[PATCH 2/2] ARM: EXYNOS: add cpuidle-exynos.max_states kernel parameter

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

On 09/02/2013 03:48 PM, Bartlomiej Zolnierkiewicz wrote:
> On Monday, September 02, 2013 03:18:51 PM Daniel Lezcano wrote:
>> On 09/02/2013 11:41 AM, Bartlomiej Zolnierkiewicz wrote:
>>> On Monday, September 02, 2013 10:54:17 AM Daniel Lezcano wrote:
>>>> On 08/30/2013 12:21 PM, Bartlomiej Zolnierkiewicz wrote:
>>>>> Add "cpuidle-exynos.max_states=" parameter to allow user to specify
>>>>> the maximum of allowed CPU idle states for ARM EXYNOS cpuidle driver.
>>>>>
>>>>> This change is needed because C1 state (AFTR mode) is often not able
>>>>> to work properly due to incompatibility with some bootloader versions.
>>>>>
>>>>> Usage examples:
>>>>>
>>>>> "cpuidle-exynos.max_states=1" disables C1 state (AFTR mode).
>>>>>
>>>>> "cpuidle-exynos.max_states=0" disables the driver completely.
>>>>>
>>>>> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
>>>>> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
>>>>> Cc: Tomasz Figa <t.figa@samsung.com>
>>>>> Cc: Amit Daniel Kachhap <amit.daniel@samsung.com>
>>>>
>>>> There is a max_cstate option for acpi and intel idle. There is also the
>>>> cpuidle.off=1 option. As the semantic is the same, I think adding a
>>>> common cpuidle option usable for all the drivers is better.
>>>
>>> I thought about making the option common for all cpuidle drivers first
>>> but due to support for multiple cpuidle drivers on one machine (i.e.
>>> big.LITTLE), per-driver option looked like a better approach.
>>>
>>> Should I make the option common and not worry about multiple drivers on
>>> one machine support?
>>
>> Mmh, that's a good point.
>>
>> I am not in favor of multiple options spread across the different
>> drivers. Furthermore the max_cstate is used in the intel platform to
>> 'discover' what states the firmware supports which is not the case of
>> the cpuidle ARM drivers (except new PSCI based). This option does not
>> really fits well here.
>>
>> There is the kernel parameter 'cpuidle.off', so disabling the driver is ok.
>>
>> You converted the cpuidle driver to a platform driver. Isn't possible to
>> pass information in the platform data field at boot time to tell AFTR is
>> not supported and then act on the 'disabled' field of this state ?
> 
> It might be possible but I don't know where the source of this data would
> be, platform specific kernel parameter? It sounds just like moving the code
> around and adding superfluous platform->driver code because the similar
> kernel parameter to disable just AFTR can be added in cpuidle-exynos driver
> as well.

It is to prevent to add a new kernel parameter (with the documentation)
for a single driver which has a bogus idle state. If that could be
handled internally that would be cleaner.

Can you shortly describe what happens with the bootloader and AFTR ?

I guess you are not interested in cpuidle.off=1 because you want cpuidle
statistics for WFI, right ?




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