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

[Alexander Holler <holler@ahsoftware.de>]

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@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.
>
> 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