Re: [systemd-devel] Support machines with multiple RTCs?
On Wed, Nov 23, 2011 at 04:04, Martin Langhoff martin.langh...@gmail.com wrote: On Nov 22, 2011 5:58 PM, Kay Sievers kay.siev...@vrfy.org wrote: On Tue, Nov 22, 2011 at 23:42, Martin Langhoff martin.langh...@gmail.com wrote: On Tue, Nov 22, 2011 at 3:21 PM, Kay Sievers kay.siev...@vrfy.org wrote: Yeah, that's intentional. Udev on other platforms can't know which rtc should be the preferred one. Well, now you can: if it says hctosys == 1, it means that the kernel config told it to pick that one, and that it's sync'd the system time to it. You have rtc1 set in the kernel config for your box? Correct. And rtc0 is only good for rtcwake -- won't hold real clock time, because it isn't battery-backed. My box is the XO-1.75 platform, of which we expect a few million will be produced starting soon. Future kernels may bring them up in different order, but that's a different pile of pain. This link is mainly for backwards compat, because in earlier days it was a real kernel device. Well, the symlink has a very practical use! If you have several RTCs, you can use udev to symlink rtc to it, and it gets htclock to DTRT. On our XO-1.75, the real rtc is rtc1. Next, we got to get src/utils.c to prefer rtc if it finds it ;-) I guess udev should claim /dev/rtc for the rtc device that has hctosys == 1 set? Yep. It's a trivial udev rule, perhaps belongs to Fedora's initscripts? Nah, 'initscripts' needs a radical diet, not more random stuff in it. :) Todo lists are there to remember things. Seems that worked well in this case. :) Here is the systemd fix: http://cgit.freedesktop.org/systemd/systemd/commit/?id=51122dc9e36cdafe76a07d1ddf1a3a7e4726bb7b and the udev fix: http://git.kernel.org/?p=linux/hotplug/udev.git;a=commitdiff;h=6102188c93e55eba1b5dad54d27ea1ac2e8c7e73 Both use the 'system rtc' now. Kay ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Support machines with multiple RTCs?
On Tue, Nov 22, 2011 at 12:28 PM, Kay Sievers kay.siev...@vrfy.org wrote: #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. Cool. That's very appropriate given a minimally modern linux kernel... The kernel's hctosys is hard coded in the kernel config, right? It is set by the kernel to 1, only when CONFIG_RTC_HCTOSYS_DEVICE is set, and when the device is the device named in this config var. If you don't have CONFIG_RTC_HCTOSYS_DEVICE, then the kernel won't sync system time during boot, and your rtc device will have hctosys==0. So if systemd counts on the kernel to set system time during boot, then you already depend on CONFIG_RTC_HCTOSYS_DEVICE, and you should be all set :-) #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 Yes, but that means that it expects other programs to first try to open /dev/rtc . So to complete the picture, I think src/util.c should try /dev/rtc first :-) If possible, we could invent a /dev/rtc-systemtime symlink and use that, if its not needed during bootup before udev is started and has created the symlink? that be the same as /dev/rtc I think... so no need for it that I can see. m -- martin.langh...@gmail.com mar...@laptop.org -- Software Architect - OLPC - ask interesting questions - don't get distracted with shiny stuff - working code first - http://wiki.laptop.org/go/User:Martinlanghoff ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Support machines with multiple RTCs?
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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Re: [systemd-devel] Support machines with multiple RTCs?
On Tue, Nov 22, 2011 at 21:18, Koen Kooi k...@dominion.thruhere.net wrote: Op 22 nov. 2011, om 18:28 heeft Kay Sievers het volgende geschreven: On Tue, Nov 22, 2011 at 18:10, Martin Langhoff #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== Yeah, that's intentional. Udev on other platforms can't know which rtc should be the preferred one. This link is mainly for backwards compat, because in earlier days it was a real kernel device. Kay ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Support machines with multiple RTCs?
On Tue, Nov 22, 2011 at 3:21 PM, Kay Sievers kay.siev...@vrfy.org wrote: Yeah, that's intentional. Udev on other platforms can't know which rtc should be the preferred one. Well, now you can: if it says hctosys == 1, it means that the kernel config told it to pick that one, and that it's sync'd the system time to it. This link is mainly for backwards compat, because in earlier days it was a real kernel device. Well, the symlink has a very practical use! If you have several RTCs, you can use udev to symlink rtc to it, and it gets htclock to DTRT. On our XO-1.75, the real rtc is rtc1. Next, we got to get src/utils.c to prefer rtc if it finds it ;-) m -- martin.langh...@gmail.com mar...@laptop.org -- Software Architect - OLPC - ask interesting questions - don't get distracted with shiny stuff - working code first - http://wiki.laptop.org/go/User:Martinlanghoff ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Support machines with multiple RTCs?
On Tue, Nov 22, 2011 at 23:42, Martin Langhoff martin.langh...@gmail.com wrote: On Tue, Nov 22, 2011 at 3:21 PM, Kay Sievers kay.siev...@vrfy.org wrote: Yeah, that's intentional. Udev on other platforms can't know which rtc should be the preferred one. Well, now you can: if it says hctosys == 1, it means that the kernel config told it to pick that one, and that it's sync'd the system time to it. You have rtc1 set in the kernel config for your box? This link is mainly for backwards compat, because in earlier days it was a real kernel device. Well, the symlink has a very practical use! If you have several RTCs, you can use udev to symlink rtc to it, and it gets htclock to DTRT. On our XO-1.75, the real rtc is rtc1. Next, we got to get src/utils.c to prefer rtc if it finds it ;-) I guess udev should claim /dev/rtc for the rtc device that has hctosys == 1 set? Kay ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
