RTC: Remove the logic to update time format when DM bit changed

Changing the DM (binary/BCD) and 24/12 control bit doesn't affect the internal
registers. It only indicates what format is used for those registers.

Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
RTC: Rename rtc_timer_update

Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
RTC: introduce RTC_CLOCK_RATE

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
RTC: Update interrupt state when interrupts are masked/unmasked

If an interrupt flag is already set when the interrupt becomes enabled,
raise an interrupt immediately, and vice versa if interrupts become
disabled.

Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
vmstate: add VMSTATE_TIMER_V

Also, for consistency with other occurrences, implement VMSTATE_TIMER
as a special case of VMSTATE_TIMER_V rather than VMSTATE_TIMER_TEST.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
RTC: Update the RTC clock only when reading it

Calculate guest RTC based on the time of the last update, instead of
using timers.  The formula is

    (base_rtc + guest_time_now - guest_time_last_update + offset)

Base_rtc is the RTC value when the RTC was last updated.
Guest_time_now is the guest time when the access happens.
Guest_time_last_update was the guest time when the RTC was last updated.
Offset is used when divider reset happens or the set bit is toggled.

The timer is kept in order to signal interrupts, but it only needs to
run when either UF or AF is cleared.  When the bits are both set, the
timer does not run.

UIP is now synthesized when reading register A.  If the timer is not set,
or if there is more than one second before it (as is the case at the
end of this series), the leading edge of UIP is computed and the rising
edge occurs 220us later.  If the update timer occurs within one second,
however, the rising edge of the AF and UF bits should coincide withe
the falling edge of UIP.  We do not know exactly when this will happen
because there could be delays in the servicing of the timer.  Hence, in
this case reading register A only computes for the rising edge of UIP,
and latches the bit until the timer is fired and clears it.

Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
RTC: Add divider reset support

The first update cycle begins one-half seconds after divider
reset is removed.  This feature is useful for testing.

Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
RTC: Do not fire timer periodically to catch next alarm

This patch limits further the usage of a periodic timer.  It computes the
time of the next alarm, and uses it to skip all intermediate occurrences
of the timer.

Cc: Yang Zhang <yang.z.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
RTC: Get and set time without going through s->current_tm

This patch makes rtc_set_time and rtc_set_cmos work without reading
s->current_tm.  In the case of rtc_set_time I introduce a new
function that retrieves the time and stores into a given struct tm
(not hard-coded to s->current_tm).  In the case of rtc_set_cmos, the
current time is similarly taken from a struct tm rather than
s->current_tm.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
RTC: Remove the current_tm field

This is not used anymore and only written to.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
wb

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>