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3dcad5ff08
linux/drivers/rtc
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John Stultz 3dcad5ff08 rtc: Avoid accumulating time drift in suspend/resume 
Because the RTC interface is only a second granular interface,
each time we read from the RTC for suspend/resume, we introduce a
half second (on average) of error.

In order to avoid this error accumulating as the system is suspended
over and over, this patch measures the time delta between the RTC
and the system CLOCK_REALTIME.

If the delta is less then 2 seconds from the last suspend, we compensate
by using the previous time delta (keeping it close). If it is larger
then 2 seconds, we assume the clock was set or has been changed, so we
do no correction and update the delta.

Note: If NTP is running, ths could seem to "fight" with the NTP corrected
time, where as if the system time was off by 1 second, and NTP slewed the
value in, a suspend/resume cycle could undo this correction, by trying to
restore the previous offset from the RTC. However, without this patch,
since each read could cause almost a full second worth of error, its
possible to get almost 2 seconds of error just from the suspend/resume
cycle alone, so this about equal to any offset added by the compensation.

Further on systems that suspend/resume frequently, this should keep time
closer then NTP could compensate for if the errors were allowed to
accumulate.

Credits to Arve Hjønnevåg for suggesting this solution.

This patch also improves some of the variable names and adds more clear
comments.

CC: Arve Hjønnevåg <arve@android.com>
CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
2011-06-21 16:55:39 -07:00
..
class.c rtc: Avoid accumulating time drift in suspend/resume 2011-06-21 16:55:39 -07:00
hctosys.c rtc/hctosys: only claim the RTC provided the system time if it did 2010-03-12 15:52:28 -08:00
interface.c rtc: Staticize non-exported __rtc_set_alarm() 2011-06-01 19:29:40 -07:00
Kconfig unicore32: move rtc-puv3.c to drivers/rtc directory 2011-06-09 16:15:24 +08:00
Makefile unicore32: move rtc-puv3.c to drivers/rtc directory 2011-06-09 16:15:24 +08:00
rtc-88pm860x.c mfd: Add rtc support to 88pm860x 2011-05-26 19:45:34 +02:00
rtc-ab3100.c drivers/rtc/rtc-ab3100.c: add missing platform_set_drvdata() in ab3100_rtc_probe() 2010-09-22 17:22:39 -07:00
rtc-ab8500.c mfd: Align ab8500 with the abx500 interface 2010-10-29 00:29:19 +02:00
rtc-at32ap700x.c RTC: Convert rtc drivers to use the alarm_irq_enable method 2011-02-03 13:02:35 -08:00
rtc-at91rm9200.c Fix common misspellings 2011-03-31 11:26:23 -03:00
rtc-at91sam9.c RTC: Clean out UIE icotl implementations 2011-03-09 11:24:54 -08:00
rtc-au1xxx.c
rtc-bfin.c Merge branch 'fortglx/39/tip/timers/rtc' of git://git.linaro.org/people/jstultz/linux into timers/urgent 2011-04-13 01:54:09 +02:00
rtc-bq32k.c rtc: add driver for BQ32000 I2C RTC 2009-12-16 07:20:00 -08:00
rtc-bq4802.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
rtc-cmos.c Merge branch 'x86-platform-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-03-15 20:01:36 -07:00
rtc-coh901331.c rtc: fix coh901331 startup crash 2011-04-20 18:46:56 +02:00
rtc-core.h
rtc-davinci.c rtc: davinci: Initialize drvdata before registering device 2011-05-06 17:41:06 -07:00
rtc-dev.c rtc: Fix ioctl error path return 2011-06-01 19:29:39 -07:00
rtc-dm355evm.c
rtc-ds1216.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
