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

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Message-ID: <b9183dfc-8e8a-9602-f31c-5de9e27acb88@linaro.org>
Date:   Mon, 31 Jul 2023 08:58:14 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        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 30/07/2023 23:55, Michał Mirosław wrote:
> 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.

Shared interrupt might be triggered easily by other device between
remove() and irq release function (devm_free_irq() or whatever it is
called).

Best regards,
Krzysztof