linux-kernel - Re: [PATCH V1] drivers/rtc: da9052: ALARM causes interrupt storm

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Message-Id: <20140502130942.490ca884c0a1f4a2c47de150@linux-foundation.org>
Date:	Fri, 2 May 2014 13:09:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Opensource [Anthony Olech]" <anthony.olech.opensource@...semi.com>
Cc:	Alessandro Zummo <a.zummo@...ertech.it>,
	Support Opensource <support.opensource@...semi.com>,
	<linux-kernel@...r.kernel.org>, <rtc-linux@...glegroups.com>,
	David Dajun Chen <david.chen@...semi.com>
Subject: Re: [PATCH V1] drivers/rtc: da9052: ALARM causes interrupt storm

On Wed, 2 Apr 2014 12:45:38 +0100 "Opensource [Anthony Olech]" <anthony.olech.opensource@...semi.com> wrote:

> Setting the alarm to a time not on a minute boundary results in repeated
> interrupts being generated by the DA9052/3 PMIC device until the kernel
> RTC core sees that the alarm has rung. Sometimes the number and frequency
> of interrupts can cause the kernel to disable the IRQ line used by the
> DA9052/3 PMIC with disasterous consequences. This patch fixes the problem.
> 
> Even though the DA9052/3 PMIC is capable generating periodic interrupts,
> ie TICKS, the method used to distinguish RTC_AF from RTC_PF events was
> flawed and can not work in conjunction with the regmap_irq kernel core.
> Thus that flawed detection has also been removed by the DA9052/3 PMIC RTC
> driver's irq handler, so that it no longer reports the wrong type of event
> to the kernel RTC core.
> 
> The internal static functions within the DA9052/3 PMIC RTC driver have
> been changed to pass the 'da9052_rtc' structure instead of the 'da9052'
> because there is no backwards pointer from the 'da9052' structure.
> 
> Signed-off-by: Anthony Olech <anthony.olech.opensource@...semi.com>
> ---
> 
> This patch is relative to linux-next repository tag next-20140402
> 
> This patch fixes the three issues described above. The first is serious
> because usiing the RTC alarm set to a non minute boundary will eventually
> cause all component drivers that depend on the interrupt line to fail. The
> solution adopted is to round up to alarm time to the next highest minute.
> 
> The second bug, reporting a RTC_PF event instead of an RTC_AF event turns
> out to not matter with the current implementation of the kernel RTC core
> as it seems to ignore the event type. However, should that change in the
> future it is better to fix the issue now and not have 'problems waiting to
> happen'
> 
> The third set of changes are to make the da9052_rtc structure available
> to all the local internal functions in the driver. This was done during
> testing so that diagnostic data could be stored there. Should the solution
> to the first issue be found not acceptable, then the alternative of using
> the TICKS interrupt at the fixed one second interval in order to step to
> the exact second of the requested alarm requires an extra (alarm time)
> piece of data to be stored. In devices that use the alarm function to wake
> up from sleep, accuracy to the second will result in the device being
> awake for up to nearly a minute longer than expected.

The above three paragraphs contained important info which is
appropriate to the formal patch changelog.

>
> ...
>
> @@ -261,7 +271,7 @@ static struct platform_driver da9052_rtc_driver = {
>  
>  module_platform_driver(da9052_rtc_driver);
>  
> -MODULE_AUTHOR("David Dajun Chen <dchen@...semi.com>");
> +MODULE_AUTHOR("Anthony Olech <Anthony.Olech@...semi.com>");
>  MODULE_DESCRIPTION("RTC driver for Dialog DA9052 PMIC");
>  MODULE_LICENSE("GPL");
>  MODULE_ALIAS("platform:da9052-rtc");

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