Re: Issue with pm_debug?

[Kevin Hilman <khilman@deeprootsystems.com>]

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

> Hello,
>
> I've been studying the power management support on the OMAP 35x EVM (Rev
> G) and have noticed something which seems inconsistent with the
> documentation. 
>
> According to the elinux OMAP Power Management wiki page
> (http://elinux.org/OMAP_Power_Management) - setting "sleep_while_idle"
> to '1' and setting "enable_off_mode" and "voltage_off_while_idle" to '0'
> in the debugfs should result in a kernel which will never hit 'off'
> sleep states. 
>
> However in this set up (with both ladder and menu governor) I've found
> that in this state the C5 and C6 states are entered (according to
> /sys/devices/system/cpu/cpu0/cpuidle/state[5/6]/time). However according
> to the sources these states include the off state. 
>
> Also the /debug/pm_debug/time indicates the off state wasn't reached.
> Therefore is it just the case that the CPUIdle framework requested C5/6
> and the omap driver accepted by actually used another state?

Yes, you're correct.

(also, as an aside, /debug/pm_debug/count might be useful to you as well)

> Is this incorrect behaviour? 

Yes, this is a bug.

This is a known problem in that CPUidle statistics are wrong because
we don't correctly report back to CPUidle the actual state that was
entered when enable_off_mode==0.  Sanjeev has proposed a patch for
this and I have requested some changes from him:

   http://patchwork.kernel.org/patch/62533/

after the changes I have proposed, I plan to merge this into the PM
branch.  We have a similar issue with the recently posted OSWR
support, and Sanjeev's patch will address both dynamic enable of
off-mode and of OSWR.

> Or is my understanding of power management implementation incorrect?
> Any clarifications would be of great value.
>
> I've used the 'pm' branch in the khilman linux-omap-pm repository. (Is
> this the most appropriate mailing list?)

Yes, you're in the right place :)

Thanks for reporting the problem and the thorough analysis.

Kevin