On 24 October 2024 21:57:38 CEST, Oliver Upton <oliver.upton@xxxxxxxxx> wrote: >On Thu, Oct 24, 2024 at 05:56:09PM +0200, David Woodhouse wrote: >> On 24 October 2024 17:44:49 CEST, Oliver Upton <oliver.upton@xxxxxxxxx> wrote: >> >IIUC, you're really wanting to 0x0 because there are hypervisors out >> >there that violate the final spec and *only* accept this value. >> > >> >That's perfectly fine, but it'd help avoid confusion if the supporting >> >comment was a bit more direct: >> > >> > /* >> > * If no hibernate type is specified SYSTEM_OFF2 defaults to >> > * selecting HIBERNATE_OFF. >> > * >> > * There are hypervisors in the wild that violate the spec and >> > * reject calls that explicitly provide a hibernate type. For >> > * compatibility with these nonstandard implementations, pass 0 >> > * as the type. >> > */ >> > if (system_entering_hibernation()) >> > invoke_psci_fn(PSCI_FN_NATIVE(1_3, SYSTEM_OFF2), 0 , 0, 0); >> >> By the time this makes it into released versions of the guest Linux kernel, that comment won't be true any more. > >Then does it even matter? What is the problem you're trying to solve >with using a particular value for the hibernate type? > >Either the goal of this is to make the PSCI client code compatible with >your hypervisor today (and any other implementation based on 'F ALP1') or >we don't care and go with whatever value we want. > >Even if the comment eventually becomes stale, there is a ton of value in >documenting the exact implementation decision being made. > Eventually it won't matter and we can go with whatever value we want. But yes, the goal is to be compatible with the hypervisor *today* until it catches up the changes to the final versions of the spec. I didn't spend much time overthinking the comment. What was it.... /* * Zero is an acceptable alternative to PSCI_1_3_OFF_TYPE_HIBERNATE_OFF * and is supported by hypervisors implementing an earlier version * of the pSCI v1.3 spec. */ That seems to cover it just fine, I think.
