On Mon, Jan 22, 2024 at 6:44 PM Jonathan Cameron
[off-list ref] wrote:

On Mon, 18 Dec 2023 21:30:50 +0100
"Rafael J. Wysocki" [off-list ref] wrote:

quoted

On Wed, Dec 13, 2023 at 1:49 PM Russell King [off-list ref] wrote:

quoted

From: James Morse <james.morse@arm.com>

To allow ACPI to skip the call to arch_register_cpu() when the _STA
value indicates the CPU can't be brought online right now, move the
arch_register_cpu() call into acpi_processor_get_info().

This kind of looks backwards to me and has a potential to become
super-confusing.

I would instead add a way for the generic code to ask the platform
firmware whether or not the given CPU is enabled and so it can be
registered.

Hi Rafael,

The ACPI interpreter isn't up at this stage so we'd need to pull that
forwards. I'm not sure if we can pull the interpreter init early enough.

Well, this patch effectively defers the AP registration to the time
when acpi_processor_get_info() runs and the interpreter is up and
running then.

For consistency, it would be better to defer the AP registration in
general to that point.

Perhaps pushing the registration back in all cases is the way to go?
Given the acpi interpretter is initialized via subsys_initcall() it would
need to be after that - I tried pushing cpu_dev_register_generic()
immediately after acpi_bus_init() and that seems fine.

Sounds promising.

We can't leave the rest of cpu_dev_init() that late because a bunch
of other stuff relies on it (CPU freq blows up first as a core_init()
on my setup).

I see.

So to make this work we need it to always move the registration later
than the necessary infrastructure, perhaps to subsys_initcall_sync()
as is done for missing CPUs (we'd need to combine the two given that
needs to run after this, or potentially just stop checking for acpi_disabled
and don't taint the kernel!).  I think this is probably the most consistent
option on basis it at least moves the registration to the same point
whatever is going on and can easily use the arch callback you suggest
to hide away the logic on deciding if a CPU is there or not.

I agree.