linux-kernel - RE: [PATCH v5] PCI: Xilinx NWL: Modifying irq chip for legacy interrupts

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Date:   Tue, 7 Mar 2017 05:48:03 +0000
From:   Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
To:     Marc Zyngier <marc.zyngier@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "paul.gortmaker@...driver.com" <paul.gortmaker@...driver.com>,
        "colin.king@...onical.com" <colin.king@...onical.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "Ravikiran Gummaluri" <rgummal@...inx.com>
Subject: RE: [PATCH v5] PCI: Xilinx NWL: Modifying irq chip for legacy
 interrupts

Hi Marc,

can you please look into my last comments ?

Regards,
Bharat
> Subject: RE: [PATCH v5] PCI: Xilinx NWL: Modifying irq chip for legacy interrupts
> 
> Waiting for Marc's Reply...
> 
> > > -----Original Message-----
> > > From: Marc Zyngier [mailto:marc.zyngier@....com]
> > > Sent: Thursday, February 09, 2017 9:33 PM
> > > To: Bharat Kumar Gogada <bharatku@...inx.com>; bhelgaas@...gle.com;
> > > robh@...nel.org; paul.gortmaker@...driver.com;
> > > colin.king@...onical.com; linux-pci@...r.kernel.org
> > > Cc: linux-arm-kernel@...ts.infradead.org;
> > > linux-kernel@...r.kernel.org; michal.simek@...inx.com;
> > > arnd@...db.de; Ravikiran Gummaluri <rgummal@...inx.com>
> > > Subject: Re: [PATCH v5] PCI: Xilinx NWL: Modifying irq chip for
> > > legacy
> > interrupts
> > >
> > > On 09/02/17 15:16, Bharat Kumar Gogada wrote:
> > > >>
> > > >> On 09/02/17 12:01, Bharat Kumar Gogada wrote:
> > > >>>> On 06/02/17 07:03, Bharat Kumar Gogada wrote:
> > > >>>>> +static struct irq_chip nwl_leg_irq_chip = {
> > > >>>>> +	.name = "nwl_pcie:legacy",
> > > >>>>> +	.irq_enable = nwl_unmask_leg_irq,
> > > >>>>> +	.irq_disable = nwl_mask_leg_irq,
> > > >>>>
> > > >>>> You don't need these two if they are implemented in terms of
> > > mask/unmask.
> > > >>>
> > > >>> These are being invoked by some drivers other than interrupt flow.
> > > >>> Ex: drivers/net/wireless/ath/ath9k/main.c
> > > >>> static int ath_reset_internal(struct ath_softc *sc, struct
> > > >>> ath9k_channel *hchan) {
> > > >>>          ....
> > > >>>          disable_irq(sc->irq);
> > > >>>          tasklet_disable(&sc->intr_tq);
> > > >>>         ...
> > > >>>         ...
> > > >>>         enable_irq(sc->irq);
> > > >>>         spin_unlock_bh(&sc->sc_pcu_lock); } For us
> > > >>> masking/unmasking is the way to enable/disable interrupts.
> > > >>
> > > >> And if you looked at the way disable_irq is implemented, you
> > > >> would have found out that it falls back to masking if there is no
> > > >> disable method, preserving the semantic you expect.
> > > >>
> > > > Yes I did see, but this fall back requires extra
> > > > "IRQ_DISABLE_UNLAZY" flag to
> > > be set to each virq.
> > >
> > > No it doesn't. If you do a disable_irq(), the interrupt is flagged
> > > as disabled, but nothing gets done. If an interrupt actually fires,
> > > then the interrupts gets
> > masked,
> > > and the handler is not called.
> > Yes agreed, this is where the problem comes for us. Here is the
> > scenario Ex:drivers/net/wireless/ath/ath9k/main.c
> > static int ath_reset_internal(struct ath_softc *sc, struct
> > ath9k_channel *hchan) {
> >   ....
> >    ath9k_hw_set_interrupts(ah);
> >    ath9k_hw_enable_interrupts(ah);
> >    ...
> >   enable_irq(sc->irq);
> >   ...
> > }
> > If you observe this they enable hardware interrupts first and then
> > call enable_irq, at this point of time virq is in disabled state. So,
> > if interrupt is raised in this period of time the handler is never
> > invoked and DEASEERT_INTx will not be seen. As I mentioned in my
> > subject the irq line between bridge and GIC goes low only after it
> > sees DEASSERT_INTx. But since DEASSERT_INTx is never seen line is
> > always high causing cpu stall.
> > So for this kind of EP's we need those two methods.
> >
> > Bharat