On Tue, Jul 16, 2019 at 09:43:16PM +0300, Dmitry Osipenko wrote: > > CPU parents are PLL_X, PLL_P, and dfll. PLL_X always runs at higher rate > > so switching to PLL_P during CPUFreq probe prior to dfll clock enable > > should be safe. > > AFAIK, PLLX could run at ~200MHz. There is also a divided output of PLLP > which CCLKG supports, the PLLP_OUT4. > > Probably, realistically, CPU is always running off a fast PLLX during > boot, but I'm wondering what may happen on KEXEC. I guess ideally > CPUFreq driver should also have a 'shutdown' callback to teardown DFLL > on a reboot, but likely that there are other clock-related problems as > well that may break KEXEC and thus it is not very important at the moment. > If you turn off the DFLL, you have to be aware that the voltage margins for DFLL use are lower than for PLL use. So you either need to be sure to switch to a frequency below fmax @ Vmin or you program the boot voltage and then you can use PLLX as setup by the bootloader. For OVR regulators you can't program a voltage without the DFLL, so you have to tristate the PWM output which will give you a hardwired boot voltage. Peter.
