Re: [Xen-devel] [PATCH v7 16/32] xen/x86: allow disabling the pmtimer

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.10.15 at 16:36, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 30/10/15 13:16, Jan Beulich wrote:
>>>>> On 30.10.15 at 13:50, <roger.pau@xxxxxxxxxx> wrote:
>>> El 14/10/15 a les 16.37, Jan Beulich ha escrit:
>>>>>>> On 02.10.15 at 17:48, <roger.pau@xxxxxxxxxx> wrote:
>>>>> Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
>>>>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>>>>> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>>> ---
>>>>> Changes since v6:
>>>>>  - Return ENODEV in pmtimer_load if the timer is disabled.
>>>>>  - hvm_acpi_power_button and hvm_acpi_sleep_button become noops if the
>>>>>    pmtimer is disabled.
>>>> But how are those two features connected? I don't think you can
>>>> assume absence of a PM block just because there's no PM timer.
>>>> Or if you want to tie them together for now, the predicate needs
>>>> to be renamed.
>>>>
>>>>>  - Return ENODEV if pmtimer_change_ioport is called with the pmtimer
>>>>>    disabled.
>>>> Same here.
>>> What about changing XEN_X86_EMU_PMTIMER into XEN_X86_EMU_PM and this
>>> flags disables all PM stuff?
>> Ah, right, that's a reasonable option.
> 
> It still might be a nice idea to split them in two, given future work.
> 
> To support hotplug properly (cpu, ram and pci), Xen needs to inject
> GPEs, which comes from part of the PM infrastructure.  To support PCI
> devices in the future without the whole PM infrastructure, it would be
> nice to keep the split.

Coming back to this - I'm not sure: The hotplug aspect as you
mention it should matter for Dom0 only. DomU could (and perhaps
should) use a PV interface instead.

So I'd like to suggest quite the opposite: Don't call the thing PM,
but make it more general and call it ACPI. And instead of
separating HPET, we might have this fall under ACPI as well, or
we might have a second TIMER flag, requiring both to be set
for there to be a HPET and PMTMR. This leaves open the option
of Dom0 getting ACPI enabled (despite this then being "real",
not emulated ACPI), but TIMER left off.

Jan

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