linux-kernel - RE: CPU stall with TP-Link wifi PCIe card

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Date:   Thu, 1 Dec 2016 00:48:19 +0000
From:   Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
CC:     Bjorn Helgaas <helgaas@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        "arnd@...db.de" <arnd@...db.de>,
        "qnguyen@....com" <qnguyen@....com>,
        "jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "sudeep.holla@....com" <sudeep.holla@....com>
Subject: RE: CPU stall with TP-Link wifi PCIe card

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
> >