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

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Date:	Mon, 9 Jul 2012 14:32:20 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
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 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 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 ?

Regards,
Vincent

>
> Regards
> Santosh
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