[PATCH 1/2] ARM: s3c64xx: cpuidle: convert to platform driver

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

On 10/25/2013 10:52 PM, Tomasz Figa wrote:
> On Friday 25 of October 2013 21:13:35 Daniel Lezcano wrote:
>> On 10/25/2013 12:39 PM, Tomasz Figa wrote:
>>> Hi Daniel,
>>>
>>> [Sending again, without HTML part. Sorry for the noise.]
>>>
>>> On Friday 25 of October 2013 09:11:13 Daniel Lezcano wrote:
>>>> The driver is tied with the pm low level code making difficult to
>>>> split
>>>> the driver into a more arch independent code. The platform driver
>>>> allows
>>>> to move the standby callback into the platform data field and use a
>>>> simple driver with no more dependency on the low level code.
>>>>
>>>> The standby callback has a portion of code to set the standby method
>>>> and
>>>> the effective cpu_do_idle switching the cpu to the right mode. As this
>>>> code is redundant in the cpu suspend code, it has been factored out
>>>> when
>>>> implementing the standby methdod.
>>>>
>>>> By this way, the driver is ready to be moved out to the
>>>> drivers/cpuidle.
>>>
>>> The idea itself is quite good, but unfortunately I have to NAK this.
>>> Please see details in comments below.
>>>
>>>> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
>>>> ---
>>>>
>>>>    arch/arm/mach-s3c64xx/cpuidle.c |   38
>>>>
>>>> ++++++++++++++++---------------------- arch/arm/mach-s3c64xx/pm.c
>>>> |
>>>>
>>>>     33 ++++++++++++++++++++++++++------- 2 files changed, 42
>>>>
>>>> insertions(+), 29 deletions(-)
>>
>> [ ... ]
>>
>>>> -
>>>> -	tmp = __raw_readl(S3C64XX_PWR_CFG);
>>>> -	tmp &= ~S3C64XX_PWRCFG_CFG_WFI_MASK;
>>>> -	tmp |= S3C64XX_PWRCFG_CFG_WFI_SLEEP;
>>>
>>> Finally note the S3C64XX_PWRCFG_CFG_WFI_SLEEP flag here again.
>>
>> Ouch ! I missed it. Thanks for spotting the problem.
>>
>>> I believe it should be visible now what's wrong with this patch. To
>>> make
>>> sure it is, let me explain how the system controller of S3C64xx handles
>>> WFI requests.
>>>
>>> When the CPU issues WFI request to the syscon, it takes an action
>>> depending on how it is configured. A bit field is there in one of
>>> syscon registers (S3C64XX_PWR_CFG) that selects what action to perform
>>> in case of WFI request.
>>>
>>> You can program the syscon to ignore the request, enter IDLE mode,
>>> enter
>>> STOP mode or enter SLEEP mode. As the names suggest, for cpuidle, it
>>> needs to be programmed for IDLE mode and for system-wide sleep it
>>> needs to be set to SLEEP mode. STOP mode is not very useful as it has
>>> mostly the same effect that can be achieved by performing fine-grained
>>> clock and power gating of peripherals manually, so it is unused by
>>> Linux.
>>
>> Yes, this is what I assumed but I missed the CFG_WFI_SLEEP flag, my eyes
>> read CFG_WFI_IDLE.
>>
>>> Now, my take on the issue you are trying to solve would be a bit
>>> different. Since the S3C64xx does not have any interesting cpuidle
>>> modes, just a normal, clock-gated WFI mode, it does not need to have a
>>> cpuidle driver at all. All that is needed is simply setting up the
>>> S3C64XX_PWRCFG_CFG_WFI field to S3C64XX_PWRCFG_CFG_WFI_IDLE early at
>>> boot-up, then set it to S3C64XX_PWRCFG_CFG_WFI_SLEEP just before
>>> entering the sleep mode and restore it back to
>>> S3C64XX_PWRCFG_CFG_WFI_IDLE after waking up.
>> So you are suggesting to remove the cpuidle driver ?
>
> Exactly.

I see.

>> Won't it be worth to add a new WFI_SLEEP state to the cpuidle driver ?
>
> I don't think so. How a suspend-to-RAM specific thing like WFI_SLEEP could
> be relevant to a cpuidle driver? (Unless there are some plans to
> consolidate STR with cpuidle that I haven't heard about...)

I finally found a documentation for the s3c6410x and the description of 
the different modes. Indeed, the sleep mode is not adequate for a 
cpuidle state. What about the 'stop' and 'deep stop' state ?

What is 'STR' ?

Thanks
   -- Daniel




-- 
  <http://www.linaro.org/> Linaro.org ? Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog