[PATCH] hw/ppc: fix decrementer with BookE timers

[PATCH] hw/ppc: fix decrementer with BookE timers

[Clément Chigot]

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.

Signed-off-by: Clément Chigot <chigot@adacore.com>
Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
---
 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;
-- 
2.25.1

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Clément Chigot]

Hi,

Gentle ping + CC missing maintainers.

Thanks Clément

On Mon, Jul 15, 2024 at 10:46 AM Clément Chigot <chigot@adacore.com> 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.
>
> Signed-off-by: Clément Chigot <chigot@adacore.com>
> Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
> ---
>  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;
> --
> 2.25.1
>

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Clément Chigot]

Hey,

Gentle ping

Thanks Clément

On Mon, Jul 29, 2024 at 10:33 AM Clément Chigot <chigot@adacore.com> wrote:
>
> Hi,
>
> Gentle ping + CC missing maintainers.
>
> Thanks Clément
>
> On Mon, Jul 15, 2024 at 10:46 AM Clément Chigot <chigot@adacore.com> 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.
> >
> > Signed-off-by: Clément Chigot <chigot@adacore.com>
> > Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
> > ---
> >  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;
> > --
> > 2.25.1
> >

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Philippe Mathieu-Daudé]

Adding Cédric

On 27/8/24 13:49, Clément Chigot wrote:
> Hey,
> 
> Gentle ping
> 
> Thanks Clément
> 
> On Mon, Jul 29, 2024 at 10:33 AM Clément Chigot <chigot@adacore.com> wrote:
>>
>> Hi,
>>
>> Gentle ping + CC missing maintainers.
>>
>> Thanks Clément
>>
>> On Mon, Jul 15, 2024 at 10:46 AM Clément Chigot <chigot@adacore.com> 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.
>>>
>>> Signed-off-by: Clément Chigot <chigot@adacore.com>
>>> Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
>>> ---
>>>   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;
>>> --
>>> 2.25.1
>>>
> 

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Cédric Le Goater]

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.

> Signed-off-by: Clément Chigot <chigot@adacore.com>
> Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")

LGTM,

Reviewed-by: Cédric Le Goater <clg@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,

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;

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Clément Chigot]

On Tue, Aug 27, 2024 at 7:40 PM Cédric Le Goater <clg@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 <chigot@adacore.com>
> > Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
>
> LGTM,
>
> Reviewed-by: Cédric Le Goater <clg@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;
>
>

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Cédric Le Goater]

On 8/28/24 09:21, Clément Chigot wrote:
> On Tue, Aug 27, 2024 at 7:40 PM Cédric Le Goater <clg@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 <chigot@adacore.com>
>>> Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
>>
>> LGTM,
>>
>> Reviewed-by: Cédric Le Goater <clg@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

Nice. Do you have any plans to upstream the machine ?

Thanks,

C.

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Clément Chigot]

On Thu, Aug 29, 2024 at 2:33 PM Cédric Le Goater <clg@kaod.org> wrote:
>
> On 8/28/24 09:21, Clément Chigot wrote:
> > On Tue, Aug 27, 2024 at 7:40 PM Cédric Le Goater <clg@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 <chigot@adacore.com>
> >>> Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
> >>
> >> LGTM,
> >>
> >> Reviewed-by: Cédric Le Goater <clg@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
>
> Nice. Do you have any plans to upstream the machine ?

That was the plan. However, we are using that emulation in order to
test VxWorks on PPC.  Recent versions have now officially provided a
BSP for QEmu using ppce500 board. We are planning to transition to it,
mainly to avoid having to maintain that P3041DS home-made
implementation. Thus, I'm not sure we'll spend time on upstreaming it
:(
That being said, if you heard people being interested in that board,
please do warn me.

Thanks,
Clément

> Thanks,
>
> C.
>

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Clément Chigot]

Hi Cédric,

On Tue, Aug 27, 2024 at 7:40 PM Cédric Le Goater <clg@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.
>
> > Signed-off-by: Clément Chigot <chigot@adacore.com>
> > Fixed: 8e0a5ac87800 ("hw/ppc: Avoid decrementer rounding errors")
>
> LGTM,
>
> Reviewed-by: Cédric Le Goater <clg@redhat.com>

Unless I'm wrong this patch has not been queued yet. Is there any
reason for this ?
I just want to make sure it hasn't been forgotten.

Thanks,
Clément

> We have some automated tests with the ppce500 machine which it would be
> interesting  to extend to have a better coverage of booke.
>
> Thanks,
>
> 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;
>
>

Re: [PATCH] hw/ppc: fix decrementer with BookE timers

[Cédric Le Goater]

Hello Clément,

> Unless I'm wrong this patch has not been queued yet. Is there any
> reason for this ?

I don't think there was a PPC PR yet. We are just starting the
QEMU 9.2 cycle [*]. Since this is a fix that applies on older
releases, may be we could have a PR in not too long.

Thanks,

C.

[*] https://wiki.qemu.org/Planning/9.2