On NTP, RTCs and accurately setting their time

[Russell King - ARM Linux]

On Wed, Sep 20, 2017 at 04:45:22PM -0600, Jason Gunthorpe wrote:
> What do you think of this untested approach in the below patch?

There's another issue.

Most drivers use rtc_device_register() or devm_rtc_device_register()
rather than rtc_allocate_device() (which is static.)  This does not
give RTC drivers a chance to set rtc->time_set_nsec before the
RTC is registered with the kernel.

Setting it after the device has been registered is racy.  So, having
this member in struct rtc_device and assuming that drivers will override
the value doesn't work.

It doesn't make sense to put it in rtc_class_ops as it isn't an
operation, but we could add a callback in there which is used during
initialisation but before registration which could be used to set this
member.

Thoughts?

-- 
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