On Tue, Aug 27, 2024 at 7:40 PM Cédric Le Goater <c...@kaod.org> wrote:
>
> Hello Clément,
>
> On 7/15/24 10:46, Clément Chigot wrote:
> > The BookE decrementer stops at 0, meaning that it won't decremented
> > towards "negative" values.
> > However, the current logic is inverted: decr is updated solely when
> > the resulting value would be negative.
>
> How did you hit the issue ? which machine ? I didn't see any error
> when booting Linux 6.6.3 on mpc8544ds, e500mc, e5500 and e6500.
I hit this issue while running some version of VxWorks on a custom
machine: p3041ds (description [1] and our local implementation [2]).
So, I'm not that surprised you were not able to reproduce.
> > Signed-off-by: Clément Chigot <chi...@adacore.com>
> > Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
>
> LGTM,
>
> Reviewed-by: Cédric Le Goater <c...@redhat.com>
>
> We have some automated tests with the ppce500 machine which it would be
> interesting to extend to have a better coverage of booke.
Thanks for the pointer, I'll see if I can extend them.
> Thanks,
>
> C.
>
[1]
https://www.nxp.com/design/design-center/software/qoriq-developer-resources/p3041-qoriq-development-system:P3041DS
[2] https://github.com/AdaCore/qemu/blob/qemu-stable-9.0.0/hw/ppc/p3041ds.c
>
> > ---
> > hw/ppc/ppc.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
> > index e6fa5580c0..9fc85c7de0 100644
> > --- a/hw/ppc/ppc.c
> > +++ b/hw/ppc/ppc.c
> > @@ -729,7 +729,9 @@ static inline int64_t __cpu_ppc_load_decr(CPUPPCState
> > *env, int64_t now,
> > int64_t decr;
> >
> > n = ns_to_tb(tb_env->decr_freq, now);
> > - if (next > n && tb_env->flags & PPC_TIMER_BOOKE) {
> > +
> > + /* BookE timers stop when reaching 0. */
> > + if (next < n && tb_env->flags & PPC_TIMER_BOOKE) {
> > decr = 0;
> > } else {
> > decr = next - n;
>
>
