The PL031 RTC provides two features: a real-time counter and an alarm
interrupt. To use the alarm, the driver normally writes a time value
into the match register RTCMR, and when the counter reaches that value
the device triggers the interrupt.
At the moment the implementation ignores programming of the alarm, as
the feature seems rarely used in VMs. However the interrupt is still
triggered arbitrarily when the guest writes to registers, and the line
is never cleared. This really confuses the Linux driver, which loops in
the interrupt handler until Linux realizes that no one is dealing with
the interrupt (200000 unanswered calls) and disables the handler.
One way to fix this would be implementing the alarm function properly,
which isn't too difficult but requires adding some async timer logic
which probably won't ever get used. In addition the device's interrupt
is level-triggered and we don't support level interrupts at the moment,
though we could probably get away with changing this interrupt to edge.
The simplest fix, though, is to just disable the interrupt logic
entirely, so that the alarm function still doesn't work but the guest
doesn't see spurious interrupts.
Add a default() implementation to satisfy clippy's new_without_default
check, since Rtc::new() doesn't take a parameter after this change.
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
4528e2f1ea