Re: [PATCH v4 3/5] ARM: topology: Update cpu_power according to DT information

[Vincent Guittot <vincent.guittot@linaro.org>]

On 9 July 2012 16:37, Shilimkar, Santosh <santosh.shilimkar@ti.com> wrote:
> On Mon, Jul 9, 2012 at 8:06 PM, Vincent Guittot
> <vincent.guittot@linaro.org> wrote:
>> On 9 July 2012 15:00, Shilimkar, Santosh <santosh.shilimkar@ti.com> wrote:
>>> On Mon, Jul 9, 2012 at 6:02 PM, Vincent Guittot
>>> <vincent.guittot@linaro.org> wrote:
>>>> On 9 July 2012 12:55, Shilimkar, Santosh <santosh.shilimkar@ti.com> wrote:
>>>>> Vincent,
>>>>> On Mon, Jul 9, 2012 at 2:57 PM, Vincent Guittot
>>>>> <vincent.guittot@linaro.org> wrote:
>>>>>> Use cpu compatibility field and clock-frequency field of DT to
>>>>>> estimate the capacity of each core of the system and to update
>>>>>> the cpu_power field accordingly.
>>>>>> This patch enables to put more running tasks on big cores than
>>>>>> on LITTLE ones. But this patch doesn't ensure that long running
>>>>>> tasks will run on big cores and short ones on LITTLE cores.
>>>>>>
>>>>>> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
>>>>>> Reviewed-by: Namhyung Kim <namhyung@kernel.org>
>>>>>> ---
>>>>>>  arch/arm/kernel/topology.c |  153 ++++++++++++++++++++++++++++++++++++++++++++
>>>>>>  1 file changed, 153 insertions(+)
>>>>>>
>>>>> Sorry for not giving this comment on previous version but we should also
>>>>> have a way to provide the big.LITTLE information without Device Tree.
>>>>> May be a platform device/data.
>>>>
>>>> Hi Santosh,
>>>>
>>>> I had thought of adding such additional way to set cpu_power of
>>>> big.LITTLE but my conclusion was
>>>> -it's a new platform so it should come with DT
>>>> -DT is already required by other patches linked to big.LITTLE
>>>> (http://lists.infradead.org/pipermail/linux-arm-kernel/2012-January/080873.html)
>>>> -There is no device that can be easily used to get such information at
>>>> this early boot stage.
>>>>
>>> I see. Its new processor but it is just 1 one of the IP in an entire SOC.
>>> As mentioned below I was talking about full SOC support including
>>> all the driver subsystem with DT.
>>>
>>>>>
>>>>> I know we are moving DT way, but remember apart from core kernel
>>>>> infrastructure, to have a complete product build with DT means all the
>>>>> drivers must be already supporting DT which is not the case with
>>>>> many huge driver sub-systems like USB, display subsystem, Audio etc.
>>>>>
>>>>> Having that support would greatly help for the SOC's which have not yet
>>>>> reached to stage where entire SOC is DT compliant and want to use
>>>>> big.LITTLE infrastructure.
>>>>
>>>> Can't you support both type of devices on your platform ? You can move
>>>> your device to DT mode when it is supported ?
>>>>
>>> That is what eventually people end up doing who don't have
>>> DT ready for entire SOC. I was trying to ask whether at least some
>>> method is proposed(need not be merged in mainline) to have
>>> the big.LITTLE information parsing without DT.
>>
>> Ok, IIUC, you need a temporary methods, which doesn't need to be
>> merged in mainline, to set the cpu_scale field ?
>>
> Yep.

You could use set_power_scale in your platform code to set the
cpu_power of your CPUs until DT is ready for your platform.

Regards,
Vincent

>
> Regards
> Santosh