linux-kernel - Re: [PATCH v3 2/2] i2c: Add GPIO-based hotplug gate

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Message-ID: <ZMbcb0yuTz6l6BYh@qmqm.qmqm.pl>
Date:   Sun, 30 Jul 2023 23:55:59 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Svyatoslav Ryhel <clamor95@...il.com>
Cc:     Andi Shyti <andi.shyti@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Wolfram Sang <wsa@...nel.org>, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] i2c: Add GPIO-based hotplug gate

On Sun, Jul 30, 2023 at 10:30:56PM +0200, Krzysztof Kozlowski wrote:
> On 29/07/2023 18:08, Svyatoslav Ryhel wrote:
> > From: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> > 
> > Implement driver for hot-plugged I2C busses, where some devices on
> > a bus are hot-pluggable and their presence is indicated by GPIO line.
[...] 
> > +	priv->irq = platform_get_irq(pdev, 0);
> > +	if (priv->irq < 0)
> > +		return dev_err_probe(&pdev->dev, priv->irq,
> > +				     "failed to get IRQ %d\n", priv->irq);
> > +
> > +	ret = devm_request_threaded_irq(&pdev->dev, priv->irq, NULL,
> > +					i2c_hotplug_interrupt,
> > +					IRQF_ONESHOT | IRQF_SHARED,
> 
> Shared IRQ with devm is a recipe for disaster. Are you sure this is a
> shared one? You have a remove() function which also points that it is
> not safe. You can:
> 1. investigate to be sure it is 100% safe (please document why do you
> think it is safe)

Could you elaborate on what is unsafe in using devm with shared
interrupts (as compared to non-shared or not devm-managed)?

The remove function is indeed reversing the order of cleanup. The
shutdown path can be fixed by removing `remove()` and adding
`devm_add_action_or_reset(...deactivate)` before the IRQ is registered.

Best Regards
Michał Mirosław