Re: [Qemu-devel] [PATCH 6/6] arm: drop intermadiate cpu_model -> cpu type parsing and use cpu type directly

[Igor Mammedov <imammedo@redhat.com>]

On Sat, 9 Sep 2017 17:30:14 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Tue, Sep 05, 2017 at 03:46:07PM -0700, Alistair Francis wrote:
> > On Tue, Sep 5, 2017 at 3:12 PM, Eduardo Habkost <ehabkost@redhat.com> wrote:  
> > > On Tue, Sep 05, 2017 at 02:47:52PM -0700, Alistair Francis wrote:  
> > >> On Tue, Sep 5, 2017 at 2:31 PM, Eduardo Habkost <ehabkost@redhat.com> wrote:  
> > > [...]  
> > >> >> diff --git a/hw/arm/stm32f205_soc.c b/hw/arm/stm32f205_soc.c
> > >> >> index f61e735..1cd6374 100644
> > >> >> --- a/hw/arm/stm32f205_soc.c
> > >> >> +++ b/hw/arm/stm32f205_soc.c
> > >> >> @@ -112,7 +112,7 @@ static void stm32f205_soc_realize(DeviceState *dev_soc, Error **errp)
> > >> >>
> > >> >>      armv7m = DEVICE(&s->armv7m);
> > >> >>      qdev_prop_set_uint32(armv7m, "num-irq", 96);
> > >> >> -    qdev_prop_set_string(armv7m, "cpu-model", s->cpu_model);
> > >> >> +    qdev_prop_set_string(armv7m, "cpu-type", s->cpu_type);
> > >> >>      object_property_set_link(OBJECT(&s->armv7m), OBJECT(get_system_memory()),
> > >> >>                                       "memory", &error_abort);
> > >> >>      object_property_set_bool(OBJECT(&s->armv7m), true, "realized", &err);
> > >> >> @@ -200,7 +200,7 @@ static void stm32f205_soc_realize(DeviceState *dev_soc, Error **errp)
> > >> >>  }
> > >> >>
> > >> >>  static Property stm32f205_soc_properties[] = {
> > >> >> -    DEFINE_PROP_STRING("cpu-model", STM32F205State, cpu_model),
> > >> >> +    DEFINE_PROP_STRING("cpu-type", STM32F205State, cpu_type),  
> > >> >
> > >> > Same as armv7m: are we 100% sure users are not setting this
> > >> > manually?  
> > >>
> > >> In an embedded board like this it really doesn't make sense to let the
> > >> user overwrite the CPU. The SoC will take it as an option, but the
> > >> board (which creates the SoC) just blindly always uses the same CPU.
> > >> That feature is more for QOMificatoion then any real reason though.
> > >>  
> > >
> > > I'm not talking about -cpu (no user-visible change in the
> > > handling of -cpu should result from this patch), but about
> > > possible cases where the user set the "cpu-model" property using
> > > another mechanism, like -global.  Probably it's impossible for an
> > > user to override the property successfully, but I would like to
> > > be sure.  
> > 
> > Ah, that is trickier.
> > 
> > I guess that is possible to do, but the object setting logic should
> > handle the error gracefully and inform the user of the error.  
> 
> After looking at the code more closely, I think we can be 100%
> sure the user doesn't rely on the property, because:
> 
> * TYPE_ARMV7M and TYPE_STM32F205_SOC are both sysbus devices
>   with user_creatable=false, so the user can't instantiate them
>   directly;
> * The only places where those objects are realized inside the
>   code are:
>   * mps2_common_init()
>   * netduino2_init()
>   * stm32f205_soc_realize()
>   * armv7m_init()
>   Those functions always set the "cpu-model" property immediately
>   before realize.
> 
> This means any value set by the user (e.g. using -global) would
> be always overwritten before realize.
> 
> However, I have a suggestion for Igor: making a separate patch
> that renames the existing property to "x-cpu-model", and using
> "x-cpu-type" in this series.  This way we will explicitly
> document the fact that the property is not a stable
> user/management interface.
There is no much point in renaming to "x-cpu-model" as it will be deleted
right afterwards, I'd just delete "cpu-model" and use "x-cpu-type"
in this patch. I'm not a fun of 'x-' prefix and would prefer a flag
in property to mark it as internal. But it's out of scope of this series,
so I don't care much about naming at the moment and will use "x-cpu-type"
as you suggest.

> 
> >   
> > >
> > >  
> > >> In saying that I think a warning if the user tries to set the CPU
> > >> would make sense. I know that this issues comes up in other ARM boards
> > >> (Zynq-7000 has the same issue as well) so maybe a machine property
> > >> saying that the board doesn't accept custom CPUs would be a good idea.  
> > >
> > > Yeah, there are multiple cases in this patch where boards are
> > > validating the CPU model, but not all boards do that.  A generic
> > > MachineClass::valid_cpu_types[] field would be useful.
> > >  
> > >>
> > >> Overall I think this patch is moving in the right direction though and
> > >> this CPU option being ignored existed before this series.  
> > >
> > > I agree this is going on the right direction.  However, I don't
> > > see any board that ignore the CPU option: all of them seem to use
> > > cpu_model when creating the CPUs, already.  
> > 
> > The Netduino2 will ignore any CPU options and always use a Cortex-m3.
> > I was wrong about Zynq-7000 though, it does respect the -cpu option.
> > 
> > Thanks,
> > Alistair
> >   
> > >
> > > --
> > > Eduardo  
>