Re: all class init functions for all types in QEMU are called in select_machine(). Expected?

[Claudio Fontana <cfontana@suse.de>]

On 3/12/21 11:39 AM, Paolo Bonzini wrote:
> On 12/03/21 11:25, Claudio Fontana wrote:
>> We can register them from there if needed I think,, but where ever we
>> do it, we still have to point to the one set of ops or the other,
>> depending on the cpu model that is finally chosen.
>>
>> So when we attach the tcg cpu accelerator object to the cpu, we
>> currently should check which cpu it is, and behave accordingly.
>>
>> Maybe this is better? Ie, not set the tcg ops in different places (in
>> the v7m cpu class init and in the tcg cpu accel init),
>>
>> but rather set them just in a single place, when we attach the accel
>> cpu object, checking which cpu profile it is somehow (TBD), and then
>> behave accordingly?
> 
> Take a look at 
> https://wiki.qemu.org/User:Paolo_Bonzini/Machine_init_sequence#Basic_phases. 
>   The phases are:
> 
> - creating backends (PHASE_NO_MACHINE)
> 
> - creating machine (after which PHASE_MACHINE_CREATED is entered)
> 
> - creating accelerator (after which PHASE_ACCEL_CREATED is entered)
> 
> - initializing embedded devices (in machine_run_board_init, after which 
> PHASE_MACHINE_INITIALIZED is entered), including CPUs
> 
> - creating devices (in qmp_x_exit_preconfig, after which 
> PHASE_MACHINE_READY is entered)
> 
> And the last is where the guest actually starts.
> 
> I think that you should have a callback in the accelerator that runs 
> after -cpu is processed and before PHASE_MACHINE_INITIALIZED is entered. 
>   So the right place to add it would be machine_run_board_init.
> 
> Maybe some kind of double dispatch, where the accelerator has an 
> acc->init_cpu(acc, cc) method and the CPU has a cc->init_tcg_ops(cc) 
> method.  Then TCG's init_cpu calls into the latter.
> 
> Paolo
> 
> 

Thanks, digesting this.

What you describe as:

acc->init_cpu(acc, cc)

seems to me we already have, as the accel class init, fe, for x86/tcg:

static void tcg_cpu_accel_class_init(ObjectClass *oc, void *data)
{
    AccelCPUClass *acc = ACCEL_CPU_CLASS(oc);

#ifndef CONFIG_USER_ONLY
    acc->cpu_realizefn = tcg_cpu_realizefn;
#endif /* CONFIG_USER_ONLY */

    acc->cpu_class_init = tcg_cpu_class_init;
    acc->cpu_instance_init = tcg_cpu_instance_init;
}

acc->cpu_class_init() call would then be the acc->init_cpu call you mention.

The only thing we seem to be missing is the cc->init_tcg_ops(cc)..

Ciao,

Claudio