rtc-ds1286.c rtc: ds1286: Initialize drvdata before registering device 2011-05-06 17:42:47 -07:00
rtc-ds1302.c sh: mach-snapgear: Kill off machtype, consolidate board def. 2010-10-29 19:06:53 +09:00
rtc-ds1305.c RTC: Convert rtc drivers to use the alarm_irq_enable method 2011-02-03 13:02:35 -08:00
rtc-ds1307.c RTC: Convert rtc drivers to use the alarm_irq_enable method 2011-02-03 13:02:35 -08:00
rtc-ds1374.c rtc: convert DS1374 to dev_pm_ops 2011-03-22 17:44:16 -07:00
rtc-ds1390.c spi/rtc-{ds1390,ds3234,m41t94}: Use spi_get_drvdata() for SPI devices 2011-03-17 10:32:47 -06:00
rtc-ds1511.c drivers/rtc/rtc-ds1511.c: world-writable sysfs nvram file 2011-03-22 17:44:16 -07:00
rtc-ds1553.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-ds1672.c
rtc-ds1742.c sysfs: add struct file* to bin_attr callbacks 2010-05-21 09:37:31 -07:00
rtc-ds3232.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-ds3234.c spi/rtc-{ds1390,ds3234,m41t94}: Use spi_get_drvdata() for SPI devices 2011-03-17 10:32:47 -06:00
rtc-efi.c rtc: add platform driver for EFI 2009-04-01 08:59:24 -07:00
rtc-em3027.c rtc: add EM3027 rtc driver 2011-05-26 17:12:33 -07:00
rtc-ep93xx.c rtc: ep93xx: Initialize drvdata before registering device 2011-05-06 17:42:04 -07:00
rtc-fm3130.c rtc: fixes and new functionality for fm3130 2010-08-11 08:59:07 -07:00
rtc-generic.c parisc: rtc: Rename rtc-parisc to rtc-generic 2009-04-02 01:05:31 +00:00
rtc-imxdi.c rtc: driver for the DryIce block found in i.MX25 chips 2010-08-11 08:59:07 -07:00
rtc-isl1208.c drivers/rtc/rtc-isl1208.c: add alarm support 2011-03-22 17:44:16 -07:00
rtc-isl12022.c rtc-isl12022: properly handle military hour format 2010-08-11 08:59:08 -07:00
rtc-jz4740.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-lib.c RTC: Rework RTC code to use timerqueue for events 2010-12-10 22:24:24 -08:00
rtc-lpc32xx.c Fix common misspellings 2011-03-31 11:26:23 -03:00
rtc-m41t80.c rtc: m41t80: Initialize clientdata before registering device 2011-05-06 18:01:02 -07:00
rtc-m41t93.c spi/rtc-m41t93: Use spi_get_drvdata() for SPI devices 2011-06-08 14:33:48 -06:00
rtc-m41t94.c spi/rtc-{ds1390,ds3234,m41t94}: Use spi_get_drvdata() for SPI devices 2011-03-17 10:32:47 -06:00
rtc-m48t35.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
rtc-m48t59.c RTC: Convert rtc drivers to use the alarm_irq_enable method 2011-02-03 13:02:35 -08:00
rtc-m48t86.c rtc/m48t86: use rtc_valid_tm() to check returned tm 2010-08-11 08:59:07 -07:00
rtc-max6900.c rtc/max6900: use rtc_valid_tm() to check returning tm 2010-08-11 08:59:07 -07:00
rtc-max6902.c rtc: rtc-max6902 - set driver data in max6902_probe() 2011-01-13 08:03:12 -08:00
rtc-max8925.c rtc: max8925: Initialize drvdata before registering device 2011-05-06 18:02:00 -07:00
rtc-max8998.c rtc: max8998: Initialize drvdata before registering device 2011-05-06 18:02:02 -07:00
rtc-mc13xxx.c rtc: mc13xxx: Don't call rtc_device_register while holding lock 2011-05-06 18:02:07 -07:00
rtc-mpc5121.c Merge branch 'devicetree/next' of git://git.secretlab.ca/git/linux-2.6 2011-03-16 17:28:10 -07:00
rtc-mrst.c drivers/rtc/rtc-mrst.c: use release_mem_region after request_mem_region 2011-05-26 17:12:33 -07:00
rtc-msm6242.c rtc: msm6242: Initialize drvdata before registering device 2011-05-06 18:02:03 -07:00
rtc-mv.c RTC: Convert rtc drivers to use the alarm_irq_enable method 2011-02-03 13:02:35 -08:00
rtc-mxc.c drivers/rtc/rtc-mxc.c: remove defines already included in rtc.h 2011-05-26 17:12:33 -07:00
