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 17:52:17 +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 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:
>>> Cut down the shutdown time from 2 seconds to 1 sec. In case of roll
>>> over try again.
>>>
>>> Signed-off-by: Keerthy <j-keerthy@...com>
>>> ---
>>>
>>> Changes in v4:
>>>
>>>   * Fixed a compilation issue.
>>>   * Extended the roll over check post interrupt programming.
>>>
>>>  drivers/rtc/rtc-omap.c | 13 +++++++++++--
>>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/rtc/rtc-omap.c b/drivers/rtc/rtc-omap.c
>>> index 323ff55..88da927 100644
>>> --- a/drivers/rtc/rtc-omap.c
>>> +++ b/drivers/rtc/rtc-omap.c
>>
>> First, the comment above this function would need to be updated as part
>> of this patch as it refers to the two-second alarm offset.
> 
> Yes, will change that.
> 
>>
>>> @@ -435,17 +435,23 @@ static void omap_rtc_power_off(void)
>>>  	struct rtc_time tm;
>>>  	unsigned long now;
>>>  	u32 val;
>>> +	int seconds;
>>>  
>>>  	rtc->type->unlock(rtc);
>>>  	/* enable pmic_power_en control */
>>>  	val = rtc_readl(rtc, OMAP_RTC_PMIC_REG);
>>>  	rtc_writel(rtc, OMAP_RTC_PMIC_REG, val | OMAP_RTC_PMIC_POWER_EN_EN);
>>>  
>>> -	/* set alarm two seconds from now */
>>> +again:
>>> +	/* Clear any existing ALARM2 event */
>>> +	rtc_writel(rtc, OMAP_RTC_STATUS_REG, OMAP_RTC_STATUS_ALARM2);
>>
>> Why is this needed? Any pending interrupt is cleared at probe, and a
>> previous attempt to set the alarm really led to the alarm going off, why
>> would we retry?
> 
> Yes this is not needed.
> 
>>
>>> +
>>> +	/* set alarm one second from now */
>>>  	omap_rtc_read_time_raw(rtc, &tm);
>>> +	seconds = tm.tm_sec;
>>>  	bcd2tm(&tm);
>>>  	rtc_tm_to_time(&tm, &now);
>>> -	rtc_time_to_tm(now + 2, &tm);
>>> +	rtc_time_to_tm(now + 1, &tm);
>>>  
>>>  	if (tm2bcd(&tm) < 0) {
>>>  		dev_err(&rtc->rtc->dev, "power off failed\n");
>>> @@ -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);
>>
>> Add a newline here.
> 
> Okay
> 
>>
>>> +	/* Our calculations started right before the rollover, try again */
>>
>> Nit: use all lower case unless writing full sentences, which also
>> matches most of the other comments in this file.
> 
> okay
> 
>>
>>> +	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?
> 
> 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.

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.

> 
>>
>> Add a newline here too.
> 
> Okay
> 
>>
>>>  	rtc->type->lock(rtc);
>>>  
>>>  	/*
>>
>> Thanks,
>> Johan
>>
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