linux-kernel - Re: [PATCH v5 2/2] rtc: omap: Cut down the shutdown time from 2 seconds to 1 sec

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Date:   Tue, 14 Aug 2018 15:24:48 +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 v5 2/2] rtc: omap: Cut down the shutdown time from 2
 seconds to 1 sec



On Tuesday 14 August 2018 02:53 PM, Johan Hovold wrote:
> On Wed, Jul 25, 2018 at 11:21:22AM +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 v5:
>>
>>   * Added an additional check to see if ALARM2 status is not set
>>     before retrying.
>>   * Cleaned up comments
>>   * Also reduced mdelay to 1S lesser as per this commit
>>
>>  drivers/rtc/rtc-omap.c | 28 ++++++++++++++++++----------
>>  1 file changed, 18 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/rtc/rtc-omap.c b/drivers/rtc/rtc-omap.c
>> index 44ff4cc..caa6da6 100644
>> --- a/drivers/rtc/rtc-omap.c
>> +++ b/drivers/rtc/rtc-omap.c
>> @@ -421,12 +421,6 @@ static int omap_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
>>   * The RTC can be used to control an external PMIC via the pmic_power_en pin,
>>   * which can be configured to transition to OFF on ALARM2 events.
>>   *
>> - * Notes:
>> - * The two-second alarm offset is the shortest offset possible as the alarm
>> - * registers must be set before the next timer update and the offset
>> - * calculation is too heavy for everything to be done within a single access
>> - * period (~15 us).
>> - *
>>   * Called with local interrupts disabled.
>>   */
>>  static void omap_rtc_power_off(void)
>> @@ -435,17 +429,20 @@ static void omap_rtc_power_off(void)
>>  	struct rtc_time tm;
>>  	unsigned long now;
>>  	u32 val;
>> +	int seconds;
> 
> Nit: I'd place this above val to maintain the reverse xmas-tree style.

okay

> 
>>  
>>  	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:
>> +	/* 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");
>> @@ -470,14 +467,25 @@ 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);
>> +
>> +	/*
>> +	 * first check if ALARM2 has fired, if not then check if
>> +	 * our calculations started right before the rollover, try again
>> +	 * in case of rollover
>> +	 */
> 
> This is unnecessarily verbose; I'd rephrase it as something like:
> 
> 	/* Retry in case roll over happened before alarm was armed. */

Okay

> 
>> +	if (!(OMAP_RTC_STATUS_ALARM2 && rtc_read(omap_rtc_power_off_rtc,
>> +						 OMAP_RTC_STATUS_REG)) &&
>> +	    seconds != rtc_read(omap_rtc_power_off_rtc, OMAP_RTC_SECONDS_REG))
>> +		goto again;
> 
> And this is clearly broken. First, you use boolean && instead of the &
> bit operation.

Ah my bad. I will fix it.

> 
> Second, you need to check the status register *after* checking for
> roll-over, as I already mentioned.
> 
> Also, use the rtc pointer rather than omap_rtc_power_off_rtc, which will
> allow for more readable code.

Okay

> 
> I also strongly suggest you split the conditional, and use val to store
> the status register value, that is:
> 
> 	if (rtc_read(rtc, OMAP_RTC_SECONDS_REG) != seconds) {
> 		val = rtc_read(rtc, OMAP_RTC_STATUS_REG);
> 		if (!(val & OMAP_RTC_STATUS_ALARM2))
> 			goto again;
> 	}
> 
>> +
>>  	rtc->type->lock(rtc);
>>  
>>  	/*
>> -	 * Wait for alarm to trigger (within two seconds) and external PMIC to
>> +	 * Wait for alarm to trigger (within one second) and external PMIC to
>>  	 * power off the system. Add a 500 ms margin for external latencies
>>  	 * (e.g. debounce circuits).
>>  	 */
>> -	mdelay(2500);
>> +	mdelay(1500);
>>  }
>>  
>>  static const struct rtc_class_ops omap_rtc_ops = {
> 
> Johan
>