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authorThomas Gleixner <tglx@linutronix.de>2020-12-06 22:46:16 +0100
committerThomas Gleixner <tglx@linutronix.de>2020-12-11 10:40:52 +0100
commitb0ecd8e8c5ef376777277c4c2db7de92ac59f23f (patch)
treed068dfd5fd0975a676891ea8be5c71d5a88e0c7e /drivers/rtc/rtc-cmos.c
parentrtc: mc146818: Reduce spinlock section in mc146818_set_time() (diff)
downloadlinux-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.c3
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))