[PATCH] clocksource: arm_global_timer: Allow DT to specify already reset timer counter

[daniel.lezcano@linaro.org (Daniel Lezcano)]

On 12/17/2015 10:37 AM, Jassi Brar wrote:
> On 16 December 2015 at 12:29, Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>> On 12/16/2015 05:11 AM, Jassi Brar wrote:
>>>
>>> On Tue, Dec 15, 2015 at 11:32 PM, Daniel Lezcano
>>> <daniel.lezcano@linaro.org> wrote:
>>>>
>>>> On 11/25/2015 06:24 AM, Jassi Brar wrote:
>>>>>
>>>>>
>>>>> The GT counter is common to every core in a cluster. There is a usecase
>>>>> when Linux is spawned by a 'master' firmware/OS running on some core of
>>>>> the same cluster and the GT is used by the both.
>>>>>     Linux, upon boot, resetting the GT counter is obviously fatal to the
>>>>> other OS. So provide a way for DT to tell Linux if it's running in that
>>>>> 'slave' mode and must not reset the counter.
>>>>>
>>>>> Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
>>>>
>>>>
>>>>
>>>> Hmm, I doubt that is a hardware description.
>>>>
>>> Its a regular 2core-1cluster platform. The master RTOS on cpu0
>>> maintains the lifecycle of Linux on cpu1.
>>>
>>> 'No_Counter_Reset' is not a h/w thing, I agree, but I don't know how
>>> to better convey that platform specific constraint.
>>
>>
>> May be with a kernel parameter ?
>>
> The fact, that arch-timer driver does it via DT (see commit
> 65b5732d241b8), changes anything? :)

It is debatable (cc'ed Rob).

I acked it because the patch was on the edge between soft/hw in the 
description. But now it sounds like that created a precedence and we 
consider these DT options exceptions as acceptable.

I don't know if there is a better way than a kernel parameter but IMO it 
makes sense to pass this kind of options via the kernel command line as 
we can extend it easily for more options in the future.

Furthermore, I suspect this feature may be needed for other arch/plat. 
So having a generic option could be useful for future changes.

Thomas, do you have an opinion ?

Can we consider adding a set of kernel parameters instead of adding DT 
exceptions time to time ?

eg.

clocksource.reset = <0/1>
clocksource.virtual = <0/1>



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