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

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Date:	Thu, 11 Feb 2016 16:02:21 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	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 Tuesday 09 February 2016 18:06:26 Daniel Lezcano wrote:
> On 02/09/2016 04:56 PM, Tony Lindgren wrote:
> >* Daniel Lezcano <daniel.lezcano@...aro.org> [160102 14:01]:
> >>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!
> >
> >I'm almost certain those values are not n900 specific but should be
> >used for omap3430 in general.
> >

cpuidle parameters for Nokia N900 were added by this commit:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=5a1b1d3a9efad6bd53d01ff02e86626d1a51d697

which says:

Numbers based on measurements made in October 2009 for PM optimized
kernel with CPU freq enabled.

Tony, do you have any other omap3430 device?

> >>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.
> >
> >While this conversion process is going on, we could just add
> >omap3430_idle_driver and set that based on cpu_is_omap3430()
> >in omap3_idle_init().
> 
> Yes, that could be a temporary alternative.

I would be happy with any solution that allows me to drop my hack patch
from linux-n900 tree.

-- 
Pali Rohár
pali.rohar@...il.com