For those of us who don't know what is involved in power management, would you mind giving a quick explanation of what it involves and why it's painful? What power is there even to manage unless you want to put the computer to sleep or shut it down? Or are those the sole things your are referring to?
Not the OP, but there are many (tens of) "power domains" on the system, and if you care about power/battery life then you want to power each of them down when they're unused, automatically, even while the rest of the system stays running. i.e. why pay the battery life cost for powering a USB hub when there are no USB devices plugged in, or for a DSP when there's no sound being played right now.
But the calculation of when it's safe to power down any of the power domains can be very complicated -- you can't turn off a power supply unless everything that depends on it is unused, so there's a subtle and board-dependent graph/dependency problem to solve.
There's a lot going on in a modern (or even one from 10 years ago) SoC with regards to power management. Just the processor cores themselves can run at different voltages and frequencies, and these are tied to the software workload.
And then you've got the big / little stuff from ARM now, which is an asymmetric multiprocessor, and which cores you use depends on the workload.
At how it works and the interface to it changes from vendor to vendor, sometimes from chip to chip. So it usually isn't implemented all that well, nor is it maintained for very long either.
If (big if) we had more standardized interfaces to this functionality, we could use common drivers that can be upgraded independently.
Like I said, the desktop people may not realize how easy they've got it, where most things are accessed via a standardized bus interface (PCIe or USB). There's no virtuous cycle of software and interface re-use, like there is in desktop land.
Yeah. And arguably this is intentional behavior due to a consequence of ARM's business model, where the SoC vendors all license the same IP and then need to "differentiate" (create incompatible improvements) against each other.
