Messages in this thread | | | Date | Tue, 23 Apr 2013 12:08:12 +0200 | From | Alexander Holler <> | Subject | Re: [PATCH 3/3] rtc: rtc-hid-sensor-time; add option hctosys to set time at boot |
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Am 23.04.2013 10:51, schrieb Alexander Holler: > Am 23.04.2013 01:38, schrieb Andrew Morton: >> On Fri, 19 Apr 2013 17:14:12 +0200 Alexander Holler >> <holler@ahsoftware.de> wrote: >> >>> drivers/rtc/hctosys (CONFIG_RTC_HCTOSYS) doesn't work for >>> rtc-hid-sensor-time because it will be called in late_init, and thus >>> before >>> rtc-hid-sensor-time gets loaded. >> >> Isn't that true of all RTC drivers which are built as modules? There's >> nothing special about hid-sensor-time here? >> >> I assume the standard answer here is "your RTC driver should be built >> into vmlinux". If we wish to make things work for modular RTC drivers >> then we should find a solution which addresses *all* RTC drivers? > > No. I having rtc-hid-sensor-time, hid-sensor-hub (and USB) statically > linked in doesn't help. Here is what happens here with such an > configuration: > > -- > [ 7.638970] drivers/rtc/hctosys.c: unable to open rtc device (rtc0) > [ 7.645639] Waiting 180sec before mounting root device... > [ 16.598759] HID-SENSOR-2000a0 HID-SENSOR-2000a0.0: rtc core: > registered hid-sensor-time as rtc0 > [ 16.608712] HID-SENSOR-2000a0 HID-SENSOR-2000a0.0: hctosys: setting > system clock to 2013-04-19 16:45:06 UTC (1366389906) > -- > > I havent't looked in detail at why rtc-hid-sensor-time gets loaded that > late, but I assume it's because the USB stack (and/or the device or the > communication inbetween) needs some time (and I assume that's why > rootwait and rootdelay got invented too). > >> >>> To set the time through rtc-hid-sensor-time >>> at startup, the module now checks by default if the system time is >>> before >>> 1970-01-02 and sets the system time (once) if this is the case. >>> >>> To disable this behaviour, set the module option hctosys to zero, >>> e.g. by >>> using rtc-hid-sensor-time.hctosys=0 at the kernel command line if the >>> driver is statically linked into the kernel. >> >> Is a bit hacky, no? > > I didn't have any other idea to prevent an USB (or any other > hot-pluggable HID) device to change the time while still beeing able (by > default) to set the time by such an device at boot. But I'm open to > suggestions. (E.g. one of the scenarios I want to prevent is, that a > computer gets it's time by NTP and someone is able to change the time > later on by simply plugging in some HID device.) >
To add something more: I use the system time as a bool "time_was_set_once" and have choosen one day just in case something needs really long to boot (e.g. because of some lengthy fsck or whatever else).
A solution to both problems might be to change the logic for hctosys completly to read the time when the first RTC device appears (or when the device mentioned in CONFIG_RTC_HCTOSYS_DEVICE appears). But that would require a change to hctosys or the RTC subsystem, which would involve more patches and discussion. As rtc-hid-sensor-time currently seems to be the only RTC with the above problems, I've gone the easy route and only modified this driver.
Regards,
Alexander
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