Re: [PATCH v2] clocksource/arm_arch_timer: Fix masking for high freq counters

[Oliver Upton]

On Sun, Aug 8, 2021 at 3:40 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> On Sun, 08 Aug 2021 02:14:35 +0100,
> Oliver Upton <oupton@xxxxxxxxxx> wrote:
>
> > The only other sane idea that I could come up with is providing this
> > information to the kernel through DT, although that would leave ACPI
> > systems behind.
>
> It also has the disadvantage that a large number of DT timer nodes are
> a mess of cargo-culted, copy-pasted idioms, and that adding another
> property would only make it worse.

Agreed, this does seem like the best solution, short of the
architecture actually providing something to determine the counter
width.

On that note, I wonder how (if ever) we will be able to move away from
unnecessarily masking a 64 bit counter, i.e. a v8.6 or above
implementation. With this patch, one such counter would wrap after
36.56 years, short of the 40 year guarantee we have from the
architecture for < v8.6 implementations. Getting it to 64 bits would
squarely make it someone else's problem ~585 years from now :)

--
Thanks,
Oliver