Op 22 nov. 2011, om 18:28 heeft Kay Sievers het volgende geschreven: > On Tue, Nov 22, 2011 at 18:10, Martin Langhoff > <martin.langh...@gmail.com> wrote: >> I have just been perusing the systemd code, and wondering whether it >> supports systems that have two RTCs (where usually only one of them is >> the battery-backed clock, the other isn't battery backed but can wake >> the system up). >> >> Background: OLPC's new laptop, XO-1.75, is an ARM SoC that has exactly >> that configuration. Linux kernels from 2.6.32 (and maybe earlier) can >> handle multiple RTCs, and let you configure which one to use to sync >> the clock in early boot (so userland doesn't have to). >> >> I have just reported a related bug in Fedora's initscripts ( >> https://bugzilla.redhat.com/show_bug.cgi?id=756089 ), and a quick >> check of systemd sources hints at similar trouble here... >> >> Two key things seem to be missing: >> >> #1 -- check for the hctosys property. If _any_ rtc present in the >> system has sysfs attribute hctosys == 1, it means that the kernel took >> care of it all, and userland doesn't need to call hwclock, at all. > > Systemd requires that the time was set by the kernel. It does not > support any other config natively, that would be done by plugging-in > hwclock like it was on non-systemd systems. > > The kernel's hctosys is hard coded in the kernel config, right? > >> #2 -- is customary to prefer /dev/rtc if present -- so that we can >> symlink to the right rtc from udev. src/util.c seems to hardcode rtc0. > > Udev does that by default today: > SUBSYSTEM=="rtc", DRIVERS=="rtc_cmos", SYMLINK+="rtc"
That looks to be specific to x86 RTCs, in my case when using the RTC of the
PMIC on omap3/4 I get:
looking at device
'/devices/platform/omap/omap_i2c.1/i2c-1/1-004b/twl_rtc/rtc/rtc0':
KERNEL=="rtc0"
SUBSYSTEM=="rtc"
DRIVER==""
ATTR{name}=="twl_rtc"
ATTR{date}=="2011-11-22"
ATTR{time}=="20:17:03"
ATTR{since_epoch}=="1321993023"
ATTR{max_user_freq}=="64"
ATTR{hctosys}=="1"
ATTR{wakealarm}==""
regards,
Koen
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