linux-kernel - Re: [PATCH v2] AM3517 : support for suspend/resume

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Date:	Fri, 23 Sep 2011 09:07:59 -0700
From:	Kevin Hilman <khilman@...com>
To:	"Koyamangalath\, Abhilash" <abhilash.kv@...com>
Cc:	"linux-omap\@vger.kernel.org" <linux-omap@...r.kernel.org>,
	"tony\@atomide.com" <tony@...mide.com>,
	"linux\@arm.linux.org.uk" <linux@....linux.org.uk>,
	"V\, Aneesh" <aneesh@...com>,
	"Shilimkar\, Santosh" <santosh.shilimkar@...com>,
	"Menon\, Nishanth" <nm@...com>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"Lohithakshan\, Ranjith" <ranjithl@...com>
Subject: Re: [PATCH v2] AM3517 : support for suspend/resume

"Koyamangalath, Abhilash" <abhilash.kv@...com> writes:

[...]

>>> @@ -485,6 +489,8 @@ console_still_active:
>>>
>>>  int omap3_can_sleep(void)
>>>  {
>>> +     if (cpu_is_omap3505() || cpu_is_omap3517())
>>> +             return 0;
>>
>> This needs to be a separate patch with a descriptive changelog and
>> justification as to why you can't do WFI in idle.
> [Abhilash K V]OK
>>
>> Adding something like this means the device will *never* attempt a WFI
>> during idle.
>
> [Abhilash K V] This patch was put in as dynamic sleep feature is not
> supported by the device, there are no C states etc. The only PM
> supported is forced suspend /resume. There is just one power-domain
> and it can be in ON or RET states.
>

If the device can WFI and hit retention in suspend, there should be no
not to target the same power state in idle.

You don't have to have CPUidle with multiple C-states to use idle.

>> I suspect that avoiding WFI in idle is masking a bug that you don't see
>> in the suspend path.
>
> [Abhilash K V] I need to recap a bit to find out if there is a better
> way to indicate the lack of "idle" feature.

Yes please.  From my POV, deciding not to go idle is a SW decision, not
a hardware decision.  As the same SW mechanisms are involved, whatever
power state that can be acheived from suspend should be targetted in
idle.

Kevin

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