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authorThomas Gleixner <tglx@linutronix.de>2020-12-06 22:46:17 +0100
committerThomas Gleixner <tglx@linutronix.de>2020-12-11 10:40:52 +0100
commit354c796b9270eb4780e59e3bdb83a3ae4930a832 (patch)
tree38f8f7774340d4bd208d7f00fd02a89fe9d8137a
parentb0ecd8e8c5ef376777277c4c2db7de92ac59f23f (diff)
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
-rw-r--r--drivers/rtc/class.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 7c88d190c51f..d7957376eb96 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;