linux-kernel - Re: [PATCH 1/2] ARM: cpuidle: fix !cpuidle

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Date:	Wed, 30 Mar 2016 11:31:39 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] ARM: cpuidle: fix !cpuidle_ops[cpu].init case during
 init

On 03/30/2016 10:43 AM, Jisheng Zhang wrote:
> On Wed, 30 Mar 2016 10:41:09 +0200 Daniel Lezcano wrote:
>
>> On 03/30/2016 10:17 AM, Jisheng Zhang wrote:
>>> On Wed, 30 Mar 2016 10:09:12 +0200 Daniel Lezcano wrote:
>>>
>>>> On 03/30/2016 09:16 AM, Jisheng Zhang wrote:
>>>>> Hi Daniel,
>>>>
>>>> [ ... ]
>>>>
>>>> Added Lorenzo and Catalin.
>>>>
>>>>>> Hi Jisheng,
>>>>>>
>>>>>> this should be handled in the arm_cpuidle_read_ops function.
>>>>>>
>>>>>
>>>>> Thanks for reviewing. After some consideration, I think this patch isn't correct
>>>>> There may be platforms which doesn't need the init member at all, although
>>>>> currently I don't see such platforms in mainline, So I'll drop this patch
>>>>> and send out one v2 only does the optimization.
>>>>
>>>> There is an inconsistency between ARM and ARM64. The 'cpu_get_ops', the
>>>> arm_cpuidle_read_ops from the ARM64 side, returns -EOPNOTSUPP when the
>>>> init function is not there for cpuidle.
>>>
>>> yes.
>>> arm64's arm_cpuidle_init() returns -EOPNOTSUPP if init callback isn't defined
>>>
>>>>
>>>> I don't think it is a problem, but as ARM/ARM64 are sharing the same
>>>> cpuidle-arm.c driver it would make sense to unify the behavior between
>>>> both archs.
>>>
>>> yes, agree with you. From "unify" point of view, could I move back the suspend
>>> callback check and init callback check into arm_cpuidle_init() for arm as V1 does?
>>
>> Why ? To be consistent with ARM64 ?
>
> Yes, that's my intention.

Well, I don't have a strong opinion on that. ARM64 cpu_ops is slightly 
different from cpuidle_ops as the cpu boot / hotplug operations are 
placed in a different place and that explains why on ARM64 we can have 
an successful 'get_ops' because we use the partially filled structure. 
On ARM, it is cpuidle_ops only, so we can gracefully fail if the ops are 
not defined.

IMO, it still make sense to keep the checks in arm_cpuidle_read_ops for ARM.


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