Re: [PATCH 3/3] rtc: rtc-hid-sensor-time; add option hctosys to settime at boot

[Alexander Holler]

Am 23.04.2013 12:13, schrieb Alexander Holler:
> Am 23.04.2013 12:08, schrieb Alexander Holler:
> > 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@xxxxxxxxxxxxx> 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.
>
> Oh, damn. I've forgotten my example above with NTP. In that case setting
> the time when the first RTC appears doesn't work.

So a general solution might be to set the system time when the first RTC 
(or the one mentioned in CONFIG_RTC_HCTOSYS_DEVICE) appears AND nothing 
else did set the time before.

Regards,

Alexander
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