RE: CPU stall with TP-Link wifi PCIe card

RE: CPU stall with TP-Link wifi PCIe card

[Bharat Kumar Gogada]

After further debugging found that irq_enable is not being invoked by kernel in kernel/irq/chip.c after the few interrupts when we do wlan scan.

In ARM64, when an interrupt arises who invokes irq_disable(struct irq_desc *desc)/irq_enable(struct irq_desc *desc)
functions. 

>From my debugging for successful interrupt handling irq_disable->handler->irq_enabling is happening,
irrespective of IRQD_IRQ_DISABLED state, is it correct ?

Regards,
Bharat

> 
> Just to add, im using 4.6 kernel version. And the card is working on ARM, X86
> machine.
> 
> > Subject: CPU stall with TP-Link wifi PCIe card
> >
> > Hi,
> >
> > We are testing TP-link wifi PCIe card(TL-WDN4800) on our soc
> > (pcie-xilinx- nwl.c). This card is using legacy interrupts and it
> > doesn't support MSI.
> >
> > When we do scan on wifi interface(using "iw dev wlan0 scan") cpu is
> > getting stalled making whole system hang.
> >
> > After debugging found that IRQ is being disabled after getting 1 or 2
> > interrupts immediately after we run the scan command.
> >
> > But interrupts are being received to root port continuously but not
> > being serviced by EP due to following condition, due to continuous
> > interrupts cpu is getting stalled.
> >
> > In handle_simple_irq:
> >
> > if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
> >                 desc->istate |= IRQS_PENDING;
> >                 goto out_unlock;
> >   }
> >
> > The irqd_irq_disabled(&desc->irq_data) is returning 1 after 1 or 2
> > interrupts after we scan.
> >
> > Can any one tell why irq is going into disabled state ?
> >
> > What might be the source that's making it go into disabled state ?
> >
> > Thanks & Regards,
> > Bharat
> >

RE: CPU stall with TP-Link wifi PCIe card

[Thomas Gleixner]

On Thu, 1 Dec 2016, Bharat Kumar Gogada wrote:

> After further debugging found that irq_enable is not being invoked by
> kernel in kernel/irq/chip.c after the few interrupts when we do wlan
> scan.
>
> In ARM64, when an interrupt arises who invokes irq_disable(struct
> irq_desc *desc)/irq_enable(struct irq_desc *desc) functions.

What invokes irq_disable()/irq_enable()? In which function is this
happening? There are exactly three places in the interrupt core which
invoke irq_disable():

__disable_irq(), which is invoked from disable_irq() and
		 disable_irq_nosync() and suspend_device_irq()
       
irq_pm_check_wakeup(), whis suspend/wakeup related

note_interrupt(), which disables interrupt when the handler refuses to
		  handle them.

There is nothing in the core code which invokes irq_disable/enable() pairs
in any interrupt handling code path and I have no idea how ARM64 would do
that.

> From my debugging for successful interrupt handling
> irq_disable->handler->irq_enabling is happening, irrespective of
> IRQD_IRQ_DISABLED state, is it correct ?

To be honest, I have not the faintest clue what you are trying to
explain/ask.

> > Just to add, im using 4.6 kernel version. And the card is working on ARM, X86
> > machine.
> > 
> > > Subject: CPU stall with TP-Link wifi PCIe card
> > >
> > > Hi,
> > >
> > > We are testing TP-link wifi PCIe card(TL-WDN4800) on our soc
> > > (pcie-xilinx- nwl.c). This card is using legacy interrupts and it
> > > doesn't support MSI.

That card information is useless. Which driver is handling the card?

You are neither telling which interrupt controller is used for this legacy
interrupt.

> > > When we do scan on wifi interface(using "iw dev wlan0 scan") cpu is
> > > getting stalled making whole system hang.
> > >
> > > After debugging found that IRQ is being disabled after getting 1 or 2
> > > interrupts immediately after we run the scan command.
> > >
> > > But interrupts are being received to root port continuously but not
> > > being serviced by EP due to following condition, due to continuous
> > > interrupts cpu is getting stalled.
> > >
> > > In handle_simple_irq:
> > >
> > > if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
> > >                 desc->istate |= IRQS_PENDING;
> > >                 goto out_unlock;
> > >   }
> > >
> > > The irqd_irq_disabled(&desc->irq_data) is returning 1 after 1 or 2
> > > interrupts after we scan.

So the interrupt is disabled, but it's not masked in hardware.

> > > Can any one tell why irq is going into disabled state ?
> > >
> > > What might be the source that's making it go into disabled state ?

Simply a call to disable_irq() or disable_irq_nosync().

If you can come up with some coherent information about the problem instead
of weird theories and useless conclusions then we might be able to help.

Thanks,

	tglx

RE: CPU stall with TP-Link wifi PCIe card

[Bharat Kumar Gogada]

Just to add, im using 4.6 kernel version. And the card is working on ARM, X86 machine.

> Subject: CPU stall with TP-Link wifi PCIe card
> 
> Hi,
> 
> We are testing TP-link wifi PCIe card(TL-WDN4800) on our soc (pcie-xilinx-
> nwl.c). This card is using
> legacy interrupts and it doesn't support MSI.
> 
> When we do scan on wifi interface(using "iw dev wlan0 scan") cpu is getting
> stalled
> making whole system hang.
> 
> After debugging found that IRQ is being disabled after getting 1 or 2 interrupts
> immediately after we run the scan command.
> 
> But interrupts are being received to root port continuously but not being
> serviced by EP due to following
> condition, due to continuous interrupts cpu is getting stalled.
> 
> In handle_simple_irq:
> 
> if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
>                 desc->istate |= IRQS_PENDING;
>                 goto out_unlock;
>   }
> 
> The irqd_irq_disabled(&desc->irq_data) is returning 1 after 1 or 2 interrupts after
> we scan.
> 
> Can any one tell why irq is going into disabled state ?
> 
> What might be the source that's making it go into disabled state ?
> 
> Thanks & Regards,
> Bharat
> 

CPU stall with TP-Link wifi PCIe card

[Bharat Kumar Gogada]

Hi, 

We are testing TP-link wifi PCIe card(TL-WDN4800) on our soc (pcie-xilinx-nwl.c). This card is using 
legacy interrupts and it doesn't support MSI.

When we do scan on wifi interface(using "iw dev wlan0 scan") cpu is getting stalled 
making whole system hang.

After debugging found that IRQ is being disabled after getting 1 or 2 interrupts 
immediately after we run the scan command.

But interrupts are being received to root port continuously but not being serviced by EP due to following 
condition, due to continuous interrupts cpu is getting stalled. 

In handle_simple_irq:

if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
                desc->istate |= IRQS_PENDING;
                goto out_unlock;
  }    

The irqd_irq_disabled(&desc->irq_data) is returning 1 after 1 or 2 interrupts after we scan.

Can any one tell why irq is going into disabled state ?

What might be the source that's making it go into disabled state ?

Thanks & Regards,
Bharat