Re: [PATCH v6 6/6] arm64: Use SYSTEM_OFF2 PSCI call to power off for hibernate

[Oliver Upton <oliver.upton@linux.dev>]

Hi,

On Thu, Oct 24, 2024 at 03:48:26PM +0200, David Woodhouse wrote:
> On 24 October 2024 14:54:41 CEST, Miguel Luis <miguel.luis@oracle.com> wrote:
> >Perhaps spec. F.b. could be accommodated by first invoking SYSTEM_OFF2 with
> >PSCI_1_3_OFF_TYPE_HIBERNATE_OFF and checking its return value in case of a
> >fallback to an invocation with 0x0 ?

This already complies with F.b.

The PSCI implementation is required to accept either 0 or 1 for
HIBERNATE_OFF. Using 0 seems like a good choice for compatibility since ...

> I wasn't aware there was any point. Are there any hypervisors which actually implemented it that way? Amazon Linux and Ubuntu guests already just use zero.
> 
> We could add it later if such a hypervisor (now in violation of F.b) turns up, I suppose?

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);

Thoughts?

-- 
Thanks,
Oliver