Re: perf usage of arch/arm64/include/asm/cputype.h

[Mark Rutland <mark.rutland@arm.com>]

On Mon, Jun 16, 2025 at 05:08:11PM +0100, Leo Yan wrote:
> On Mon, Jun 16, 2025 at 11:04:08PM +0800, Yicong Yang wrote:
> 
> [...]
> 
> > >> +static bool is_perf_midr_in_range_list(u32 midr, struct midr_range
> > >> const *ranges)
> > >> +{
> > >> +       while (ranges->model) {
> > >> +               if (midr_is_cpu_model_range(midr, ranges->model,
> > >> +                                           ranges->rv_min, ranges->rv_max)) {
> > >> +                       return true;
> > >> +               }
> > >> +               ranges++;
> > >> +       }
> > >> +       return false;
> > >> +}
> > > 
> > > Maybe we can make it more general. For example, move this function into
> > > a common header such as tools/perf/arch/arm64/include/cputype.h. Then,
> > > util/arm-spe.c can include this header.
> > > 
> > 
> > ok this sounds just like as before except rename the midr check function and modify the
> > users in perf. will do in below steps:
> > - move cpu_errata_set_target_impl()/is_midr_in_range_list() out of cputype.h
> >   since they're only used in the kernel with errata information
> > - introduce is_target_midr_in_range_list() in cputype.h to test certain MIDR
> >   is within the ranges. (is_perf_midr_in_range_list() only make sense in
> >   userspace and is a bit strange to me in a kernel header). maybe reimplement
> >   is_midr_in_range_list() with is_target_midr_in_range_list() otherwise there's
> >   no users in kernel
> > - copy cputype.h to userspace and make users use new is_target_midr_in_range_list()
> > 
> > this will avoid touching the kernel too much and userspace don't need to implement
> > a separate function.
> 
> My understanding is we don't need to touch anything in kernel side, we
> simply add a wrapper in perf tool to call midr_is_cpu_model_range().
> 
> When introduce is_target_midr_in_range_list() in kernel's cputype.h,
> if no consumers in kernel use it and only useful for perf tool, then
> it is unlikely to be accepted.

I think all of this is just working around the problem that
asm/cputype.h was never intended to be used in userspace. Likewise with
the other headers that we copy into tools/.

If there are bits that we *want* to share with tools/, let's factor that
out. The actual MIDR values are a good candidate for that -- we can
follow the same approach as with sysreg-defs.h.

Other than that, I think that userspace should just maintain its own
infrastructure, and only pull in things from kernel sources when there's
a specific reason to. Otherwise we're just creating busywork.

Mark.