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

[Sudeep Holla <sudeep.holla@kernel.org>]

On Tue, Jul 21, 2026 at 02:04:05PM +0100, Mark Rutland wrote:
> 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.
> 

+1

> > 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@J2N7QTR9R3.cambridge.arm.com/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.
>

+1

Just curious if CPU_OFF on this CPU0 returns DENIED or just proceeds and
ends up with cpu and/or system hang ?

-- 
Regards,
Sudeep