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Date:   Mon, 31 Jul 2023 10:49:44 +0200
From:   =?iso-8859-2?Q?Micha=B3_Miros=B3aw?= <mirq-linux@rere.qmqm.pl>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc:     Svyatoslav Ryhel <clamor95@gmail.com>,
        Andi Shyti <andi.shyti@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Wolfram Sang <wsa@kernel.org>, linux-i2c@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/2] i2c: Add GPIO-based hotplug gate
Message-ID: <ZMd1qI7RjQhpI8zO@qmqm.qmqm.pl>
References: <20230729160857.6332-1-clamor95@gmail.com>
 <20230729160857.6332-3-clamor95@gmail.com>
 <25858c22-ef92-2136-67ef-0d27364c1600@linaro.org>
 <ZMbcb0yuTz6l6BYh@qmqm.qmqm.pl>
 <b9183dfc-8e8a-9602-f31c-5de9e27acb88@linaro.org>
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On Mon, Jul 31, 2023 at 08:58:14AM +0200, Krzysztof Kozlowski wrote:
> On 30/07/2023 23:55, Micha? Miros?aw wrote:
> > On Sun, Jul 30, 2023 at 10:30:56PM +0200, Krzysztof Kozlowski wrote:
> >> On 29/07/2023 18:08, Svyatoslav Ryhel wrote:
> >>> From: Micha? Miros?aw <mirq-linux@rere.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).

This is no different tham a non-shared interrupt that can be triggered
by the device being removed. Since devres will release the IRQ first,
before freeing the driver data, the interrupt hander will see consistent
driver-internal state. (The difference between remove() and devres
release phase is that for the latter sysfs files are already removed.)

Best Regards
Micha? Miros?aw