linux-kernel - Re: [PATCH v1] gpio: pca953x: fix IRQ storm on system wake up

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Message-ID: <02cab60d-9748-4227-a4aa-33373ea0be38@gmail.com>
Date: Mon, 7 Apr 2025 17:11:14 +0200
From: Emanuele Ghidoli <ghidoliemanuele@...il.com>
To: Bartosz Golaszewski <brgl@...ev.pl>,
 Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>,
 Linus Walleij <linus.walleij@...aro.org>,
 Francesco Dolcini <francesco@...cini.it>,
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
 Emanuele Ghidoli <emanuele.ghidoli@...adex.com>, linux-gpio@...r.kernel.org,
 linux-kernel@...r.kernel.org, Marek Vasut <marek.vasut@...il.com>,
 stable@...r.kernel.org, Francesco Dolcini <francesco.dolcini@...adex.com>
Subject: Re: [PATCH v1] gpio: pca953x: fix IRQ storm on system wake up

On 03/04/2025 15:56, Bartosz Golaszewski wrote:
> On Thu, Apr 3, 2025 at 3:54 PM Andy Shevchenko
> <andriy.shevchenko@...el.com> wrote:
>>
>> +Cc: Geert
>>
>> On Thu, Apr 03, 2025 at 02:07:05PM +0200, Bartosz Golaszewski wrote:
>>> On Wed, 26 Mar 2025 18:38:38 +0100, Francesco Dolcini wrote:
>>
>>>> If an input changes state during wake-up and is used as an interrupt
>>>> source, the IRQ handler reads the volatile input register to clear the
>>>> interrupt mask and deassert the IRQ line. However, the IRQ handler is
>>>> triggered before access to the register is granted, causing the read
>>>> operation to fail.
>>>>
>>>> As a result, the IRQ handler enters a loop, repeatedly printing the
>>>> "failed reading register" message, until `pca953x_resume` is eventually
>>>> called, which restores the driver context and enables access to
>>>> registers.
>>
>> [...]
>>
>>> Applied, thanks!
>>
>> Won't this regress as it happens the last time [1]?
>>
>> [1]: https://lore.kernel.org/linux-gpio/CAMuHMdVnKX23yi7ir1LVxfXAMeeWMFzM+cdgSSTNjpn1OnC2xw@mail.gmail.com/
>>
> 
> Ah, good catch. I'm wondering what the right fix here is but don't
> really have any ideas at the moment. Any hints are appreciated.
> 
> For now, I'm dropping it.
> 
> Bart

I’ve found another possible solution: disable the PCA953x IRQ in
pca953x_suspend() and re-enable it in pca953x_resume().
This would prevent the ISR from being triggered while the regmap is in
cache-only mode.
The wake-up capability is preserved, since an IRQ can still wake the system
even when disabled with disable_irq(), as long as it has wake enabled.

This should avoid introducing regressions and still handle Geert’s use case
properly.

Andy, Bart, Geert - what do you think?