Re: [RFC patch 02/11] cpuidle / arm : a single cpuidle driver

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

On 03/25/2013 07:27 PM, Catalin Marinas wrote:
> On 15 March 2013 15:07, Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>> On 03/15/2013 03:47 PM, Arnd Bergmann wrote:
>>> On Friday 15 March 2013, Daniel Lezcano wrote:
>>>> The cpuidle drivers are duplicating a lot of code and in most
>>>> of the case there is a common pattern we can factor out:
>>>>
>>>>         * setup the broadcast timers
>>>>         * register the driver
>>>>         * register the devices
>>>>
>>>> This arm driver is the common part between all the ARM cpuidle drivers,
>>>> with the code factored out.
>>>>
>>>> It does not handle the coupled idle state for now but it is the first
>>>> step to have everyone to converge to the same code pattern.
>>>>
>>>> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
>>>
>>> Unfortunately, I missed the session in Hong Kong, but I'd like to understand
>>> what part of this driver is actually ARM specific. I assume there is nothing
>>> in it that depends on 32 bit ARM hardware, right?
>>
>> What depends on the 32bits ARM hardware is the drivers themselves. This
>> ARM driver is the first step to consolidate all SoC cpuidle specific
>> code we find in arch/arm. The code is designated to factor out these
>> drivers, as a first step. The second step is to consolidate more this
>> driver (eg. moving the code in arch/arm/kernel/cpuidle.c in this driver).
>>
>> The last man standing algorithm we have in mach-ux500 and mach-imx is
>> the same, and will be moved in the ARM cpuidle driver.
>>
>> The more it will be consolidated, the more it will be ARM specific.
>>
>> The final step will be to use the device tree to be passed to this
>> driver and do the cpuidle driver initialization from there.
>>
>>> Would the same code be used with arch/arm64?
>>
>> I can't tell but IIUC, a single ARM driver will be used based on the
>> psci for ARM64, but it does not exist for now. It is possible some code
>> pattern could be used from the ARM32 cpuidle driver.
> 
> While we recommend PSCI if EL3 (secure mode) is available, not all
> ARMv8 CPU implementations will have this and most likely we'll have to
> reuse existing cpuidle drivers. So if you can make it as generic as
> possible it would really help.

Sure, I will keep it in mind.

Thanks for the information.

 -- Daniel


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