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