Messages in this thread | | | Subject | Re: [PATCH] ARM: dts: imx6sx-sdb: Remove cpufreq OPP override | From | Marek Vasut <> | Date | Wed, 3 May 2017 21:33:24 +0200 |
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On 05/03/2017 07:58 PM, Leonard Crestez wrote: > On Wed, 2017-05-03 at 17:59 +0200, Marek Vasut wrote: >> On 05/03/2017 04:58 PM, Leonard Crestez wrote: >>> On Wed, 2017-05-03 at 16:26 +0200, Marek Vasut wrote: >>>> 2) It actually fixes a problem with the voltage rails such that the DVFS >>>> works without leaving the system in unstable or dead state. You do >>>> need the second part of my patch if you drop the OPP hackery, without >>>> it the power framework cannot correctly configure the core voltages, >>>> so the patch from Leonard makes things worse. >>> No, I think there is a misunderstanding here. The second part of your >>> patch will cause cpufreq poking at LDOs to indirectly adjust the input >>> from the PMIC to the minimum required (this is LDO target + >>> min_dropout_uv). Without it by default VDD_ARM_SOC_IN will remain fixed >>> as 1375mV from boot. > >> Who sets / guarantees that default value for ARM and SOC rails ? > > I think it's from the PMIC hardware itself (but maybe uboot plays with > it). VDD_ARM_SOC_IN on this board is tied to SW1AB from MMPF0200: > > http://www.nxp.com/assets/documents/data/en/data-sheets/MMPF0200.pdf > > It seems reasonable to rely on such voltages set externally.
Isn't it an established rule that Linux should not depend on bootloader settings ? Or did that change ?
>> With the OPP override in place, there's at least the guarantee that both >> rails will have the same voltage requirement. If you remove the OPP >> override without modeling the actual regulator wiring, the guarantee is >> gone. > > The imx6sx chip has internal LDO_ARM and LDO_SOC regulators which can > generate separate voltages for arm/soc. The fact that these regulators > share the same supply is only an issue when they are set in bypass > mode. > > However the boot issues happen on REV C but apparently not REV B of the > board. I don't have a good explanation for this so maybe I am missing > something.
Well the regulator(s) cannot be correctly configured if the kernel doesn't have the correct power distribution described in the DT .
-- Best regards, Marek Vasut
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