Re: [Qemu-devel] [PATCH] rtc: introduce nmi disable bit handler for cmos

[Paolo Bonzini]

On 16/12/2015 11:28, Gonglei (Arei) wrote:
> I'll move the global nmi_disabled into RTCState, then I have to add a global 
> RTCState
> Variable so that other C files can use the rtc_state->external_nmi_disabled.

Hmm, I think it should be done differently.  This is a layering
violation, the NMI_EN is essentially a pin (qemu_irq) between the ISA
bridges and the RTC.  The NMI "button" is also a component of the ISA
bridge; you should not need to touch anything except the RTC and the ISA
bridges, in particular not the APICs.

First, you need to add a qemu_irq argument to rtc_init. The RTC can
raise/lower the IRQ on writes to port 0x70.

Second, make the ISA bridges implement NMIState, where the
implementation of NMIState is similar to inject_nmi in hw/core/nmi.c:

    CPU_FOREACH(cs) {
        X86CPU *cpu = X86_CPU(cs);

        if (!cpu->apic_state) {
            cpu_interrupt(cs, CPU_INTERRUPT_NMI);
        } else {
            apic_deliver_nmi(cpu->apic_state);
        }
    }

Third, the ISA bridges (hw/isa/piix4.c and hw/isa/lpc_ich9.c) need to
export a qemu_irq for nmi_en IRQ (e.g. using qdev_init_gpio_in_named),
and you should modify the ISA bridge's implementation of NMIState to
latch the NMI if you send one while NMIs are disabled.  The nmi_en IRQ
can also trigger an NMI when nmi_en is enabled and an NMI was latched.
The nmi_en status and NMI latch status must be migrated in a new
subsection of the ISA bridges.

Fourth, the PC machines should use qdev_get_gpio_in_named to retrieve
the qemu_irq from the ISA bridges, and pass it to pc_basic_device_init.

I may have messed up some steps, but this is the basic idea.

Paolo