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| author | Thomas Gleixner <tglx@linutronix.de> | 2020-12-06 22:46:17 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-12-11 10:40:52 +0100 |
| commit | 354c796b9270eb4780e59e3bdb83a3ae4930a832 (patch) | |
| tree | 38f8f7774340d4bd208d7f00fd02a89fe9d8137a /drivers/rtc/class.c | |
| parent | b0ecd8e8c5ef376777277c4c2db7de92ac59f23f (diff) | |
| download | linux-354c796b9270eb4780e59e3bdb83a3ae4930a832.tar.gz | |
rtc: core: Make the sync offset default more realistic
The offset which is used to steer the start of an RTC synchronization
update via rtc_set_ntp_time() is huge. The math behind this is:
tsched twrite(t2.tv_sec - 1) t2 (seconds increment)
twrite - tsched is the transport time for the write to hit the device.
t2 - twrite depends on the chip and is for most chips one second.
The rtc_set_ntp_time() calculation of tsched is:
tsched = t2 - 1sec - (t2 - twrite)
The default for the sync offset is 500ms which means that twrite - tsched
is 500ms assumed that t2 - twrite is one second.
This is 0.5 seconds off for RTCs which are directly accessible by IO writes
and probably for the majority of i2C/SPI based RTC off by an order of
magnitude. Set it to 5ms which should bring it closer to reality.
The default can be adjusted by drivers (rtc_cmos does so) and could be
adjusted further by a calibration method which is an orthogonal problem.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201206220541.960333166@linutronix.de
Diffstat (limited to 'drivers/rtc/class.c')
| -rw-r--r-- | drivers/rtc/class.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c index 7c88d190c51fc..d7957376eb96a 100644 --- a/drivers/rtc/class.c +++ b/drivers/rtc/class.c @@ -201,7 +201,7 @@ static struct rtc_device *rtc_allocate_device(void) device_initialize(&rtc->dev); /* Drivers can revise this default after allocating the device. */ - rtc->set_offset_nsec = NSEC_PER_SEC / 2; + rtc->set_offset_nsec = 5 * NSEC_PER_MSEC; rtc->irq_freq = 1; rtc->max_user_freq = 64; |