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

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Date:   Fri, 22 Sep 2023 14:34:51 +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,

Thanks for the feedback.

> Subject: Re: [PATCH 3/3] irqchip: renesas-rzg2l: Fix irq storm with edge
> trigger detection for TINT
> 
> On Tue, 19 Sep 2023 18:06:54 +0100,
> Biju Das <biju.das.jz@...renesas.com> wrote:
> >
> > 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.
> 
> That doesn't really handle my question. At the point of enabling the
> interrupt and consuming the edge (which is what this patch does), how do
> you know you can readily discard this signal? This is a genuine question.
> 
> Spurious interrupts at boot are common. The HW resets in a funky,
> unspecified state, and it's SW's job to initialise it before letting other
> agents in the system use interrupts.

I got your point related to loosing interrupts.

Now I can detect spurious interrupts for edge trigger.

Pin controller driver has a read-only register to monitor input values of GPIO input pins, use that register values before/after rzg2l_irq_enable() with TINT Status Control Register (TSCR)
in IRQ controller to detect the spurious interrupt.

Eg:
1) Check PIN_43_0 value (ex: low)in pinctrl driver
2) Enable the IRQ using rzg2l_irq_enable()/ irq_chip_enable_parent()in pinctrl driver
3) Check PIN_43_0 value (ex: low) in pinctrl driver
4) Check the TINT Status Control Register(TSCR) in IRQ controller driver

     If the values in 1 and 3 are same and the status in 4 is set, then there 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?
> 
> Nothing but the most basic stuff: you should make sure that the interrupt
> isn't enabled before you can actually handle it, and triage it as spurious.

For the GPIO interrupt case I have,

RTC driver(endpoint)--> Pin controller driver -->IRQ controller driver-->GIC controller.

1) I have configured the pin as GPIO interrupts in pin controller driver
2) Set the IRQ detection in IRQ controller for edge trigger
3) The moment I set the IRQ source in IRQ controller 
   I get an interrupt, even though there is no voltage transition.

Here the system is setup properly, but there is a spurious interrupt. Currently don't know how to handle it? 

Any pointers for handling this issue?

Note:
 Currently the pin controller driver is not configuring GPIO as GPIO input in Port Mode Register for the GPIO interrupts instead it is using reset value which is "Hi-Z". I will send a patch to fix it.

Cheers,
Biju