- Discussion
So this clearly shows that the heat production in the CPU depends on the device tree file and if the mainboard is connected or not.
This is REALLY weird. Why should the OMAP5 produce more heat simply because the mainboard is connected? It doesn't do anything with the additional connected devices if no driver is configured. Unless... could it be that it sees there's something there (like on i2c bus) and it tries to permanently probe that? But then again, it would need to be something that has nothing to do with load, as you're putting the OMAP5 on high load anyways.
We have 31 sec with pyra mainboard and pyra DT
So it heats up three times as fast simply because the mainboard is connected and MIPI is active? That sounds like WAY too much. It shouldn't have much impact.
40 sec without pyra mainboard and pyra DT
Wow! Still twice as fast. Some bug with the DT file maybe?
42 sec with pyra mainboard and uevm DT
... combined with something that the mainboard does?
100 sec without pyra mainboard and uevm DT
This is of course to be expected since the uevm.dtb does not know anything about panels and Pyra peripherals and therefore does not enable anything -
and does not have to process polling loops etc.
Is that the way the DT file works? Does it poll until it finds everything? No timeout, etc.?
Because usually Linux checks for the devices and that's it. It doesn't constantly poll. Well, that would explain the faster heat up when using Pyras DT file without the mainboard attached - but then again, polling is being done by the CPU which is already under high load, so the polling shouldn't make any difference at all.
So something really weird is going on there.
Having the additional components (mainboard) simply connected shouldn't heat up the OMAP5 at all, unless it does something actively with them (which it shouldn't). Yes, the PALMAS needs to provide power for them, so that one might heat up a bit more, but the OMAP5 shouldn't, when everything is properly setup.
So for me, this raises the following questions:
1. Why does the OMAP5 heat up when the mainboard is attached? It really shouldn't do that, unless it actively uses any of these added components.
2. Why does the MIPI stream produce THAT much more heat? Based on the temperature rising, it needs... almost the same amount as both cores under full load? That can't be right.
But if we assume that the scenario 1 has the highest energy consumption, it explains why it is more risky to run into power supply limits.
Yes, but raises the question why so much more energy is needed. It shouldn't really add much!
Is the software setup causing that? Could there be a hardware issue on the mainboard that could cause the OMAP5 to heat up for some reason?
Realistically, the heating difference in my opinion shouldn't be more than 5 - 10 seconds. And you even have a 70 seconds difference with the Pyra.dt setup and mainboard connected. That's WAY too high (and also explains why I always thought the prototype heats up way too fast).
When doing absolutely nothing, it shouldn't really warm up at all, but it's clearly noticeable.
So something (hardware, software, whatever) on the mainboard causes the OMAP5 to heat up immensively, and we need to find that part and check what's wrong with it!