Messages in this thread Patch in this message | | | Date | Sun, 06 Dec 2020 22:46:16 +0100 | From | Thomas Gleixner <> | Subject | [patch 3/8] rtc: cmos: Make rtc_cmos sync offset correct |
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The offset for rtc_cmos must be -500ms to work correctly with the current implementation of rtc_set_ntp_time() due to the following:
tsched twrite(t2.tv_sec - 1) t2 (seconds increment)
twrite - tsched is the transport time for the write to hit the device, which is negligible for this chip because it's accessed directly.
t2 - twrite = 500ms according to the datasheet.
But rtc_set_ntp_time() calculation of tsched is:
tsched = t2 - 1sec - (t2 - twrite)
The default for the sync offset is 500ms which means that the write happens at t2 - 1.5 seconds which is obviously off by a second for this device.
Make the offset -500ms so it works correct.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- drivers/rtc/rtc-cmos.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/drivers/rtc/rtc-cmos.c +++ b/drivers/rtc/rtc-cmos.c @@ -868,6 +868,9 @@ cmos_do_probe(struct device *dev, struct if (retval) goto cleanup2; + /* Set the sync offset for the periodic 11min update correct */ + cmos_rtc.rtc->set_offset_nsec = -(NSEC_PER_SEC / 2); + /* export at least the first block of NVRAM */ nvmem_cfg.size = address_space - NVRAM_OFFSET; if (rtc_nvmem_register(cmos_rtc.rtc, &nvmem_cfg))
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