linux-kernel - Re: Nokia N900: Proper C-states

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Date:	Sat, 2 Jan 2016 23:00:48 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Pali Rohár <pali.rohar@...il.com>,
	Tony Lindgren <tony@...mide.com>
Cc:	Jean Pihet <j-pihet@...com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kevin Hilman <khilman@...com>, Nishanth Menon <nm@...com>,
	Pavel Machel <pavel@....cz>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Sebastian Reichel <sre@...nel.org>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>
Subject: Re: Nokia N900: Proper C-states

On 01/02/2016 03:26 PM, Pali Rohár wrote:
> Hello,
>
> due to this Daniel Lezcano commit (ARM: OMAP3: cpuidle - remove rx51
> cpuidle parameters table)
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=231900afba52d6faddfb480cde4132d4edc089bc
>
> we need patch cpuidle34xx.c code to fix commit for Nokia N900. See:
>
> https://github.com/pali/linux-n900/commit/e147fd4b678f1f3d7a5235287910960bd41e04dc
>
> As Nokia N900 code is converting from legacy board code to DST, I would
> like to know how to patch correctly omap3_idle_driver in DTS with
> correct values measured for Nokia N900. Thanks!

Hi Pali,

the conversion to the DT based arm cpuidle driver could be a bit complex 
with one issue (index 0 != cpu_do_idle()) and one performance regression 
(cpu_pm_enter/exit will be called in retention mode, even if this is not 
needed).

It will result in a PM code only on one side and on the other side, the 
generic cpuidle-arm.c driver will be used instead with the DT 
definition. It is worth to the conversion because the result will be 
nice IMO.

Added Lorenzo who is initially author of the arm generic driver. We 
already discussed in the past about those two issues above and I think 
this is something we should improve.



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