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

[Gonglei (Arei)]

Hello Paolo,

> 
> 
> 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

So, you mean the NMI_EN can only control NMI injection came from ISA bridge?
What's this NMI "button" mean? 

> bridge; you should not need to touch anything except the RTC and the ISA
> bridges, in particular not the APICs.
> 
Currently, the qmp command "inject-nmi" doesn't pass ISA bridge. How
do we address this situation?

> 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

We don't use hw/isa/piix4.c but hw/pci-host/piix.c in x86 target. Right?

> 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.

Sorry, I'm a bit confused. The nmi_en can trigger an NMI? Isn't a flag bit which
can enable/disable the NMI switch?

> 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

Thanks,
-Gonglei