RE: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline

["Penny, Zheng" <penny.zheng@xxxxxxx>]

[Public]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Monday, May 19, 2025 9:19 PM
> To: Penny, Zheng <penny.zheng@xxxxxxx>
> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; Anthony PERARD <anthony.perard@xxxxxxxxxx>;
> Orzel, Michal <Michal.Orzel@xxxxxxx>; Julien Grall <julien@xxxxxxx>; Roger Pau
> Monné <roger.pau@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; 
> xen-
> devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen
> cmdline
>
> On 19.05.2025 10:36, Penny, Zheng wrote:
> > [Public]
> >
> >> -----Original Message-----
> >> From: Jan Beulich <jbeulich@xxxxxxxx>
> >> Sent: Tuesday, April 29, 2025 8:52 PM
> >> To: Penny, Zheng <penny.zheng@xxxxxxx>
> >> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; Andrew Cooper
> >> <andrew.cooper3@xxxxxxxxxx>; Anthony PERARD
> >> <anthony.perard@xxxxxxxxxx>; Orzel, Michal <Michal.Orzel@xxxxxxx>;
> >> Julien Grall <julien@xxxxxxx>; Roger Pau Monné
> >> <roger.pau@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> >> xen- devel@xxxxxxxxxxxxxxxxxxxx
> >> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc"
> >> xen cmdline
> >>
> >> On 14.04.2025 09:40, Penny Zheng wrote:
> >>> --- a/xen/include/acpi/cpufreq/processor_perf.h
> >>> +++ b/xen/include/acpi/cpufreq/processor_perf.h
> >>> @@ -5,6 +5,9 @@
> >>>  #include <public/sysctl.h>
> >>>  #include <xen/acpi.h>
> >>>
> >>> +/* ability bits */
> >>> +#define XEN_PROCESSOR_PM_CPPC   8
> >>
> >> This needs correlating (at least via commentary, better by build-time
> >> checking) with the other XEN_PROCESSOR_PM_* values. Otherwise
> someone
> >> adding a new #define in the public header may not (easily) notice a
> >> possible conflict. With that in mind I also question whether 8 is
> >> actually a good choice: That's the obvious next value to use in the
> >> public interface. SIF_PM_MASK is 8 bits wide, so a sensible value to use 
> >> here
> would by e.g. 0x100.
> >>
> >
> > I've added a public flag anchor "XEN_PROCESSOR_PM_PUBLIC_END" in
> public header:
> >          #define XEN_PROCESSOR_PM_PUBLIC_END
> XEN_PROCESSOR_PM_TX
> > and will do the following build-time checking:
> >         BUILD_BUG_ON(XEN_PROCESSOR_PM_CPPC <=
> > XEN_PROCESSOR_PM_PUBLIC_END);
>
> I don't really see why anything would need to be added to the public header 
> (and we
> really should strive to avoid unnecessary additions).

If I put such definition
"#define XEN_PROCESSOR_PM_PUBLIC_END XEN_PROCESSOR_PM_TX"
in internal header, I'm afraid it won't be updated if new ones added in the 
public in the future.
Or any other suggestions to provide build-time checking?

>
> Jan