Subject: [PATCH 03/10] OMAP3: PM: move device-specific special cases from PM core into CPUidle

From: [email-masked] (Kevin Hilman)
Date: Thu, 23 Sep 2010 17:16:14 -0700

Kevin Hilman <[email-masked]> writes:

> Paul Walmsley <[email-masked]> writes:
>
>> Hi Kevin
>>
>> On Tue, 21 Sep 2010, Kevin Hilman wrote:
>>
>>> Paul Walmsley <[email-masked]> writes:
>>> 
>>> > On Wed, 15 Sep 2010, Kevin Hilman wrote:
>>> >
>>> >> In an effort to simplify the core idle path, move any device-specific
>>> >> special case handling from the core PM idle path into the CPUidle
>>> >> pre-idle checking path.
>>> >
>>> > As with the original patch, I don't quite understand the improvement 
>>> > here.  In particular, this part:
>>> >
>>> >> diff --git a/arch/arm/mach-omap2/cpuidle34xx.c b/arch/arm/mach-omap2/cpuidle34xx.c
>>> >> index 3d3d035..0923b82 100644
>>> >> --- a/arch/arm/mach-omap2/cpuidle34xx.c
>>> >> +++ b/arch/arm/mach-omap2/cpuidle34xx.c
>>> >> @@ -233,14 +234,54 @@ static int omap3_enter_idle_bm(struct cpuidle_device *dev,
>>> >>  			       struct cpuidle_state *state)
>>> >>  {
>>> >>  	struct cpuidle_state *new_state = next_valid_state(dev, state);
>>> >> +	u32 core_next_state, per_next_state = 0, per_saved_state = 0;
>>> >> +	u32 cam_state;
>>> >> +	struct omap3_processor_cx *cx;
>>> >> +	int ret;
>>> >>  
>>> >>  	if ((state->flags & CPUIDLE_FLAG_CHECK_BM) && omap3_idle_bm_check()) {
>>> >>  		BUG_ON(!dev->safe_state);
>>> >>  		new_state = dev->safe_state;
>>> >> +		goto select_state;
>>> >> +	}
>>> >> +
>>> >> +	cx = cpuidle_get_statedata(state);
>>> >> +	core_next_state = cx->core_state;
>>> >> +
>>> >> +	/*
>>> >> +	 * Prevent idle completely if CAM is active.
>>> >> +	 * CAM does not have wakeup capability in OMAP3.
>>> >> +	 */
>>> >> +	cam_state = pwrdm_read_pwrst(cam_pd);
>>> >> +	if (cam_state == PWRDM_POWER_ON) {
>>> >> +		new_state = dev->safe_state;
>>> >> +		goto select_state;
>>> >>  	}
>>> >>  
>>> >> +	/*
>>> >> +	 * Prevent PER off if CORE is not in retention or off as this
>>> >> +	 * would disable PER wakeups completely.
>>> >> +	 */
>>> >> +	per_next_state = per_saved_state = pwrdm_read_next_pwrst(per_pd);
>>> >> +	if ((per_next_state == PWRDM_POWER_OFF) &&
>>> >> +	    (core_next_state > PWRDM_POWER_RET)) {
>>> >> +		per_next_state = PWRDM_POWER_RET;
>>> >> +		pwrdm_set_next_pwrst(per_pd, per_next_state);
>>> >> +	}
>>> >> +
>>> >> +	/* Are we changing PER target state? */
>>> >> +	if (per_next_state != per_saved_state)
>>> >> +		pwrdm_set_next_pwrst(per_pd, per_next_state);
>>> >
>>> > In this case, the PER / CORE constraints don't have anything to do with 
>>> > the MPU or CPUIdle, so they don't seem to belong in the CPUIdle code.  The 
>>> > extra comments are certainly nice -- they make it more clear as to what is 
>>> > going on here -- but maybe those can just be added to pm34xx.c ?
>>> 
>>> CPUidle currently manages MPU and CORE powerdomains, so the CORE
>>> constraints seem to make perfect sense here (at least to me.)
>>
>> I do mean CORE also -- basically, anything that is not the CPU.  IMHO 
>> CPUIdle shouldn't manage CORE directly since it's not part of the CPU.  
>> Also since OMAPs have other processors (e.g., DSP, DMA, etc) that can use 
>> the CORE independently of the CPU's power state, it doesn't make sense for 
>> that code to live inside CPUIdle -- probably it should live in some type 
>> of SystemIdle, CORE powerdomain idle or L3 idle.  Again IMHO, the C states 
>> should only represent the MPU's idle state.
>>
>>> The question is probably more about the PER constraints.
>>> 
>>> The basic goal of this is to streamline the core idle (omap_sram_idle())
>>> to be the minimum streamline idle, and to move all the constraint
>>> checking and activity checking to higher layers (like CPUidle.)
>>> Specifically, I'm working towards moving the device-specific idle
>>> constraints out of the core idle path (omap_sram_idle()) and move them
>>> into higher layers where we're checking for activity etc.
>>> 
>>> This is just a baby step towards moving the device-idle out of CPUidle
>>> completely to a place where it can be managed by the driver themeselves
>>> using runtime PM or by using constraints instead of these hard-coded
>>> hacks.
>>
>> I agree completely with the goal; it's the implementation that I don't 
>> like ;-)  But if you agree with the basic idea, that CORE / PER / 
>> whatever-idle should ultimately go elsewhere, since I don't have time to 
>> come up with a constructive alternative at the moment, would you be 
>> willing to just drop a FIXME comment in that code, near the CAM and the 
>> PER / CORE stuff, that mentions that that code should ultimately be 
>> segmented out into its own idle code?
>
> Absolutely...  will do.
>

Here's an updated patch, which will be included in the forthcoming
pm-next pull request.  I updated the changelog with a 'NOTE' and also
added a FIXME in the code.

Thanks for the feedback Paul.

Kevin