Re: PM: VDD2 OPPs

[Kevin Hilman <khilman@deeprootsystems.com>]

"Andrew Murray" <amurray@mpc-data.co.uk> writes:

[...]

> I've noticed that other than using the debugfs there is no way for a
> user to configure sleep_when_idle, enable_off_mode,
> voltage_off_when_idle. Do you think it would be worthwhile to add
> these options to the KConfigs? I'd be happy to make these
> modifications if so.  :)

Hi Andrew,

I'm curious what benefit you to having them as compile-time options
instead of run-time?

In general, these options are all under debugfs for debug during PM
development, but they should not be considered as PM knobs for a
production system.

For a production system, the assumption is that the kernel is *always*
trying to sleep-while-idle and enter off-mode.  Preventing low-power
states is intended to be directed by drivers using constraints
(latency, throughput, etc.)  When using constraints, the deeper sleep
states are prevented while the constraints are in place and then
(re)allowed after the constraints are removed.

Kevin



>
> Many Thanks,
>
> Andrew Murray
> 	
> -----Original Message-----
> From: Nishanth Menon [mailto:nm@ti.com] 
> Sent: 26 January 2010 20:41
> To: Andrew Murray
> Cc: linux-omap@vger.kernel.org
> Subject: Re: PM: VDD2 OPPs
>
> Andrew Murray had written, on 01/26/2010 02:34 PM, the following:
>> Hello,
>> 
>> With regards to the OMAP2 (or at least the 3530 EVM) -the TRM and
>> various whitepapers suggest that they are 3 OPP levels available for
>> VDD2 (L3). However, from looking at the sources (linux-omap-pm / pm
>> branch) it seems that only 2 OPP levels are supported (@166Mhz and
>> @83Mhz) and used. I also notice that these rates are different to
> those
>> in a whitepaper (166, 100 and 41.5). Is there any particular reason
> why
> on OMAP34/35xx, I believe it should be s/100/83/.
>> only 2 OPPs are used? 
> to my knowledge 41.5Mhz is not known to provide any performance 
> benefits. you can also see [1] and add 41.5 (pm-wip-opp is the new 
> branch where we are introducing opp layer.
>
>> 
>> I understand that the OPP level of VDD2 may be set by changes to the
> OPP
>> level of VDD1 (i.e. resource34xx.c:set_opp) - and modifying VDD1's OPP
>> via cpufreq seems to be the only way to adjust the VDD2 OPP from
>> user-land - is this correct?
> The old /sys/power/vdd2_[opp|lock] was deprecated out. currently the 
> control is for vdd1 OPP using cpufreq and indirect dependency for VDD2, 
> is there a need for direct control of VDD2 freq?
> -- 
> Regards,
> Nishanth Menon
>
> Ref:
> [1] 
> http://git.kernel.org/?p=linux/kernel/git/khilman/linux-omap-pm.git;a=bl
> ob;f=arch/arm/mach-omap2/cpufreq34xx.c;h=07873e87ffc0fef97b4554efc3f17dc
> 696cb25e3;hb=4f54a09e0ed9b2ee8e1adfe1716297792310d1c6#l46
>
>
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