The following commit has been merged into the timers/core branch of tip:
Commit-ID: b0ecd8e8c5ef376777277c4c2db7de92ac59f23f
Gitweb:
https://git.kernel.org/tip/b0ecd8e8c5ef376777277c4c2db7de92ac59f23f
Author: Thomas Gleixner <[email protected]>
AuthorDate: Sun, 06 Dec 2020 22:46:16 +01:00
Committer: Thomas Gleixner <[email protected]>
CommitterDate: Fri, 11 Dec 2020 10:40:52 +01:00
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 <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Acked-by: Alexandre Belloni <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
drivers/rtc/rtc-cmos.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index c633319..7728fac 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))
