[PATCH v4 5/5] arm: exynos: Add MCPM call-back functions

Abhilash Kesavan kesavan.abhilash at gmail.com
Mon May 5 09:26:38 PDT 2014

Hi Andrew,

On Fri, May 2, 2014 at 11:53 PM, Andrew Bresticker
<abrestic at chromium.org> wrote:
>>> +     /*
>>> +      * TODO: Turn off the clusters when all cores in the cluster
>>> +      * are down to achieve significant power savings.
>>> +      */
>> This comment should actually be located right after the
>> "if (exynos_cluster_unused(cluster))" above.  That is where the cluster
>> control should be applied, assuming it'll be effective only when WFI is
>> executed.
> Correct me if I'm wrong Samsung folks, but I thought it was not
> possible to apply cluster power control from a CPU within the cluster
> being powered down, i.e. a CPU in the other cluster must be the one to
> apply the cluster power control to power down the outbound cluster.
I was under the same impression until quite recently. However, based
on inputs from the hardware team, there are bits available (in the
*COMMON_OPTION register) that ensure "ARM_CORE0~3 are turned off
earlier and then ARM_COMMON_L2 is turned off finally". This allows us
to turn off the cluster from a cpu of the same cluster. We have used
these bits in our cluster power down cpuidle state implementation as

> -Andrew

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