[Qemu-devel] Re: [PATCH 0/6] Make hpet a compile time option

[Juan Quintela]

Paul Brook <address@hidden> wrote:
>> On 05/24/2010 11:32 AM, Paul Brook wrote:
>> >> Notice that this patch was sent against hpet as one example, if we agree
>> >> that this "way" of disabling devices is ok, we could disable more
>> >> devices/have more flexibility.  Notice that in general, we (RHEL/KVM)
>> >> are interested in a small subset of qemu devices.
>> > 
>> > IMO this patch is a backwards step.  The device models should be cleaned
>> > up so that you don't need to make a compile time decision.
>> 
>> I disagree.  I think the device model should be cleaned up so that no
>> CONFIG_HPET is required in code but I think it's still useful to be able
>> to exclude device models from the build.  That should just be a matter
>> of not building the object though (that's the point of device_init()).
>
> I think we're saying the same thing.
>
> We already have a mechanism for avoiding things at build time - specifically 
> config-devices.mak. We don't have a nice UI for it, but it's there.
> At worst your distro specific patch is a 1-line change to default-
> configs/i386-softmmu.mak.
>
> I have no objection to moving hpet.c into Makefile.objs, conditional on 
> CONFIG_HPET (like e.g. CONFIG_SERIAL/serial.o).  However a necessary 
> prerequisite is that you fix the device model and machine initialisation so 
> that it's possible to omit hpet.o without rebuilding anything else.

We have two exported functions:

void hpet_init(qemu_irq *irq);
uint32_t hpet_in_legacy_mode(void);

This is how one is used in mc14818rtc:

#if defined TARGET_I386
    if (!hpet_in_legacy_mode())
#endif

how the other one is used on pc.c

    if (!no_hpet) {
        hpet_init(isa_irq);
    }

I agree that I could probably came with some trick with qdev_create() to
substitute the hpet_init() (my understanding is that jan already have it
or something like that).

But for the other call, what do you propose?

My best try was to hide the availability of hpet inside hpet_emul.h
with:

#ifdef CONFIG_HPET
uint32_t hpet_in_legacy_mode(void);
else
uint32_t hpet_in_legacy_mode(void) { return 0;}
#endif

I can't see any obvious way to change the hpet_in_legacy_mode() that is
cleaner than this.

Thanks, Juan.

> Paul