Re: [PATCH] arm: omap2: Kconfig: select TWD and global timer on AM43xx devices

[santosh shilimkar <santosh.shilimkar@oracle.com>]

On 11/18/2015 6:33 AM, Grygorii Strashko wrote:
> On 11/13/2015 06:39 PM, santosh shilimkar wrote:
>> On 11/13/2015 5:07 AM, Mason wrote:
>>> On 13/11/2015 13:48, Grygorii Strashko wrote:
>>>> On 11/12/2015 08:06 PM, Felipe Balbi wrote:
>>>>> Make sure to tell the kernel that AM437x has
>>>>> TWD and global timers.
>>>>>
>>>>> Signed-off-by: Felipe Balbi <balbi@ti.com>
>>>>> ---
>>>>>
>>>>> Hi Tony,
>>>>>
>>>>> now that all dependencies are in place, we can
>>>>> finally enable twd and global_timer for AM437x.
>>>>>
>> Is AM437x SMP SOC ?
>
> No. But it has ARM TWD and GT
>
>> Is TWD on AM437x works in low power states ?
>
> No. But TWD, seems, is not a problem here if omap gp timer
> can be used as broadcast device.
>
>> Probably I haven't followed the recent updates, but does
>> the TWD supports C3STOP on UP systems ? The broadcast
>> code was SMP only in past, and TWD use to die in
>> low power state on past OMAP SOCs.
>>
>> If either of these are still the issue then
>> TWD shouldn't be used.
>>
>
> Yep. I see the problem with ARM Global timer here if
> CPUIdle is enabled and ARM Global timer is selected as
> clocksource device.
>
Its expected and well known limitation.

> I think, it will be right thing to disable "global_timer"
> and "local_timer" nodes in am437x.dtsi by default - if
> someone would like to use them then those nodes have
> to be enabled explicitly in board file.
> (TWD timer will be enabled on OMAP multi SoC build
>   irrespectively of HAVE_ARM_TWD is selected for am437x or not,
>   because it will be selected for omap4).
> I've just sent corresponding patch:
>   http://www.spinics.net/lists/arm-kernel/msg461141.html
>
> Also, probably, it could be reasonable to:
> - make ARM_GLOBAL_TIMER fully selectable option and allow select it from defconfig.
>
> - or - update this patch as below
> -       select ARM_GLOBAL_TIMER
> -       select CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
> +       select ARM_GLOBAL_TIMER if !CPU_IDLE
> +       select CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK if ARM_GLOBAL_TIMER
>
>
+1