Re: [PATCH v3 3/3] cpuidle: big.LITTLE: vexpress-TC2 CPU idle driver

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

On 08/08/2013 06:18 PM, Lorenzo Pieralisi wrote:
> On Thu, Aug 08, 2013 at 05:00:24PM +0100, Daniel Lezcano wrote:
>> On 08/07/2013 01:43 PM, Lorenzo Pieralisi wrote:
>>> The big.LITTLE architecture is composed of two clusters of cpus. One cluster
>>> contains less powerful but more energy efficient processors and the other
>>> cluster groups the powerful but energy-intensive cpus.
>>>
>>> The TC2 testchip implements two clusters of CPUs (A7 and A15 clusters in
>>> a big.LITTLE configuration) connected through a CCI interconnect that manages
>>> coherency of their respective L2 caches and intercluster distributed
>>> virtual memory messages (DVM).
>>>
>>> TC2 testchip integrates a power controller that manages cores resets, wake-up
>>> IRQs and cluster low-power states. Power states are managed at cluster
>>> level, which means that voltage is removed from a cluster iff all cores
>>> in a cluster are in a wfi state. Single cores can enter a reset state
>>> which is identical to wfi in terms of power consumption but simplifies the
>>> way cluster states are entered.
>>>
>>> This patch provides a multiple driver CPU idle implementation for TC2
>>> which paves the way for a generic big.LITTLE idle driver for all
>>> upcoming big.LITTLE based systems on chip.
>>>
>>> The driver relies on the MCPM infrastructure to coordinate and manage
>>> core power states; in particular MCPM allows to suspend specific cores
>>> and hides the CPUs coordination required to shut-down clusters of CPUs.
>>>
>>> Power down sequences for the respective clusters are implemented in the
>>> MCPM TC2 backend, with all code needed to clean caches and exit coherency.
>>>
>>> The multiple driver CPU idle infrastructure allows to define different
>>> C-states for big and little cores, determined at boot by checking the
>>> part id of the possible CPUs and initializing the respective logical
>>> masks in the big and little drivers.
>>>
>>> Current big.little systems are composed of A7 and A15 clusters, as
>>> implemented in TC2, but in the future that may change and the driver
>>> will have evolve to retrieve what is a 'big' cpu and what is a 'little'
>>> cpu in order to build the correct topology.
>>>
>>> Cc: Kevin Hilman <khilman@linaro.org>
>>> Cc: Amit Kucheria <amit.kucheria@linaro.org>
>>> Cc: Olof Johansson <olof@lixom.net>
>>> Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
>>> Cc: Rafael J. Wysocki <rjw@sisk.pl>
>>> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
>>> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>>> ---
>>
>> A nit below :/
>>
>> [ ... ]
>>
>>> +
>>> +static struct cpuidle_driver bl_idle_big_driver = {
>>> +	.name = "big_idle",
>>> +	.owner = THIS_MODULE,
>>> +	.states[0] = ARM_CPUIDLE_WFI_STATE,
>>> +	.states[1] = {
>>> +		.enter			= bl_enter_powerdown,
>>> +
>>> +		.exit_latency		= 500,
>>
>> Extra line between enter and exit_latency.
> 
> Gah, not anymore :)
> 
> Other than that, is it ready to go ? If nobody complains I have planned
> to send a pull request early next week, as soon as a stable branch for
> TC2 MCPM gets in arm-soc.


It sounds good to me.




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