linux-kernel - Re: [PATCH v3 3/9] gpio: 104-dio-48e: Migrate to the regmap-irq API

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Date:   Mon, 28 Nov 2022 11:56:15 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     William Breathitt Gray <william.gray@...aro.org>
Cc:     Michael Walle <michael@...le.cc>, linus.walleij@...aro.org,
        brgl@...ev.pl, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, broonie@...nel.org
Subject: Re: [PATCH v3 3/9] gpio: 104-dio-48e: Migrate to the regmap-irq API

On Mon, Nov 28, 2022 at 11:51:10AM +0200, Andy Shevchenko wrote:
> On Sun, Nov 27, 2022 at 05:00:40PM -0500, William Breathitt Gray wrote:
> > On Sun, Nov 27, 2022 at 07:31:48PM +0100, Michael Walle wrote:
> > > Am 2022-11-22 11:29, schrieb William Breathitt Gray:

...

> > > gpiochip doesn't seem to be the correct place, gpiochip_add_irqchip()
> > > is a noop for gpio-regmap, right? So using gpiochip_irqchip_init_hw()
> > > seems wrong.
> > > 
> > > Maybe make gpio-regmap call it on its own? But really we just connect
> > > the regmap-irq to the gpiochip irqdomain.
> > 
> > I think you're right, it feels strange to handle IRQ initialization via
> > the GPIO framework. Maybe somewhere in regmap_irq might be more
> > appropriate?
> 
> The problem that that callback solves is possible interrupt storm, spurious
> interrupts, and Use Before Initialized.
> 
> If you can guarantee that in your case it never happens, add a comment
> and go on.
> 
> (It might be useful to tweak code a bit and try CONFIG_DEBUG_SHIRQ=y)
> 
> > > What is the purpose of the
> > > .init_hw callback? I've looked at other drivers which use regmap-irq
> > > and they all seem to just initialize the hardware in their _probe().
> > > 
> > > -michael
> > 
> > I'm not opposed to initializing the hardware in _probe(), although I can
> > see merit in pushing that operation instead closer to the framework
> > where the initialization is actually relevant.
> > 
> > Andy, maybe you can shed some light about .init_hw; I think you
> > introduced it to gpiolib in commit 9411e3aaa6342.
> 
> It seems that commit message doesn't fully  explain the situation behind
> that change. But it was observed in real life, see above.

FWIW, real life example:
e986f0e602f1 ("pinctrl: intel: fix unexpected interrupt")

-- 
With Best Regards,
Andy Shevchenko