I have some more questions inline..
Note that the previous patches I have submitted so far are not tight
to freq table values (any freq values can be selected).
> 1.
> In the Linux kernel the available MPU frequencies and voltages are
> listed in > arch/arm/mach-omap2/opp4xxx_data.c in the struct >
omap_opp_defq.
> Considering that the MPU can be driven by all the different
frequencies that
> someone can generate on the dpll why only 4 frequencies are listed?
> Is it due to the fact that there are only 4 voltage domains availables?
> Can I add other frequency values?
OPP = frequency + voltage
For any given frequency there is a minimum voltage which must be
applied for the IP to operate within spec. Conversely for any given
voltage there is a maximum frequency which an IP can operate at while
staying within spec.
It is true that you can lock the MPU's PLL at many different
frequencies, but we have only validated a small number of
frequency+voltage combinations. It is advisable to stick with ones
provided in the OPP table so that there are no timing violations or
under-voltage issues.
Will the smartreflex driver select the best voltage for me at any
time? How can I verify that the smartreflex is actually running? Is
there a device driver in the Linux source tree?
> 2.
> Cpufreq helps the user switching between different frequencies value.
> Frequency switching can help saving power. Switching frequency
lets the core
> running at a different voltage, how can I also switch to the
correct voltage
> domain? Voltage scaling is not taken into account in the cpufreq driver?
> Will the SmartReflex technology help me? please can you elaborate more on
> this point, pointing me on the OMAP4 pdf documentation? How can I switch
> frequency and voltage together to save the maximum power?
As a general rule, since you are interested in power management, your
best friend is Chapter 3 of the TRM, "Power, Reset and Clock
Management". I know that Chapter 4 looks good since it is the MPU,
but Chapter 3 contains everything you need to know about PM.
Kevin's patches will scale voltage as a part of the CPUfreq drivers
.target call.
I went through Kevin's patches but I cannot see any voltage scaling in
cpufreq related stuff, can you please point me out on the exact code?
Function trace on which I have went through:
drivers/cpufreq/cpufreq.c: __cpufreq_driver_target
drivers/cpufreq/omap-cpufreq.c: omap_target
arch/arm/plat-omap/clock.c: clk_set_rate
arch/arm/mach-omap2/clock.c: omap2_clk_set_rate
arch/arm/mach-omap2/dpll3xxx.c: omap3_noncore_dpll_set_rate
> 5.
> From SWPU231K I understand that each CPU is a power domain so I can change
> power state of each CPU independently. Is there a simple way to
put one core
> to dormant or power-off mode in Linux?
You can turn off CPU1 (but not CPU0) with,
echo 0 > /sys/devices/system/cpu/cpu1/online
And bring it back up with,
echo 1 > /sys/devices/system/cpu/cpu1/online
This will migrate all work on CPU1 over to CPU0 and take the CPU1
power domain to the lowest power state, OFF mode.
Wow! This work very well! Measuring power on my PandaBoard when
switching off CPU1 I do not see any power difference! Why?
Thanks,
Antonio
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