[PATCH] arch_timer: Move delay timer to drivers clocksource

Daniel Lezcano daniel.lezcano at linaro.org
Mon Jan 20 10:28:03 EST 2014

On 01/20/2014 03:56 PM, Lorenzo Pieralisi wrote:
> On Mon, Jan 20, 2014 at 02:42:10PM +0000, Daniel Lezcano wrote:
>> On 01/17/2014 07:36 PM, Stephen Boyd wrote:
>>> On 01/17/14 05:40, Prashant Gaikwad wrote:
>>>> Another requirement:
>>>> We have 3 timers T1, T2, T3 used as wake events for 3 idle states C1,
>>>> C2, C3 respectively.
>>>> Rating of T2 is better than T3. If I register T2 and T3 both as
>>>> broadcast timers then T3 will not be used. But ...
>>>>       - T2 is not preserved in C3 idle state.
>>>>       - T3 resolution is very poor (ms) and can not be used as wake
>>>> event for C2.
>>>> Possible solution, register only T3 as broadcast device and use T2 as
>>>> per-CPU fallback timer.
>>> We have the same situation on MSM. I've been thinking about proposing we
>>> allow multiple broadcast timers to exist in the system and then have the
>>> clockevents_notify() caller indicate which C state is being entered. The
>>> broadcast timers would need to indicate which C state they don't work in
>>> though.
>> IMO, there are different solutions:
>> 1. extend the C3STOP to C1STOP, C2STOP, etc ... and pass the idle state
>> to the time framework where these flags are checked against. I don't
>> like this approach but it is feasible.
>> 2. use the generic power domain. When the power domain is shutdown via
>> the cpuidle backend driver, it switches the timer.
> IMO, 2 is the way forward. It is the only solution that links resources to
> the reason they need maintainance (ie power management). I am writing
> v2 of C-state proposal where power domains are explicitly associated with
> devices (eg arch timers), and 2 fits well with this approach.

Thanks Lorenzo for your feedback.

   -- Daniel

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