Re: [PATCH] ARM: EXYNOS: mcpm: Don't rely on firmware's secondary_cpu_start

[Chander Kashyap]

On Wed, Jun 11, 2014 at 3:43 PM, Lorenzo Pieralisi
<lorenzo.pieralisi@xxxxxxx> wrote:
> On Wed, Jun 11, 2014 at 05:52:10AM +0100, Chander Kashyap wrote:
>> Hi Doug,
>>
>> On Tue, Jun 10, 2014 at 9:19 PM, Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> wrote:
>> > On Tue, 10 Jun 2014, Doug Anderson wrote:
>> >
>> >> My S-state knowledge is not strong, but I believe that Lorenzo's
>> >> questions matter if we're using S2 for CPUidle (where we actually turn
>> >> off power and hot unplug CPUs) but not when we're using S1 for CPUidle
>> >> (where we just enter WFI/WFE).
>> >>
>>
>> No Its not plain WFI.
>>
>> All cores in Exynos5420 can be powered off independently.
>> This functionality has been tested.
>>
>> Below is the link for the posted patches.
>>
>> https://lkml.org/lkml/2014/6/10/194
>>
>> And as Nicolas wrote, these patches need MCPM for that.
>
> Chander, I cast a look into the code and I have a question
> (you also told me on CPUidle review that only core off
> is supported in CPUidle).
>
> When you say all cores can be powered off independently, do
> you also mean that clusters can be powered off (in CPUidle) ?
>
> I am pointing this out since in the MCPM backend I noticed:
>
> "/* TODO: Turn off the cluster here to save power. */"
>
> I do not see any cluster power down request in the down path.
>
> If I am wrong, ignore my message, I am just writing to help.
>
> If you can only power down cores, but not the clusters on idle,
> please keep in mind that you are currently cleaning and invalidating
> the L2 when last man is running and this must not be taken
> lightly since, if L2 stays on, that's a massive energy waste
> for nothing.
>
> So, if clusters stay up, you _have_ to tweak the MCPM backend slightly
> to avoid cleaning L2, that's pivotal.

Hi Lorenzo,
Cluster shutdown is in progress. Abhilash will add support for that.

https://www.mail-archive.com/linux-samsung-soc@xxxxxxxxxxxxxxx/msg31104.html


>
> Lorenzo
>
>>
>> >> I believe that in ChromeOS we use S1 CPUidle and that it works fine.
>> >> We've never implemented S2 that I'm aware of.
>> >
>> > You'll have to rely on MCPM for that.  That's probably why it hasn't
>> > been implemented before.
>> >
>> >
>> > Nicolas
>> >
>> > _______________________________________________
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>> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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