Re: [PATCH v2] clocksource: exynos-mct: Register the timer for stable udelay

Will Deacon
2014-06-20T08:15:57Z

On Thu, Jun 19, 2014 at 05:40:49PM +0100, Tomasz Figa wrote:
> On 19.06.2014 18:31, Doug Anderson wrote:
> >>> My personal vote would be to submit a patch to change "cycles_t" to
> >>> always be 32-bits. Given that 32-bits was fine for udelay() for ARM
> >>> that seems sane and simple. If someone later comes up with a super
> >>> compelling reason why we need 64-bit timers for udelay (really??) then
> >>> they can later add all the complexity needed.
> >>
> >> Yes, this could work. I'm not sure what else cycles_t is used for, though.
> >
> > True, it is a bit questionable to change this since it's a type that's
> > not obviously just for udelay(). Perhaps a better option would be to
> > make a new typedef for the result of read_current_timer(). ...or just
> > change it to return a u32?
> >
>
> Sounds good to me, but let's hear other opinions. I'm adding Will and
> Jonathan as they wrote the ARM delay timer code.

I think cycles_t is only used for small interval calculations at the moment,
but I remember Ted mentioning something about using it (or something
similar) as a source of early entropy, in which case the more bits the
better.

That said, I can't find any code in the tree to that effect.

Will