linux-kernel - Re: [PATCH] i2c: imx: Fix external abort on early interrupt

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Date:   Fri, 12 Jun 2020 12:50:56 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Oleksij Rempel <linux@...pel-privat.de>,
        Wolfram Sang <wsa@...nel.org>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH] i2c: imx: Fix external abort on early interrupt

On 6/12/20 12:44 PM, Krzysztof Kozlowski wrote:
> On Fri, Jun 12, 2020 at 12:34:47PM +0200, Marc Kleine-Budde wrote:
>> On 6/12/20 12:31 PM, Oleksij Rempel wrote:
>>> On Fri, Jun 12, 2020 at 12:21:13PM +0200, Krzysztof Kozlowski wrote:
>>>> On Fri, Jun 12, 2020 at 11:56:04AM +0200, Wolfram Sang wrote:
>>>>> On Fri, Jun 12, 2020 at 11:29:41AM +0200, Krzysztof Kozlowski wrote:
>>>>>> On Fri, Jun 12, 2020 at 11:05:17AM +0200, Wolfram Sang wrote:
>>>>>>> On Wed, Jun 10, 2020 at 03:46:42PM +0200, Krzysztof Kozlowski wrote:
>>>>>>>> If interrupt comes early (could be triggered with CONFIG_DEBUG_SHIRQ),
>>>>>>>
>>>>>>> That code is disabled since 2011 (6d83f94db95c ("genirq: Disable the
>>>>>>> SHIRQ_DEBUG call in request_threaded_irq for now"))? So, you had this
>>>>>>> without fake injection, I assume?
>>>>>>
>>>>>> No, I observed it only after enabling DEBUG_SHIRQ (to a kernel with
>>>>>> some debugging options already).
>>>>>
>>>>> Interesting. Maybe probe was deferred and you got the extra irq when
>>>>> deregistering?
>>>>
>>>> Yes, good catch. The abort happens right after deferred probe exit.  It
>>>> could be then different reason than I thought - the interrupt is freed
>>>> through devm infrastructure quite late.  At this time, the clock might
>>>> be indeed disabled (error path of probe()).
>>
>> From my point of view, the clocks are disabled as Oleksij pointed out, due to
>> RUNTIME_PM at the end of probe():
>>
>>> 	pm_runtime_mark_last_busy(&pdev->dev);
>>> 	pm_runtime_put_autosuspend(&pdev->dev);
> 
> These lines come from regular successful probe path, not deferred error path.
> 
> The clock is indeed disabled but not because of runtime PM, but:
> clk_disable:
> 	clk_disable_unprepare(i2c_imx->clk);

ACK.

I think your analysis is correct: devm for shared IRQs does not work for IP
cores that need enabled clocks for register access.

And from Oleksij's comment we can conclude that runtime_pm and shared IRQ
handlers are also tricky for these IP cores :(

Marc

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