[U-Boot] ARM: PSCI 0.1 vs 0.2

[Marc Zyngier <marc.zyngier@arm.com>]

On 28/11/14 08:52, Jan Kiszka wrote:
> 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?

I seem to remember that you're allowed to return something like "Not
Implemented" (of course, I could be wrong).

But even that is not that hard. I'm pretty sure the i2c pins can be
switched to be GPIOs, and bit-banging i2c is not too difficult (see
drivers/i2c/algos/i2c-algo-bit.c).

I was hoping for something slightly simpler though...

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...