Hi Paul, > Am 18.06.2023 um 13:51 schrieb Paul Cercueil <paul@xxxxxxxxxxxxxxx>: >> And the issue seems to be that without matching the node names the >> voltages in the device tree may have been ignored completely all the >> time... Now it sets up voltages, which should happen. But different >> ones for my board which breaks boot. > > So the node names fix caused the driver to actually use the info from > DT, which doesn't allow the board to boot. Nice. Very good summary :) As usual the fix is just a one-liner, finding what to do is multi-hours. > >> Finally I did risk (I have no replacement CI20 board and they are no >> longer >> on sale... RS part# was 125-3305 Mouser 456-VL-62851) to run a test >> with >> rename to "DCDC1" but changing the voltage to 1200mV. And this >> version boots. > > Looking at the JZ4780_DS.PDF file, the SoC actually wants 1.1V so the > DT is not wrong - in theory. But in practice it does not work, as you > experienced yourself. However, if the ACT8600 defaults to 1.2V, or if > the bootloader configures it to 1.2V, I would think that this is > actually a voltage that the SoC can handle - otherwise the SoC would be > overvolted until the kernel starts, and the board design would be > flawed. > > I measured that the old 3.x kernel keeps the SoC voltage at 1.2V, so it > sounds like a better default. Therefore the fix here would be to raise > the DCDC1 regulator to 1.2V. I finally found my JZ4780_DS.pdf (Release Date: Nov. 20, 2014). According to Table 3-1 the absolute maximum for VDDcore is 1.21V. According to Table 3-2 the recommended range is 0.99V to 1.21V. 1.1V is only "typical". According to 1.3 Characteristic: "the Core should run at 1.1 -0.1/+0.2V" So 1.1V should be right... But in practise it may be that the ACT8 seems to come up with 1.2V as chip-internal default during boot. Or U-Boot is initializing it as well. Maybe I find some time to measure some test point or capacitor while breaking into U-Boot. BR, Nikolaus
