Re: TS-219 RTC issue with Debian Buster

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

Hello Oliver,

I added the RTC maintainers and list to Cc.

On Tue, Jul 23, 2019 at 05:30:48PM +0200, Oliver Hartkopp wrote:
> I upgraded my TS-219 to Debian Buster with Kernel 4.19.0-5-marvell.
> 
> They use dtbs/4.19.0-5-marvell/./kirkwood-ts219-6282.dtb
> 
> Unfortunately the RTC doesn't seem to work.
> 
> root@xxxxx:~# hwclock -v --test
> hwclock from util-linux 2.33.1
> System Time: 1563296223.425648
> Trying to open: /dev/rtc0
> Using the rtc interface to the clock.
> Last drift adjustment done at 1563291472 seconds after 1969
> Last calibration done at 1563291472 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> Waiting for clock tick...
> hwclock: select() to /dev/rtc0 to wait for clock tick timed out
> ...synchronization failed
> Test mode: nothing was changed.
> With strace the clock tick problem looks like this:
> 
> write(1, "Waiting for clock tick...\n", 26Waiting for clock tick...
> ) = 26
> ioctl(4, RTC_UIE_ON)                    = 0
> _newselect(5, [4], NULL, NULL, {tv_sec=10, tv_usec=0}) = 0 (Timeout)
> write(2, "hwclock: ", 9hwclock: )                = 9
> write(2, "select() to /dev/rtc0 to wait fo"..., 54select() to /dev/rtc0 to
> wait for clock tick timed out) = 54
> write(2, "\n", 1)                       = 1
> ioctl(4, PHN_NOT_OH or RTC_UIE_OFF)     = 0

Maybe rtc-mv should set uie_unsupported if no irq is aquired? 

> It looks the same with
> 
> # hwclock --hctosys
> hwclock: select() to /dev/rtc0 to wait for clock tick timed out

hwclock (from util-linux) is being stupid here. The tradtional RTC on
the x86 platform has a resolution of 1s only and if you set it the next
increment is 1 second after the last increment instead of 1 second after
the new time was set. So hwclock waits for an update event and then sets
the new time (in some cases to a tad later than requested) to ensure the
PC clock is off by less than half a second. For most (if not all) other
RTCs this is wrong and still worse if the RTC in question doesn't
support UIE.

> I wonder whether the problem comes from a missing interrupt assignment
> 
> rtc: rtc@10300 {
>              compatible = "marvell,kirkwood-rtc", "marvell,orion-rtc";
>              reg = <0x10300 0x20>;
>              interrupts = <53>;            <- HERE!?!
>              clocks = <&gate_clk 7>;
>                };
> 
> ... I found in linux/arch/arm/boot/dts/kirkwood-6282.dtsi ?!?
> 
> In /proc/interrupts there's no rtc assigned to an interrupt 53.

What is the output of dmesg | grep 10300 ?
 
> Accessing the rtc values (time/date) via /sys/class/rtc/rtc0 entries works
> well and setting the date/time via "hwclock --systohc" does its job too. So
> I2C and the rtc_s35390a driver seem to work so far.

You're not using the s35390a driver, do you?
 
> Any ideas why hwclock fails to work properly?

Try if 

	busybox hwclock 

works better for you. At least this one doesn't have this strange PC
quirk.
 
Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |