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| author | Thomas Gleixner <tglx@linutronix.de> | 2020-12-06 22:46:16 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-12-11 10:40:52 +0100 |
| commit | b0ecd8e8c5ef376777277c4c2db7de92ac59f23f (patch) | |
| tree | d068dfd5fd0975a676891ea8be5c71d5a88e0c7e /drivers/rtc/rtc-cmos.c | |
| parent | rtc: mc146818: Reduce spinlock section in mc146818_set_time() (diff) | |
| download | linux-b0ecd8e8c5ef376777277c4c2db7de92ac59f23f.tar.xz linux-b0ecd8e8c5ef376777277c4c2db7de92ac59f23f.zip | |
rtc: cmos: Make rtc_cmos sync offset correct
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>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201206220541.830517160@linutronix.de
Diffstat (limited to 'drivers/rtc/rtc-cmos.c')
| -rw-r--r-- | drivers/rtc/rtc-cmos.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c index c633319cdb91..7728faca01b4 100644 --- a/drivers/rtc/rtc-cmos.c +++ b/drivers/rtc/rtc-cmos.c @@ -868,6 +868,9 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq) 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)) |