Re: [External] Re: [PATCH v3] arm64: topology: add source check in arch_cpu_idle_enter()

[Xuewen Yan]

On Thu, Aug 27, 2026 at 5:02 PM Beata Michalska <beata.michalska@xxxxxxx> wrote:
>
> On Mon, Aug 24, 2026 at 05:21:03PM +0800, Xuewen Yan wrote:
> > On Thu, Aug 20, 2026 at 3:11 AM Beata Michalska <beata.michalska@xxxxxxx> wrote:
> > >
> > Should we distinguish between events?
> We could although for this particular issue clearing the source is the one that
> needs attention. But I do not see why we could not have both.
> This was just sharing the idea, not a final patch.
> >
> > > ---
> > >
> > > This is just a rough idea, and needs ironing out the wrinkles, which are there,
> > > but that allows leaving the idle enter as is. I also believe this is the right
> > > approach for the interface itself, although I also see some drawbacks and
> > > potential issues (in its current state), especially that the functionality is
> > > being exposed to modules.
> > > Nevertheless, those are my two cents, untested, just sketched.
> >
> > As an aside, could we verify the functionality of the AMU's
> > SYS_AMEVCNTR0_CONST_EL0 in the current CPU before enabling amu_file?
> > To my knowledge, many chips currently have inaccurate errata in this counter.
> > Alternatively, could we introduce a command line that allows users to
> > dynamically disable this feature?
> >
> > Thanks!
> Do you have any particular issue in mind ?
> So far, from what I have been able to track, the issues reported are either
> handled by existing erratum or by the latest change that reads the counters in
> 'one go'. Can you share the details of the issue you are facing ?
> That would be helpful in potentially finding the right solution.

For example:
There is an A725 errata:
[A725]The CNT_CYCLES event can have a significant increment error due to WFE/WFI
Status
Fault type: Programmer Category B
Fault status: Present in r0p0, r0p1, and r0p2. Open.
......
Workaround
There is no workaround.

Thanks!
>
> ---
> BR
> Beata
>