Re: [rtc-linux] [PATCH] rtc: ds1307.c: add support for the DT property 'wakeup-source'

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

Hi,

On 22/01/2016 at 16:35:39 +0100, Michael Lange wrote :
> >I don't think setting uie_unsupported is necessary because the alarm
> >functions will fail anyway. What kind of issue did you have?
> >
> 
> Tested today in the morning, before I had to go to work, the wakealarm
> and the 'hwclock' binary with and without to set uie_unsupported in
> rtc-ds1307.
> 
> 
> With uie_unsupported = 1:
> 
> The wakealarm is working, as expected:
>   root@rbpi2 michael # echo +60 > /sys/class/rtc/rtc0/wakealarm
>   root@rbpi2 michael # shutdown -h now
> ... wait, and the Raspberry comes up.
> 
> The hwclock binary is also working:
> root@rbpi2 michael # LC_ALL=C hwclock -D -s
> hwclock from util-linux 2.27.1
> Using the /dev interface to the clock.
> Last drift adjustment done at 1453438995 seconds after 1969
> Last calibration done at 1453438995 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> Waiting for clock tick...
> /dev/rtc does not have interrupt functions. Waiting in loop for time from
> /dev/rtc to change
> ...got clock tick
> Time read from Hardware Clock: 2016/01/22 05:05:29
> Hw clock time : 2016/01/22 05:05:29 = 1453439129 seconds since 1969
> Time since last adjustment is 134 seconds
> Calculated Hardware Clock drift is 0.000000 seconds
> Calling settimeofday:
>     tv.tv_sec = 1453439129, tv.tv_usec = 0
>     tz.tz_minuteswest = -60
> 
> root@rbpi2 michael # LC_ALL=C hwclock -D -w
> hwclock from util-linux 2.27.1
> Using the /dev interface to the clock.
> Last drift adjustment done at 1453438995 seconds after 1969
> Last calibration done at 1453438995 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> Waiting for clock tick...
> /dev/rtc does not have interrupt functions. Waiting in loop for time from
> /dev/rtc to change
> ...got clock tick
> Time read from Hardware Clock: 2016/01/22 05:05:48
> Hw clock time : 2016/01/22 05:05:48 = 1453439148 seconds since 1969
> Time since last adjustment is 153 seconds
> Calculated Hardware Clock drift is 0.000000 seconds
> missed it - 1453439148.507319 is too far past 1453439148.500000 (0.007319 >
> 0.001000)
> 1453439149.500000 is close enough to 1453439149.500000 (0.000000 < 0.002000)
> Set RTC to 1453439149 (1453439148 + 1; refsystime = 1453439148.000000)
> Setting Hardware Clock to 05:05:49 = 1453439149 seconds since 1969
> ioctl(RTC_SET_TIME) was successful.
> Not adjusting drift factor because the --update-drift option was not used.
> 
> 
> 
> After that, the kernel was compiled without setting ui_unsupported in
> rtc-ds1307.c, and I got the following:
> 
> root@rbpi2 michael # LC_ALL=C hwclock -D -s
> hwclock from util-linux 2.27.1
> Using the /dev interface to the clock.
> Last drift adjustment done at 1453439148 seconds after 1969
> Last calibration done at 1453439148 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> Waiting for clock tick...
> select() to /dev/rtc to wait for clock tick timed out...synchronization
> failed
> 
> The wakealarm is still working fine.
> 

Ok, thanks, I'll try to reproduce on one of my boards but this shouldn't
happen. My current understanding is that uie_unsupported should only be
set when the alarm function is supported but the resolution is higher
than a second (usually a minute).

> 
> The ds1337 on the Witty Pi extension board is connected to the i2c pins on
> the Raspberry and the alarm pin is probably connected to a mosfet (F7319)
> on this board, that powers up the Raspberry through the 5V-Pin on the
> 40pin-header.
> 
> But I'm not sure at all with the mosfet ... I'm not a electronics technician
> ...
> 

I don't think it actually matter :)

> 
> 
> An other example for a RTC and no IRQ to the CPU/Soc is in the rtc-isl12057
> http://lxr.free-electrons.com/source/drivers/rtc/rtc-isl12057.c#L460
> http://lxr.free-electrons.com/source/drivers/rtc/rtc-isl12057.c#L604
> 
> Without this patch the ds1337 got no wakealarm sysfs entry.
> 

Sure, I understand the rationale behind the patch. I'll take it as is
and I'll investigate the uie_unsupported oddity.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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