linux-kernel - Re: [PATCH 16/23] gpio: nomadik: support shared GPIO IRQs

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Message-Id: <CZ96EIJ22CYS.1AMRRY388V466@bootlin.com>
Date: Mon, 19 Feb 2024 16:54:55 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Bartosz Golaszewski" <brgl@...ev.pl>
Cc: "Linus Walleij" <linus.walleij@...aro.org>, "Rob Herring"
 <robh+dt@...nel.org>, "Krzysztof Kozlowski"
 <krzysztof.kozlowski+dt@...aro.org>, "Conor Dooley" <conor+dt@...nel.org>,
 "Philipp Zabel" <p.zabel@...gutronix.de>, "Thomas Bogendoerfer"
 <tsbogend@...ha.franken.de>, <linux-gpio@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-mips@...r.kernel.org>,
 "Gregory CLEMENT" <gregory.clement@...tlin.com>, "Vladimir Kondratiev"
 <vladimir.kondratiev@...ileye.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>, "Tawfik Bayouk"
 <tawfik.bayouk@...ileye.com>
Subject: Re: [PATCH 16/23] gpio: nomadik: support shared GPIO IRQs

Hello,

On Mon Feb 19, 2024 at 4:48 PM CET, Bartosz Golaszewski wrote:
> On Wed, Feb 14, 2024 at 5:24 PM Théo Lebrun <theo.lebrun@...tlin.com> wrote:
> >
> > Support a single IRQs used by multiple GPIO banks. Change the IRQ
> > handler type from a chained handler (as used by gpiolib
> > for ->parent_handler) to a threaded IRQ.
> >
> > Use a fake raw spinlock to ensure generic_handle_irq() is called in a
> > no-irq context. See Documentation/driver-api/gpio/driver.rst, "CHAINED
> > CASCADED GPIO IRQCHIPS" for additional information.
> >
>
> Any reason for not using preempt_disable()?

I did what the doc recommended:

> The generic_handle_irq() is expected to be called with IRQ disabled,
> so the IRQ core will complain if it is called from an IRQ handler which is
> forced to a thread. The "fake?" raw lock can be used to work around this
> problem::
>
>   raw_spinlock_t wa_lock;
>   static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank)
>       unsigned long wa_lock_flags;
>       raw_spin_lock_irqsave(&bank->wa_lock, wa_lock_flags);
>       generic_handle_irq(irq_find_mapping(bank->chip.irq.domain, bit));
>       raw_spin_unlock_irqrestore(&bank->wa_lock, wa_lock_flags);

If you confirm I should be using preempt_disable() that's what I'll do
in the next revision. I could even throw in a documentation patch if
the advice is outdated.

Thanks Bartosz,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com