linux-kernel - Re: [PATCH v4 3/5] ARM: topology: Update cpu

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Date:	Mon, 9 Jul 2012 18:30:01 +0530
From:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linaro-dev@...ts.linaro.org, devicetree-discuss@...ts.ozlabs.org,
	linux@....linux.org.uk, a.p.zijlstra@...llo.nl,
	grant.likely@...retlab.ca, rob.herring@...xeda.com,
	yong.zhang0@...il.com, namhyung@...nel.org,
	jean.pihet@...oldbits.com
Subject: Re: [PATCH v4 3/5] ARM: topology: Update cpu_power according to DT information

On Mon, Jul 9, 2012 at 6:02 PM, Vincent Guittot
<vincent.guittot@...aro.org> wrote:
> On 9 July 2012 12:55, Shilimkar, Santosh <santosh.shilimkar@...com> wrote:
>> Vincent,
>> On Mon, Jul 9, 2012 at 2:57 PM, Vincent Guittot
>> <vincent.guittot@...aro.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@...aro.org>
>>> Reviewed-by: Namhyung Kim <namhyung@...nel.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.

Regards
Santosh
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