[U-Boot] ARM: PSCI 0.1 vs 0.2

[Jan Kiszka]

On 2014-11-10 14:36, Marc Zyngier wrote:
> On 10/11/14 13:25, Jan Kiszka wrote:
>> On 2014-11-10 14:08, Marc Zyngier wrote:
>>> On 10/11/14 12:51, Jan Kiszka wrote:
>>>> Hi Marc,
>>>>
>>>> what is the motivation to expose a PSCI 0.1 interface in U-boot, instead
>>>> of 0.2? Support for preexisting users of 0.1? The kernel seems to be
>>>> happy with both, and I'm now wondering if we should actually add the
>>>> legacy version to Jailhouse as well (I hope we can avoid this).
>>>
>>> The initial rational was simple: at the time this code was written, the
>>> 0.2 spec still in review, and nobody was implementing it. Supporting 0.1
>>> was the only viable use-case.
>>>
>>>> Still studying the logic: Is it possible to provide both interfaces, and
>>>> would it make sense?
>>>
>>> Supporting both is very easy. Just output the 0.2 function numbers that
>>> actually make sense for 0.1 and have both compatible strings.
>>
>> Ah, cool - parameters and return values of, say, CPU_ON/OFF are
>> compatible across both versions?
> 
> That was the idea of the spec (broadly compatible across revisions...).

There is one major problem with v0.2, though, and I bet this also
applies to the ARMv8 implementation:

v0.2 mandates that the firmware provides SYSTEM_RESET - that's rather
simple - and SYSTEM_OFF. The latter seems non-trivial for the sunxi as
the power controller is attached via i2c. I guess that will be quite a
bit of code in the PSCI monitor for a feature that already works fine
for Linux with v0.1. Or am I missing something?

Jan


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