18.07.2019 23:11, Dmitry Osipenko пишет: > 18.07.2019 22:24, Sowjanya Komatineni пишет: >> >> On 7/18/19 12:18 PM, Peter De Schrijver wrote: >>> 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. >> >> Yes, we switch CPU to PLLP and then disable DFLL during suspend. > > I'm wondering what happens to T124 on resume from suspend, given that it > switches CPU to PLLX [1]. I imagine that CPU voltage could be lower than > needed if suspend happened on DFLL. I'm also now vaguely recalling that > CPUFreq driver was disabled for T124 because of some problems. > > Or maybe warmboot code is actually touching the voltage regulators? Oh wait, warmboot is even irrelevant LP1. > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/arch/arm/mach-tegra/sleep-tegra30.S#n389 > > That is also should be a problem for T30 if voltage scaling is happening > and I have some patches in works that are switching CPU to PLLP instead > of PLLX on suspend/resume. >
