Re: [Qemu-devel] [RFC v1 2/2] arm: boot: Add EL jump-down code for Linux

[Peter Crosthwaite]

On Tue, Sep 2, 2014 at 8:56 AM, Peter Maydell <address@hidden> wrote:
> On 1 September 2014 23:41, Peter Crosthwaite
> <address@hidden> wrote:
>> On Tue, Sep 2, 2014 at 3:15 AM, Peter Maydell <address@hidden> wrote:
>>> On 19 August 2014 01:54, Peter Crosthwaite <address@hidden> wrote:
>>>> Linux should boot in EL2 or EL1. If in EL3, jump down before handing
>>>> off to Linux.
>>>>
>>>> Signed-off-by: Peter Crosthwaite <address@hidden>
>>>
>>> The other way we could do this would be to have the
>>> do_cpu_reset() hook put the CPU into EL2 or EL1 before
>>> starting the boot code. (This would be in line with how it
>>> would work for KVM).
>>>
>>
>> Tried that at first, and the problem we found was it introduced a
>> reset order dep. The arm-boot and CPU race on who sets the EL.
>
> Surely there's already a reset order dependency, because
> both the arm-boot reset hook and CPU reset proper want
> to initialise the PC ?
>

Yes. I had a PC specific solution to this though when it became a
problem. I have another series that made the reset ordering a little
less predictable (specifically implementation of CPU reset GPIOs). So
i'm trying to reduce the footprint of this issue as much as possible.

Regards,
Peter

>>> Have you thought about how this would work for
>>> secondary CPUs (which boot via PSCI poweron)?
>
>> Not yet although I expect something similar.
>
> Hmm. I guess PSCI poweron won't even go through
> the boot.c code, thinking a bit more about it. I need to
> look at the TCG PSCI patches too.
>
> -- PMM
>