rtc-nuc900.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-omap.c RTC: rtc-omap: Fix a leak of the IRQ during init failure 2011-04-18 10:39:38 +02:00
rtc-pcap.c rtc: pcap: Initialize drvdata before registering device 2011-05-06 18:02:04 -07:00
rtc-pcf2123.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
rtc-pcf8563.c drivers/rtc/rtc-pcf8563.c: remove unused struct 2010-08-11 08:59:06 -07:00
rtc-pcf8583.c rtc: fix driver data issues in several rtc drivers 2009-12-16 07:19:58 -08:00
rtc-pcf50633.c drivers/rtc/rtc-pcf50633.c: don't request update IRQ 2011-05-26 17:12:33 -07:00
rtc-pl030.c Merge branches 'defcfg', 'drivers' and 'cyberpro-next' of master.kernel.org:/home/rmk/linux-2.6-arm 2011-03-17 18:48:35 -07:00
rtc-pl031.c Merge branches 'defcfg', 'drivers' and 'cyberpro-next' of master.kernel.org:/home/rmk/linux-2.6-arm 2011-03-17 18:48:35 -07:00
rtc-proc.c RTC: Include information about UIE and PIE in RTC driver proc. 2011-03-09 11:25:04 -08:00
rtc-ps3.c powerpc/ps3: Add rtc-ps3 2009-04-02 01:05:32 +00:00
rtc-puv3.c unicore32: move rtc-puv3.c to drivers/rtc directory 2011-06-09 16:15:24 +08:00
rtc-pxa.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-r9701.c spi: prefix modalias with "spi:" 2009-09-23 07:39:43 -07:00
rtc-rp5c01.c rtc: rp5c01: Initialize drvdata before registering device 2011-05-06 18:02:05 -07:00
rtc-rs5c313.c rtc: rtc-rs5c313: ctrl_in/outX to __raw_read/writeX conversion. 2010-10-27 15:30:32 +09:00
rtc-rs5c348.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
rtc-rs5c372.c RTC: Clean out UIE icotl implementations 2011-03-09 11:24:54 -08:00
rtc-rv3029c2.c rtc: add rv3029c2 RTC support 2011-05-26 17:12:33 -07:00
rtc-rx8025.c RTC: Cleanup rtc_class_ops->irq_set_state 2011-03-09 11:23:34 -08:00
rtc-rx8581.c drivers/rtc/rtc-rx8581.c: fix setdatetime 2010-07-27 14:32:06 -07:00
rtc-s3c.c drivers/rtc/rtc-s3c.c: fixup wake support for rtc 2011-05-11 18:50:44 -07:00
rtc-s35390a.c i2c: Remove all i2c_set_clientdata(client, NULL) in drivers 2010-06-03 11:33:58 +02:00
rtc-sa1100.c RTC: sa1100: Update the sa1100 RTC driver. 2011-03-09 11:25:08 -08:00
rtc-sh.c drivers: Final irq namespace conversion 2011-03-29 14:48:19 +02:00
rtc-spear.c rtc: add support for spear rtc 2011-05-26 17:12:33 -07:00
rtc-starfire.c
rtc-stk17ta8.c sysfs: add struct file* to bin_attr callbacks 2010-05-21 09:37:31 -07:00
rtc-stmp3xxx.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-sun4v.c
rtc-sysfs.c rtc/hctosys: only claim the RTC provided the system time if it did 2010-03-12 15:52:28 -08:00
rtc-tegra.c rtc: add real-time clock driver for NVIDIA Tegra 2011-03-22 17:44:16 -07:00
rtc-test.c RTC: Fix the cross interrupt issue on rtc-test. 2011-03-09 11:25:07 -08:00
rtc-tile.c tile: add an RTC driver for the Tilera hypervisor 2011-05-17 14:44:36 -04:00
rtc-twl.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-tx4939.c sysfs: add struct file* to bin_attr callbacks 2010-05-21 09:37:31 -07:00
rtc-v3020.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
rtc-vr41xx.c RTC: Cleanup rtc_class_ops->irq_set_freq() 2011-03-09 11:23:35 -08:00
rtc-vt8500.c rtc: add support for the RTC in VIA VT8500 and compatibles 2011-05-26 17:12:33 -07:00
rtc-wm831x.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-wm8350.c RTC: Cleanup rtc_class_ops->update_irq_enable() 2011-03-09 11:23:37 -08:00
rtc-x1205.c Fix common misspellings 2011-03-31 11:26:23 -03:00