Re: [PATCH v2 0/5] arm64: arch_timer: Improve errata handling

[Marc Zyngier <maz@kernel.org>]

On Thu, 23 Jul 2026 12:45:01 +0100,
Will Deacon <will@kernel.org> wrote:
> 
> Hi Marc,
> 
> Sorry it took me so long to look at this.

No worries, thanks for having given it a look.

[...]

> 
> I think this series is a definite improvement on the existing (broken)
> code, but there are two things that jump out at me with the new code:
> 
> 1. If somebody uses maxcpus= on perfectly working hardware, they will
>    run with the overhead of the workaround. I fear this will be
>    unpopular (and I sympathise!)... I suppose we could wait for people
>    to scream and then add something like a cmdline option to pinky
>    promise that the late CPUs are not affected by any timer errata (we
>    could presumably refuse to bring them online if they are?).

I've now added such a command-line option, forcing the counter errata
management to be disabled from boot, with a loud warning being
produced if we spot that we should have applied something.

> 
> 2. It's a bit grotty that you have to maintain your own mask to track
>    which CPUs have booted once. I'd have thought this information should
>    exist already, although none of the existing masks I could find do
>    quite what you need. One alternative would be to iterate our per-cpu
>    'cpu_data' variable or perhaps you could even use the driver's
>    existing 'arch_timer_evt' variable?

Sure, that's easy enough, just slower. Not that it should matter much.

I'll post an updated series once I've retested the various
configurations.

Thanks,

	M.

-- 
Jazz isn't dead. It just smells funny.