Paul Walmsley <paul@xxxxxxxxx> writes:
> Hi Kevin
>
> On Tue, 21 Sep 2010, Kevin Hilman wrote:
>
>> Paul Walmsley <paul@xxxxxxxxx> 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.
Kevin
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