Re: [chrony-dev] Re: [PATCH] test: check if RTC is RTC_UIE_ON capable

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Wed, Dec 11, 2019 at 05:42:12PM +0100, Miroslav Lichvar wrote:
> On Wed, Dec 11, 2019 at 04:13:23PM +0100, Christian Ehrhardt wrote:
> > That means the first switch_interrupts call from RTC_Initialise ->
> > RTC_Linux_Initialise -> switch_interrupts has on_off=0 and that doesn't
> > trigger the issue at initialization phase.
> > Later on on RTC_TimeInit -> switch_interrupts argument on_off=1 and the
> > issue occurs.
> > Turns out our "problematic" RTCs only trigger the issue on on_off=1.
> 
> Interesting. When I added that code I checked the kernel source code
> and it looked like enabling and disabling the interrupt should both
> return the same error.

Looking at the kernel code more carefully, it seems it checks whether
the state is changing before checking if UIE is actually supported, so
switch_interrupts(0) would fail only if interrupts were already
"enabled" (which they cannot be).

Testing both, as you did in your patch, is the correct fix.

-- 
Miroslav Lichvar


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