On 12/17/14, 4:25 AM, Catalin Marinas wrote:
On Wed, Dec 17, 2014 at 12:03:06AM +0000, Al Stone wrote:
That being said, the early systems still don't provide PSCI.
Clarification: some early systems are capable of PSCI but the firmware was in progress (and thus they implemented the Parking Protocol initially but will do full PSCI) - for example AMD Seattle - while one other implementation is unable to provide PSCI and will only do Parking Protocol. Both are trivially supportable through bits in the ACPI MADT.
They will at some point in the future, but not now. Regardless, I think it's reasonable for us to say that if you want ACPI support, PSCI must be used for secondary CPU startup. People can hack something up to get the parking protocol to work on development branches if they want, but I personally see no need to get that into the kernel -- and it needs to be said explicitly in arm-acpi.txt.
That could be ok for upstream - it's up to you guys - but note that there will be some early hardware that doesn't do PSCI. I've sat on *everyone* over the past couple of years behind the scenes to ensure that all future designs will do PSCI, but this takes time to realize.
I'm fine with this. But note that it pretty much rules out the APM boards (I think we ruled them out a few times already) which don't have an EL3 to host PSCI firmware. EL2 is not suitable as it is likely that we want this level for KVM or Xen rather than platform firmware.
The gen1 APM boards work great with UEFI and ACPI using the Parking Protocol. It's trivial to support, and it's a fairly constrained since everyone is headed toward PSCI. Personally I consider it unfair to punish the first guy out of the gate for something that was standardized after they made their design. My recommendation would be to get the relevant document updated in the public repository. Patches that implement Parking Protocol are already in existence/working well as an alternative to PSCI (which is always preferred if available).
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