linux-kernel - Re: [PATCH v3 06/16] irqchip: add sl28cpld interrupt controller support

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Message-ID: <87sggopxe2.fsf@nanos.tec.linutronix.de>
Date:   Mon, 27 Apr 2020 21:00:05 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Michael Walle <michael@...le.cc>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Lee Jones <lee.jones@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v3 06/16] irqchip: add sl28cpld interrupt controller support

Michael,

Michael Walle <michael@...le.cc> writes:
> Am 2020-04-27 13:40, schrieb Thomas Gleixner:
>>> +
>>> +	ret = devm_regmap_add_irq_chip(&pdev->dev, irqchip->regmap, irq,
>>> +				       IRQF_SHARED | IRQF_ONESHOT, 0,
>> 
>> What's the point of IRQF_SHARED | IRQF_ONESHOT here?
>
> IRQF_SHARED because this interrupt is shared with all the blocks
> which can generate interrupts, i.e. the GPIO contollers.

Why are people still designing hardware with shared interrupts? Shared
interrupts are broken by design and that's well known for decades.

> IRQF_ONESHOT, because its is a threaded interrupt with no primary
> handler. But I just noticed, that regmap-irq will also set the
> IRQF_ONESHOT. But that the commit 09cadf6e088b ("regmap-irq:
> set IRQF_ONESHOT flag to ensure IRQ request") reads like it is
> just there to be sure. So I don't know if it should also be set
> here.

Ok. Wasn't aware of that magic threaded interrupt connection.

Thanks,

        tglx