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authorJason Gunthorpe <jgunthorpe@obsidianresearch.com>2017-10-13 11:54:33 -0600
committerJohn Stultz <john.stultz@linaro.org>2017-10-30 15:03:24 -0700
commit0f295b0650c90362b4111f46d7f9149a0a4191be (patch)
tree4589b6e58d710ac1f2967317305c6c8fc28903d3 /drivers/rtc/class.c
parent9e66317d3c92ddaab330c125dfe9d06eee268aff (diff)
downloadlinux-0f295b0650c90362b4111f46d7f9149a0a4191be.tar.bz2
rtc: Allow rtc drivers to specify the tv_nsec value for ntp
ntp is currently hardwired to try and call the rtc set when wall clock tv_nsec is 0.5 seconds. This historical behaviour works well with certain PC RTCs, but is not universal to all rtc hardware. Change how this works by introducing the driver specific concept of set_offset_nsec, the delay between current wall clock time and the target time to set (with a 0 tv_nsecs). For x86-style CMOS set_offset_nsec should be -0.5 s which causes the last second to be written 0.5 s after it has started. For compat with the old rtc_set_ntp_time, the value is defaulted to + 0.5 s, which causes the next second to be written 0.5s before it starts, as things were before this patch. Testing shows many non-x86 RTCs would like set_offset_nsec ~= 0, so ultimately each RTC driver should set the set_offset_nsec according to its needs, and non x86 architectures should stop using update_persistent_clock64 in order to access this feature. Future patches will revise the drivers as needed. Since CMOS and RTC now have very different handling they are split into two dedicated code paths, sharing the support code, and ifdefs are replaced with IS_ENABLED. Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Miroslav Lichvar <mlichvar@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Stephen Boyd <stephen.boyd@linaro.org> Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com> Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'drivers/rtc/class.c')
-rw-r--r--drivers/rtc/class.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 2ed970d61da1..722d683e0b0f 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -161,6 +161,9 @@ static struct rtc_device *rtc_allocate_device(void)
device_initialize(&rtc->dev);
+ /* Drivers can revise this default after allocating the device. */
+ rtc->set_offset_nsec = NSEC_PER_SEC / 2;
+
rtc->irq_freq = 1;
rtc->max_user_freq = 64;
rtc->dev.class = rtc_class;