[U-Boot] ARMv8 switching CPUs into EL1

[U-Boot] ARMv8 switching CPUs into EL1

[Mels van Broekhoven]

L.S.!

On a Xilinx ZynqMP-based platform with u-boot running in Aarch64 mode in
EL2, after booting a Linux kernel  in EL1 using CONFIG_ARMV8_SWITCH_TO_EL1,
Linux throws a warning that the CPUs have started in inconsistent modes
("CPU: CPUs started in inconsistent modes").
Indeed, only the first core on which U-boot was running is switched to EL1
at this point.

Is this a bug or a not completely supported feature in U-boot or can this
warning actually be safely ignored under certain circumstances?

Kind regards,

Mels

[U-Boot] ARMv8 switching CPUs into EL1

[Lukasz Majewski]

Hi Mels,

> L.S.!
> 
> On a Xilinx ZynqMP-based platform with u-boot running in Aarch64 mode
> in EL2, after booting a Linux kernel  in EL1 using
> CONFIG_ARMV8_SWITCH_TO_EL1, Linux throws a warning that the CPUs have
> started in inconsistent modes ("CPU: CPUs started in inconsistent
> modes"). Indeed, only the first core on which U-boot was running is
> switched to EL1 at this point.
> 
> Is this a bug or a not completely supported feature in U-boot or can
> this warning actually be safely ignored under certain circumstances?
> 

U-boot by design starts on Core0. Other cores are not touched and are
managed (started/configured) by Linux.

The other question is if you use the ARM Trusted Firmware [ATF]. If you
start/load it in U-Boot (or any earlier bootloader), then it also may
change / configure CPUs state.

> Kind regards,
> 
> Mels
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> https://lists.denx.de/listinfo/u-boot




Best regards,

Lukasz Majewski

--

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[U-Boot] ARMv8 switching CPUs into EL1

[Michal Simek]

Hi,

On 06. 06. 19 15:15, Mels van Broekhoven wrote:
> L.S.!
> 
> On a Xilinx ZynqMP-based platform with u-boot running in Aarch64 mode in
> EL2, after booting a Linux kernel  in EL1 using CONFIG_ARMV8_SWITCH_TO_EL1,
> Linux throws a warning that the CPUs have started in inconsistent modes
> ("CPU: CPUs started in inconsistent modes").
> Indeed, only the first core on which U-boot was running is switched to EL1
> at this point.
> 
> Is this a bug or a not completely supported feature in U-boot or can this
> warning actually be safely ignored under certain circumstances?

I have take a look at the path and what it is happening is that ATF
records that cpu0 started in EL2. Then u-boot starts Linux in EL1
because of macro above. And then Linux is asking from EL1 ATF to turn on
CPU but ATF has a record that CPU0 started in EL2 that's why it starts
others cpus in EL2. And then Kernel reports back that it is not consistent.

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Xilinx Microblaze
Maintainer of Linux kernel - Xilinx Zynq ARM and ZynqMP ARM64 SoCs
U-Boot custodian - Xilinx Microblaze/Zynq/ZynqMP/Versal SoCs


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[U-Boot] ARMv8 switching CPUs into EL1

[Mark Kettenis]

> From: Michal Simek <monstr@monstr.eu>
> Date: Tue, 11 Jun 2019 14:09:29 +0200
> 
> Hi,
> 
> On 06. 06. 19 15:15, Mels van Broekhoven wrote:
> > L.S.!
> > 
> > On a Xilinx ZynqMP-based platform with u-boot running in Aarch64 mode in
> > EL2, after booting a Linux kernel  in EL1 using CONFIG_ARMV8_SWITCH_TO_EL1,
> > Linux throws a warning that the CPUs have started in inconsistent modes
> > ("CPU: CPUs started in inconsistent modes").
> > Indeed, only the first core on which U-boot was running is switched to EL1
> > at this point.
> > 
> > Is this a bug or a not completely supported feature in U-boot or can this
> > warning actually be safely ignored under certain circumstances?
> 
> I have take a look at the path and what it is happening is that ATF
> records that cpu0 started in EL2. Then u-boot starts Linux in EL1
> because of macro above. And then Linux is asking from EL1 ATF to turn on
> CPU but ATF has a record that CPU0 started in EL2 that's why it starts
> others cpus in EL2. And then Kernel reports back that it is not consistent.

I'd say the answer in this situation is that you really shouldn't use
the CONFIG_ARMV8_SWITCH_TO_EL1 in your configuration if you're using
ATF.  Or you should configure ATF such that it spins up the secondary
CPUs into EL1.  Not sure if there is an easy way to do that though.