Re: [PATCH V1] x86/cstate: Add Zhaoxin/Centaur ACPI Cx FFH MWAIT support

[Tony W Wang-oc]

On 23/6/2022 23:55, Dave Hansen wrote:
> On 6/22/22 18:26, Tony W Wang-oc wrote:
> > Recent Zhaoxin/Centaur CPUs support X86_FEATURE_MWAIT that implies
> > the MONITOR/MWAIT instructions can be used for ACPI Cx state.
> > The BIOS declares Cx state in _CST object to use FFH on Zhaoxin/Centaur
> > systems. So let function ffh_cstate_init() support These CPUs too.
> >
> > Signed-off-by: Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>
> > ---
> >   arch/x86/kernel/acpi/cstate.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> > index 7945eae..d4185e1 100644
> > --- a/arch/x86/kernel/acpi/cstate.c
> > +++ b/arch/x86/kernel/acpi/cstate.c
> > @@ -213,7 +213,9 @@ static int __init ffh_cstate_init(void)
> >
> >       if (c->x86_vendor != X86_VENDOR_INTEL &&
> >           c->x86_vendor != X86_VENDOR_AMD &&
> > -        c->x86_vendor != X86_VENDOR_HYGON)
> > +        c->x86_vendor != X86_VENDOR_HYGON &&
> > +        c->x86_vendor != X86_VENDOR_CENTAUR &&
> > +        c->x86_vendor != X86_VENDOR_ZHAOXIN)
> >           return -1;
>
> Many of the changelogs that add new vendors here go on about particular
> C states declared in the _CST object and contents of CPUID leaf 5.
>
> Why do we even _have_ a vendor check here?  Shouldn't the code just be
> going and doing the validation of the _CST object and CPUID that the
> changelogs blather on about?

Yes, agree!

Will change as below. Please help to check if it is OK. Thanks a lot.
 static int __init ffh_cstate_init(void)
 {
-       struct cpuinfo_x86 *c = &boot_cpu_data;
-
-       if (c->x86_vendor != X86_VENDOR_INTEL &&
-           c->x86_vendor != X86_VENDOR_AMD &&
-           c->x86_vendor != X86_VENDOR_HYGON)
+       if (!boot_cpu_has(X86_FEATURE_MWAIT))
                return -1;

> Intel certainly made the original sin on this one (see 991528d7348), but
> I hope _something_ changed in the 16 years since that patch went in.
> .

--
Sincerely
TonyWWang-oc