linux-kernel - Re: [PATCH V1] rtc: da9053: fix access ordering error during RTC interrupt at system power on

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Date:	Tue, 19 Apr 2016 00:34:14 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Steve Twiss <stwiss.opensource@...semi.com>
Cc:	LINUXKERNEL <linux-kernel@...r.kernel.org>,
	RTC-LINUX <rtc-linux@...glegroups.com>,
	Support Opensource <support.opensource@...semi.com>
Subject: Re: [PATCH V1] rtc: da9053: fix access ordering error during RTC
 interrupt at system power on

On 14/04/2016 at 12:04:54 +0100, Steve Twiss wrote :
> From: Steve Twiss <stwiss.opensource@...semi.com>
> 
> This fix alters the ordering of the IRQ and device registrations in the RTC
> driver probe function. This change will apply to the RTC driver that supports
> both DA9052 and DA9053 PMICs.
> 
> A problem could occur with the existing RTC driver if:
> 
> A system is started from a cold boot using the PMIC RTC IRQ to initiate a
> power on operation. For instance, if an RTC alarm is used to start a
> platform from power off.
> The existing driver IRQ is requested before the device has been properly
> registered.
> 
> i.e.
> ret = da9052_request_irq()
> comes before
> rtc->rtc = devm_rtc_device_register();
> 
> In this case, an interrupt exists before the device has been registered and
> the IRQ handler can be called immediately: this can happen be before the
> memory for rtc->rtc has been allocated. The IRQ handler da9052_rtc_irq()
> contains the function call:
> 
> rtc_update_irq(rtc->rtc, 1, RTC_IRQF | RTC_AF);
> 
> which in turn tries to access the unavailable rtc->rtc.
> 
> The fix is to reorder the functions inside the RTC probe. The IRQ is
> requested after the RTC device resource has been registered so that
> da9052_request_irq() is the last thing to happen.
> 
> Signed-off-by: Steve Twiss <stwiss.opensource@...semi.com>
> 
Applied, thanks.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com