linux-kernel - Re: [PATCH v4 1/4] rtc: omap: Cut down the shutdown time from 2 seconds to 1 sec

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Date:   Thu, 19 Jul 2018 18:16:56 +0530
From:   Keerthy <j-keerthy@...com>
To:     Johan Hovold <johan@...nel.org>
CC:     <a.zummo@...ertech.it>, <alexandre.belloni@...tlin.com>,
        <t-kristo@...com>, <linux-rtc@...r.kernel.org>,
        <linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/4] rtc: omap: Cut down the shutdown time from 2
 seconds to 1 sec



On Thursday 19 July 2018 06:06 PM, Johan Hovold wrote:
> On Thu, Jul 19, 2018 at 05:52:17PM +0530, Keerthy wrote:
>> On Thursday 19 July 2018 05:23 PM, Keerthy wrote:
>>> On Thursday 19 July 2018 03:32 PM, Johan Hovold wrote:
>>>> On Thu, Jul 12, 2018 at 10:37:37AM +0530, Keerthy wrote:
> 
>>>>> @@ -470,6 +476,9 @@ static void omap_rtc_power_off(void)
>>>>>  	val = rtc_read(rtc, OMAP_RTC_INTERRUPTS_REG);
>>>>>  	rtc_writel(rtc, OMAP_RTC_INTERRUPTS_REG,
>>>>>  			val | OMAP_RTC_INTERRUPTS_IT_ALARM2);
> 
>>>>> +	/* Our calculations started right before the rollover, try again */
> 
>>>>> +	if (seconds != rtc_read(omap_rtc_power_off_rtc, OMAP_RTC_SECONDS_REG))
>>>>> +		goto again;
>>>>
>>>> Here the alarm may have gone off as part of the roll over, in which case
>>>> you shouldn't retry.
>>>
>>> Ex: We programmed at Sec = 2 and we expect ALARM2 to fire at sec = 3.
>>>
>>> In the event of Roll over before setting the
>>> OMAP_RTC_INTERRUPTS_IT_ALARM2 bit in the OMAP_RTC_INTERRUPTS_REG will we
>>> not miss the ALARM2 event? Then poweroff would fail right?
> 
> Right, that would fail.
> 
>>> Hence the attempt to retry the next second. This sequence would begin
>>> right at the beginning of a new second and we expect the full sequence
>>> to get over without having to retry again.
>>>
>>> Hope i am clear.
> 
> Yes, sure, but my point is that could end up retrying also after the
> alarm has fired correctly (e.g. due to latencies in turning of the
> power)>
> It may be enough to check OMAP_RTC_STATUS_REG before retrying.

Ah okay. Yes this makes sense. I will use the status to retry.

> 
>> I tried to program the interrupt for the same second on the hardware and
>> it does not fire. So to take care of roll over corner case one attempt
>> to retry is needed.
> 
> Yes, that's expected.
> 
> Thanks,
> Johan
>