Re: [PATCH v2] arm64: Disallow disabling boot CPU based on config

[Mark Rutland]

On Tue, Jul 21, 2026 at 12:29:54PM +0530, Sneh Mankad wrote:
> On 03-Jul-26 7:58 PM, Mark Rutland wrote:
> > On Fri, Jul 03, 2026 at 04:50:02PM +0530, Sneh Mankad wrote:
> 
> FW permits CPU0 disablement because it functions properly in regular run time.
> But there is an additional hardware constraint in above mentioned platforms, that
> suspend to ram has to be performed via boot CPU / CPU0. Due to this constraint,
> CPU0 is required to be online when suspend to ram is triggered.

The PSCI spec doesn't permit that.

Even if HW has that constraint, it's up to FW to hide that from the OS.

[...]

> > This is a platform-specific property, and it's possible to build a
> > kernel that boots on this platform and/or other platforms.
> 
> Yes, but for that reason the config will only be enabled for SoCs that have this
> constraint, it will remain disabled for other SoCs.

Please re-read what I said. A config option can't help if you have a
single kernel that supports multiple platforms.

> As mentioned above, its not a FW bug. CPU0 is allowed to be disabled
> from FW and HW constraint is for suspend to ram to be performed on
> boot CPU.

Please see my other reply at:

  https://lore.kernel.org/linux-arm-kernel/al9tdvOxYb83zBxd@xxxxxxxxxxxxxxxxxxxxxxxxxxxx/T/#m872da3cc4ded3386dce92d4bd4bdf9c33d3e2d0b

This is *definitely* a firmware bug.

To be clear, I'm not saying we can't do something to address that, but
let's not pretend that this is compliant with the PSCI spec.

Mark.