flag should be cleared eventually when the bottom half
> > > completes. I don't expect the interrupt storm to block the IRQ thread
> > > forever, but I can't guarantee the device behavor. 정재훈 can confirm.
> > > This change should resolve the interrupt storm.
> > >
> > > BR,
> > > Thinh