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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 19 Jul 2018 17:23:16 +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 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.

> 
> Add a newline here too.

Okay

> 
>>  	rtc->type->lock(rtc);
>>  
>>  	/*
> 
> Thanks,
> Johan
>