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authorDavid Brownell <david-b@pacbell.net>2007-05-08 00:33:42 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-05-08 11:15:18 -0700
commit7ca1d488ffe4817adaba61cc05b972782f7d3f91 (patch)
tree97fee4d2ddbc5be5265d99f5825e902f7a9262c1 /drivers/rtc/Kconfig
parentcd9662094edf4173e87f0452e57e4eacc228f8ff (diff)
downloadop-kernel-dev-7ca1d488ffe4817adaba61cc05b972782f7d3f91.zip
op-kernel-dev-7ca1d488ffe4817adaba61cc05b972782f7d3f91.tar.gz
rtc: suspend()/resume() restores system clock
RTC class suspend/resume support, re-initializing the system clock on resume from the clock used to initialize it at boot time. - The reinit-on-resume is hooked to the existing RTC_HCTOSYS config option, on the grounds that a clock good enough for init must also be good enough for re-init. - Inlining a version of the code used by ARM, to save and restore the delta between a selected RTC and the current system wall-clock time. - Removes calls to that ARM code from AT91, OMAP1, and S3C RTCs. This means that systems using those RTCs across suspend/resume will likely want to change their kernel configs to enable RTC_HCTOSYS. If HCTOSYS isn't using a second RTC (with battery?), this changes the system's initial date from Jan 1970 to the epoch this hardware uses: 1998 for AT91, 2000 for OMAP1 (assuming no split power mode), etc. This goes on top of the patch series removing "struct class_device" usage from the RTC framework. That's all needed for class suspend()/resume(). Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Acked-by: Greg Kroah-Hartman <gregkh@suse.de> Acked-By: Alessandro Zummo <a.zummo@towertech.it> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/rtc/Kconfig')
-rw-r--r--drivers/rtc/Kconfig24
1 files changed, 17 insertions, 7 deletions
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index ec33ee8..a53ef4d 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -21,21 +21,31 @@ config RTC_CLASS
will be called rtc-class.
config RTC_HCTOSYS
- bool "Set system time from RTC on startup"
+ bool "Set system time from RTC on startup and resume"
depends on RTC_CLASS = y
default y
help
- If you say yes here, the system time will be set using
- the value read from the specified RTC device. This is useful
- in order to avoid unnecessary fsck runs.
+ If you say yes here, the system time (wall clock) will be set using
+ the value read from a specified RTC device. This is useful to avoid
+ unnecessary fsck runs at boot time, and to network better.
config RTC_HCTOSYS_DEVICE
- string "The RTC to read the time from"
+ string "RTC used to set the system time"
depends on RTC_HCTOSYS = y
default "rtc0"
help
- The RTC device that will be used as the source for
- the system time, usually rtc0.
+ The RTC device that will be used to (re)initialize the system
+ clock, usually rtc0. Initialization is done when the system
+ starts up, and when it resumes from a low power state.
+
+ This clock should be battery-backed, so that it reads the correct
+ time when the system boots from a power-off state. Otherwise, your
+ system will need an external clock source (like an NTP server).
+
+ If the clock you specify here is not battery backed, it may still
+ be useful to reinitialize system time when resuming from system
+ sleep states. Do not specify an RTC here unless it stays powered
+ during all this system's supported sleep states.
config RTC_DEBUG
bool "RTC debug support"
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