linux-kernel - Re: [PATCH 1/1] pinctrl: ocelot: fix system hang on level based interrupts

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Message-ID: <CACRpkdZh_XZOKJa1Ga5vyh3MvY_yb7hDowbuJv-LG47AoZ+UCw@mail.gmail.com>
Date: Fri, 11 Oct 2024 22:02:44 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Sergey Matsievskiy <matsievskiysv@...il.com>
Cc: alexandre.belloni@...tlin.com, quentin.schulz@...tlin.com, 
	lars.povlsen@...rochip.com, horatiu.vultur@...rochip.com, 
	andriy.shevchenko@...ux.intel.com, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org, 
	UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH 1/1] pinctrl: ocelot: fix system hang on level based interrupts

On Fri, Oct 11, 2024 at 5:40 PM Sergey Matsievskiy
<matsievskiysv@...il.com> wrote:
> On Fri, Oct 11, 2024 at 11:18:55AM +0200, Linus Walleij wrote:

> > I'm a bit puzzled by the patch because I don't understand it.
>
> The current implementation only calls chained_irq_enter() and chained_irq_exit()
> if it detects pending interrupts.
>
> ```
> for (i = 0; i < info->stride; i++) {
>         uregmap_read(info->map, id_reg + 4 * i, &reg);
>         if (!reg)
>                 continue;
>
>         chained_irq_enter(parent_chip, desc);
> ```
>
> However, in case of GPIO pin configured in level mode and the parent controller
> configured in edge mode, GPIO interrupt might be lowered by the hardware. In the
> result,if the interrupt is short enough, the parent interrupt is still pending
> while the GPIO interrupt is cleared; chained_irq_enter() never gets called and
> the system hangs trying to service the parent interrupt.
>
> Moving chained_irq_enter() and chained_irq_exit() outside the for loop ensures
> that they are called even when GPIO interrupt is lowered by the hardware.
>
> The similar code with chained_irq_enter() / chained_irq_exit() functions
> wrapping interrupt checking loop may be found in many other drivers:
> ```
> grep -r -A 10 chained_irq_enter drivers/pinctrl
> ```
>
> > This needs to describe how moving the chained irq calls achieves
> > this effect.
>
> If the explanation above satisfies you, I'll elaborate the commit message and
> resend the patch.

Excellent explanation Sergey, just put it all in the committ message
and I'll apply it!

Yours,
Linus Walleij