Re: [Qemu-devel] [qemu-s390x] [PATCH v3 5/9] s390x/tcg: properly implement the TOD

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 26 Jun 2018 14:06:00 +0200
David Hildenbrand <david@redhat.com> wrote:

> >> @@ -34,10 +58,24 @@ static void qemu_s390_tod_class_init(ObjectClass *oc, void *data)
> >>      tdc->set = qemu_s390_tod_set;
> >>  }
> >>  
> >> +static void qemu_s390_tod_init(Object *obj)
> >> +{
> >> +    S390TODState *td = S390_TOD(obj);
> >> +    struct tm tm;
> >> +
> >> +    qemu_get_timedate(&tm, 0);
> >> +    td->base.high = 0;
> >> +    td->base.low = TOD_UNIX_EPOCH + (time2tod(mktimegm(&tm)) * 1000000000ULL);
> >> +    if (td->base.low < TOD_UNIX_EPOCH) {
> >> +        td->base.high += 1;
> >> +    }
> >> +}  
> > 
> > Nit: It would be sufficient to do this in the realize() function instead.  
> 
> Then I'll have to overwrite the realize function and store the
> parent_realize function - something that I want to avoid if not really
> necessary.

Agreed. I'd just leave it as it is now.

> 
> (for now it was also done in the cpu initfn, so that should be fine)
> 
> >   
> >>  static TypeInfo qemu_s390_tod_info = {
> >>      .name = TYPE_QEMU_S390_TOD,
> >>      .parent = TYPE_S390_TOD,
> >>      .instance_size = sizeof(S390TODState),
> >> +    .instance_init = qemu_s390_tod_init,
> >>      .class_init = qemu_s390_tod_class_init,
> >>      .class_size = sizeof(S390TODClass),
> >>  };  
> > [...]  
> >> diff --git a/target/s390x/misc_helper.c b/target/s390x/misc_helper.c
> >> index dd5273949b..be341b5295 100644
> >> --- a/target/s390x/misc_helper.c
> >> +++ b/target/s390x/misc_helper.c
> >> @@ -28,6 +28,8 @@
> >>  #include "qemu/timer.h"
> >>  #include "exec/exec-all.h"
> >>  #include "exec/cpu_ldst.h"
> >> +#include "qapi/error.h"
> >> +#include "tcg_s390x.h"
> >>  
> >>  #if !defined(CONFIG_USER_ONLY)
> >>  #include "sysemu/cpus.h"
> >> @@ -39,6 +41,7 @@
> >>  #include "hw/s390x/ioinst.h"
> >>  #include "hw/s390x/s390-pci-inst.h"
> >>  #include "hw/boards.h"
> >> +#include "hw/s390x/tod.h"
> >>  #endif
> >>  
> >>  /* #define DEBUG_HELPER */
> >> @@ -138,25 +141,32 @@ void HELPER(spx)(CPUS390XState *env, uint64_t a1)
> >>  /* Store Clock */
> >>  uint64_t HELPER(stck)(CPUS390XState *env)
> >>  {
> >> -    uint64_t time;
> >> +    S390TODState *td = s390_get_todstate();
> >> +    S390TODClass *tdc = S390_TOD_GET_CLASS(td);
> >> +    S390TOD tod;
> >>  
> >> -    time = env->tod_offset +
> >> -        time2tod(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL));
> >> -
> >> -    return time;
> >> +    tdc->get(td, &tod, &error_abort);
> >> +    return tod.low;
> >>  }
> >>  
> >>  /* Set Clock Comparator */
> >>  void HELPER(sckc)(CPUS390XState *env, uint64_t time)
> >>  {
> >> +    S390TODState *td = s390_get_todstate();
> >> +    S390TODClass *tdc = S390_TOD_GET_CLASS(td);
> >> +    S390TOD tod_base;
> >> +
> >>      if (time == -1ULL) {
> >>          return;
> >>      }
> >>  
> >>      env->ckc = time;
> >>  
> >> +    tdc->get(td, &tod_base, &error_abort);
> >> +    tod_base.low -= time2tod(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL));  
> > 
> > So the tdc->get first adds the time2tod, and then you subtract it here
> > again? Can't you simply use td->base.low directly instead?  
> 
> That might be a good idea, previously I had tdc->get_base(), but dropped
> it because it cannot be implemented for KVM.
> 
> Simply accessing the member here should be fine. Thanks!

So, we're guaranteed to have td->base.low at the correct value? (Sorry,
having a bit of a hard time following around here.)

> 
> >   
> >>      /* difference between origins */
> >> -    time -= env->tod_offset;
> >> +    time -= tod_base.low;
> >>  
> >>      /* nanoseconds */
> >>      time = tod2time(time);
> >> @@ -164,6 +174,14 @@ void HELPER(sckc)(CPUS390XState *env, uint64_t time)
> >>      timer_mod(env->tod_timer, time);
> >>  }  
> > 
> > ... I found only nits, so with or without my suggested modifications:
> > 
> > Reviewed-by: Thomas Huth <thuth@redhat.com>
> >   
> 
>