On Mon, Jan 21, 2019 at 11:30 AM Pramod Kumar <[email protected]> wrote:
>
>
>
> On Mon, Jan 21, 2019 at 11:28 AM Pramod Kumar <[email protected]>
> wrote:
>>
>> Hi Sudeep,
>>
>> Thanks for having a glance on the patch. Please see my reply in line.
>>
>> Regards,
>> Pramod
>>
>> On Fri, Jan 18, 2019 at 5:02 PM Sudeep Holla <[email protected]> wrote:
>>>
>>> On Fri, Jan 18, 2019 at 11:16:20AM +0530, Pramod Kumar wrote:
>>> > If CPU hotplug is supported, ipi_cpu_stop should use PSCI cpudie
>>> > call to stop the CPU. This call ensures L1/L2 cache flush,
>>> > CPUs cache-cohenrecy setting w.r.to interconnect.
>>> >
>>>
>>> Firstly, this is not specific to PSCI and I don't see any PSCI calls as
>>> $subject claims.
>>
>>
>> I had seen all the other cpu ops methods where only PSCI supports only
>> cpu_die features hence
>> used PSCI reference in my subject line to be more clear where this die gets
>> converted in last.
>>
>>>
>>> Next, you fail to explain why do you have to ensure
>>> caches are cleaned and why do you need that in ipi_cpu_stop ?
>>> What's the use case ?
>>>
>>
>> Need comes from a specific use case where one Accelerator card(SoC) is
>> plugged in a sever over a PCIe interface. This Card gets supply from a
>> battery, which could provide very less power for a very small time, in case
>> of any power loss. Once Card switches to battery, this has to reduce its
>> power consumption to its lowest point and back-up the DDR contents asap
>> before battery gets fully drained off.
>>
>> Since battery can provide limited power for a very short time hence need to
>> transition to lowest power. As per the transition process , CPUs power
>> domain has to be off but before that it needs to flush out its content to
>> system memory(L3) so that content could be backed-up by a MCU, a controller
>> consuming very less power. Since we can not afford plugging-out every
>> individual CPUs in sequence hence uses ipi_cpu_stop for all other CPUs
>> which ultimately switch to ATF to flush out all the CPUs caches and comes
>> out of coherency domain so that its power rails could be switched-off.
>>
>>>
>>> > Apart from this, this gives control to f/w to reduce power consumption
>>> > by take appropriate decesion on power rails for plugging-out core.
>>> >
>>>
>>> May be, but ipi_cpu_stop is used is machine reboot/poweroff/halt which
>>> may restart or poweroff the system, powering down individual CPUs is not
>>> necessary and may consume lot of time in systems with large number of CPUs.
>>> It would be good to know the use-case in case I am missing to consider
>>> that.
>>
>>
>> Use case as explained above.
>>
>>>
>>> --
>>> Regards,
>>> Sudeep
