Re: [PATCH v22 03/11] clocksource: arm_arch_timer: refactor arch_timer_needs_probing

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On Wed, Mar 29, 2017 at 04:24:08PM +0100, Mark Rutland wrote:
> On Tue, Mar 28, 2017 at 05:02:20PM +0200, Daniel Lezcano wrote:
> > On Wed, Mar 22, 2017 at 12:31:14AM +0800, fu.wei@linaro.org wrote:
> > > From: Fu Wei <fu.wei@linaro.org>
> > > 
> > > When system init with device-tree, we don't know which node will be
> > > initialized first. And the code in arch_timer_common_init should wait
> > > until per-cpu timer and MMIO timer are both initialized. So we need
> > > arch_timer_needs_probing to detect the init status of system.
> > > 
> > > But currently the code is dispersed in arch_timer_needs_probing and
> > > arch_timer_common_init. And the function name doesn't specify that
> > > it's only for device-tree. This is somewhat confusing.
> > 
> > Can the following patch help you to solve nicely the situation ?
> > 
> > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1360007.html
> 
> This does not help.
> 
> The needs_probing logic is all there to bodge around a problem with
> registering sched_clock, when you have two sources of the same
> frequency, but one is otherwise better.
> 
> The sysreg clocksource has much lower latency than the MMIO clocksource,
> so we always want to use that as the sched_clock if we have it.
> Currently, the code ensures this by deferring registration of
> sched_clock.
> 
> Ideally, we'd figure that out dynamically, or we'd have a rating
> argument.
> 

Ok, I see. Thanks.

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