On 24 October 2024 21:57:38 CEST, Oliver Upton <oliver.up...@linux.dev> 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.up...@linux.dev>
>> 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.
