linux-kernel - RE: [PATCH 3/3] irqchip: renesas-rzg2l: Fix irq storm with edge trigger detection for TINT

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Date:   Tue, 19 Sep 2023 17:06:54 +0000
From:   Biju Das <biju.das.jz@...renesas.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>,
        Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Biju Das <biju.das.au@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>
Subject: RE: [PATCH 3/3] irqchip: renesas-rzg2l: Fix irq storm with edge
 trigger detection for TINT

Hi Marc Zyngier,

> Subject: Re: [PATCH 3/3] irqchip: renesas-rzg2l: Fix irq storm with edge
> trigger detection for TINT
> 
> On Tue, 19 Sep 2023 17:32:05 +0100,
> Biju Das <biju.das.jz@...renesas.com> wrote:
> 
> [...]
> 
> > > So you mean that you *already* lose interrupts across a disable
> > > followed by an enable? I'm slightly puzzled...
> >
> > There is no interrupt lost at all.
> >
> > Currently this patch addresses 2 issues.
> >
> > Scenario 1: Extra interrupt when we select TINT source on enable_irq()
> >
> > Getting an extra interrupt, when client drivers calls enable_irq()
> > during probe()/resume(). In this case, the irq handler on the Client
> > driver just clear the interrupt status bit.
> >
> > Issue 2: IRQ storm when we select TINT source on enable_irq()
> >
> > Here as well, we are getting an extra interrupt, when client drivers
> > calls enable_irq() during probe() and this Interrupts getting
> > generated infinitely, when the client driver calls disable_irq() in
> > irq handler and in in work queue calling enable_irq().
> 
> How do you know this is a spurious interrupt? 

We have PMOD on RZ/G2L SMARC EVK. So I connected it to GPIO pin
and other end to ground. During the boot, I get an interrupt
even though there is no high to low transition, when the IRQ is setup
in the probe(). From this it is a spurious interrupt.

> For all you can tell, you are
> just consuming an edge. I absolutely don't buy this workaround, because you
> have no context that allows you to discriminate between a real spurious
> interrupt and a normal interrupt that lands while the interrupt line was
> masked.
> 
> > Currently we are not loosing interrupts, but we are getting additional
> > Interrupt(phantom) which is causing the issue.
> 
> If you get an interrupt at probe time in the endpoint driver, that's
> probably because the device is not in a quiescent state when the interrupt
> is requested. And it is probably this that needs addressing.

Any pointer for addressing this issue? 

Thanks for your help.

Cheers,
Biju