From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Miroslav Lichvar <mlichvar@redhat.com>,
John Stultz <john.stultz@linaro.org>,
Prarit Bhargava <prarit@redhat.com>,
Alessandro Zummo <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>
Subject: [patch 3/8] rtc: cmos: Make rtc_cmos sync offset correct
Date: Sun, 06 Dec 2020 22:46:16 +0100 [thread overview]
Message-ID: <20201206220541.830517160@linutronix.de> (raw)
In-Reply-To: 20201206214613.444124194@linutronix.de
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))
next prev parent reply other threads:[~2020-12-06 22:08 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-06 21:46 [patch 0/8] ntp/rtc: Fixes and cleanups Thomas Gleixner
2020-12-06 21:46 ` [patch 1/8] rtc: mc146818: Prevent reading garbage Thomas Gleixner
2021-01-25 18:40 ` [patch 1/8] rtc: mc146818: Prevent reading garbage - bug Mickaël Salaün
2021-01-26 13:26 ` Thomas Gleixner
2021-01-26 14:17 ` Mickaël Salaün
2021-01-26 15:35 ` Thomas Gleixner
2021-01-26 17:02 ` [PATCH V2] rtc: mc146818: Detect and handle broken RTCs Thomas Gleixner
2021-01-26 18:00 ` Alexandre Belloni
2021-01-31 10:59 ` Dirk Gouders
2021-02-01 13:53 ` Serge Belyshev
2021-02-01 19:09 ` [PATCH] rtc: mc146818: Dont test for bit 0-5 in Register D Thomas Gleixner
2021-02-01 19:24 ` [PATCH V2] " Thomas Gleixner
2021-02-01 19:32 ` Linus Torvalds
2021-02-01 19:40 ` Thomas Gleixner
2021-02-11 23:09 ` Maciej W. Rozycki
2021-02-01 19:38 ` Alexandre Belloni
2021-02-01 20:09 ` Borislav Petkov
2021-02-01 20:15 ` Dirk Gouders
2021-02-02 4:22 ` Len Brown
2021-02-03 13:00 ` Mickaël Salaün
2020-12-06 21:46 ` [patch 2/8] rtc: mc146818: Reduce spinlock section in mc146818_set_time() Thomas Gleixner
2020-12-06 21:46 ` Thomas Gleixner [this message]
2020-12-07 20:50 ` [patch 3/8] rtc: cmos: Make rtc_cmos sync offset correct Jason Gunthorpe
2020-12-06 21:46 ` [patch 4/8] rtc: core: Make the sync offset default more realistic Thomas Gleixner
2020-12-07 20:55 ` Jason Gunthorpe
2020-12-10 23:59 ` Alexandre Belloni
2020-12-11 0:23 ` Thomas Gleixner
2020-12-11 0:28 ` Alexandre Belloni
2020-12-06 21:46 ` [patch 5/8] ntp: Make the RTC synchronization more reliable Thomas Gleixner
2020-12-07 12:47 ` Miroslav Lichvar
2020-12-07 20:59 ` Jason Gunthorpe
2020-12-29 19:41 ` Geert Uytterhoeven
2021-01-11 10:12 ` Thomas Gleixner
2021-01-11 10:40 ` Geert Uytterhoeven
2020-12-06 21:46 ` [patch 6/8] ntp, rtc: Move rtc_set_ntp_time() to ntp code Thomas Gleixner
2020-12-07 20:59 ` Jason Gunthorpe
2020-12-09 3:51 ` Alexandre Belloni
2020-12-06 21:46 ` [patch 7/8] ntp: Make the RTC sync offset less obscure Thomas Gleixner
2020-12-06 21:46 ` [patch 8/8] ntp: Consolidate the RTC update implementation Thomas Gleixner
2020-12-07 21:05 ` Jason Gunthorpe
2020-12-11 9:23 ` Thomas Gleixner
2020-12-09 0:33 ` [patch 0/8] ntp/rtc: Fixes and cleanups Thomas Gleixner
2020-12-09 4:01 ` Alexandre Belloni
2020-12-09 12:39 ` Thomas Gleixner
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