Re: [PATCH v5 03/10] dt-bindings: reserved-memory: Wakeup Mailbox for Intel processors

[Ricardo Neri]

On Mon, Jun 30, 2025 at 09:02:00PM +0200, Rafael J. Wysocki wrote:
> On Sat, Jun 28, 2025 at 5:35 AM Ricardo Neri
> <ricardo.neri-calderon@xxxxxxxxxxxxxxx> wrote:
> >
> > Add DeviceTree bindings to enumerate the wakeup mailbox used in platform
> > firmware for Intel processors.
> >
> > x86 platforms commonly boot secondary CPUs using an INIT assert, de-assert
> > followed by Start-Up IPI messages. The wakeup mailbox can be used when this
> > mechanism is unavailable.
> >
> > The wakeup mailbox offers more control to the operating system to boot
> > secondary CPUs than a spin-table. It allows the reuse of same wakeup vector
> > for all CPUs while maintaining control over which CPUs to boot and when.
> > While it is possible to achieve the same level of control using a spin-
> > table, it would require to specify a separate `cpu-release-addr` for each
> > secondary CPU.
> >
> > The operation and structure of the mailbox is described in the
> > Multiprocessor Wakeup Structure defined in the ACPI specification. Note
> > that this structure does not specify how to publish the mailbox to the
> > operating system (ACPI-based platform firmware uses a separate table). No
> > ACPI table is needed in DeviceTree-based firmware to enumerate the mailbox.
> >
> > Add a `compatible` property that the operating system can use to discover
> > the mailbox. Nodes wanting to refer to the reserved memory usually define a
> > `memory-region` property. /cpus/cpu* nodes would want to refer to the
> > mailbox, but they do not have such property defined in the DeviceTree
> > specification. Moreover, it would imply that there is a memory region per
> > CPU.
> >
> > Co-developed-by: Yunhong Jiang <yunhong.jiang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Yunhong Jiang <yunhong.jiang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> 
> LGTM from the ACPI specification cross-referencing perspective, so
> 
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Thank you Rafael!

I hope this looks good to Krzysztof and Rob too.