Greetings Kevin/Paul,
We have been working to understand omap powerdomain concepts. We used a couple
of use cases (i.e. cpuidle, cpufreq etc.) to see how omap handles them. We saw
that the leaf functions in such use cases interact with defined
powerdomain/clockdomain that talks with hardware directly (pwrdm->prcm_offs /
clkdm1->prcm_partition, clkdm->clkdm_offs).
For example, in for omap2/3 archs, the powerdomain are declared in
powerdomains3xxx_data.c
/* As powerdomains are added or removed above, this list must also be changed */
static struct powerdomain *powerdomains_omap3xxx[] __initdata = {
&wkup_omap2_pwrdm,
&gfx_omap2_pwrdm,
&iva2_pwrdm,
&mpu_3xxx_pwrdm,
&neon_pwrdm,
&core_3xxx_pre_es3_1_pwrdm,
....
};
The same goes for both voltagedomains and clockdomains.
In the cpuidle scenario, in omap3_enter_idle function,
1. it sets next power state for the particular power domain using
pwrdm_set_next_pwrst
2. it sets clock state for the particular clock domain using
pwrdm_for_each_clkdm
With that being said, would you please help us understand following,
1.
It seems that all three concepts, voltagedomains, powerdomains, and
clockdomains, are tightly coupled with the OMAP hardware. Were these concepts
derived exclusive keeping omap hardware in perspective? Or How would you say
that any OEM can implement such concepts, or would it make sense?
2.
As shown in following diagram, each voltagedomain contains one or many
powerdomains, each powerdomain contains one or many clockdomains, and each
clockdomain, in turn, would correspond to one or many clocks.
|-cldm1 |-clock1
vltdm1 --|-pwrdm1----|-clkdm2---|-clock2
| |-cldm_n |-clock_n
|-pwrdm2
|
|-pwrdm_n
The question is how would describe a situation in which same needs to be
sourced for multiple powerdomains? or is it so that you make sure such relation
does happen while chip is being laid out?
3.
What is the meaning of following two terms (taken from powerdomain.h),
* @prcm_offs: the address offset from CM_BASE/PRM_BASE
* @prcm_partition: (OMAP4 only) the PRCM partition ID containing @prcm_offs
4.
This might be a stupid question, but I'll ask anyway. :)
How do you define MPU? How different it is from CPU?
How do you differentiate between MPU and core?
5.
Currently we are working on linaro-pm branch of linux-pm tree. Would you advise
us use rather another branch for this work, if any?
Thanks,
Jay
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