linux-kernel - Re: [PATCH v2 2/9] dt-bindings: x86: Add a binding for x86 wakeup mailbox

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Message-ID: <ujfqrllrii6iijlhbwx3bltpjogiosw4xx5pqbcddgpxjobrzh@xqqrfxi5lv3i>
Date: Sun, 25 Aug 2024 09:10:01 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Yunhong Jiang <yunhong.jiang@...ux.intel.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.org, kys@...rosoft.com, haiyangz@...rosoft.com, 
	wei.liu@...nel.org, decui@...rosoft.com, rafael@...nel.org, lenb@...nel.org, 
	kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-hyperv@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 2/9] dt-bindings: x86: Add a binding for x86 wakeup
 mailbox

On Fri, Aug 23, 2024 at 04:23:20PM -0700, Yunhong Jiang wrote:
> Add the binding to use mailbox wakeup mechanism to bringup APs.
> 
> Signed-off-by: Yunhong Jiang <yunhong.jiang@...ux.intel.com>
> ---
>  .../devicetree/bindings/x86/wakeup.yaml       | 64 +++++++++++++++++++
>  1 file changed, 64 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/x86/wakeup.yaml
> 
> diff --git a/Documentation/devicetree/bindings/x86/wakeup.yaml b/Documentation/devicetree/bindings/x86/wakeup.yaml
> new file mode 100644
> index 000000000000..cb84e2756bca
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/x86/wakeup.yaml
> @@ -0,0 +1,64 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +# Copyright (C) 2024 Intel Corporation
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/x86/wakeup.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: x86 mailbox wakeup
> +maintainers:
> +  - Yunhong Jiang <yunhong.jiang@...ux.intel.com>
> +
> +description: |
> +  The x86 mailbox wakeup mechanism defines a mechanism to let the bootstrap
> +  processor (BSP) to wake up application processors (APs) through a wakeup
> +  mailbox.
> +
> +  The "wakeup-mailbox-addr" property specifies the wakeup mailbox address. The
> +  wakeup mailbox is a 4K-aligned 4K-size memory block allocated in the reserved
> +  memory.
> +
> +  The wakeup mailbox structure is defined as follows.
> +
> +    uint16_t command;
> +    uint16_t reserved;
> +    uint32_t apic_id;
> +    uint64_t wakeup_vector;
> +    uint8_t  reservedForOs[2032];
> +
> +  The memory after reservedForOs field is reserved and OS should not touch it.
> +
> +  To wakes up a AP, the BSP prepares the wakeup routine, fills the wakeup
> +  routine's address into the wakeup_vector field, fill the apic_id field with
> +  the target AP's APIC_ID, and write 1 to the command field. After receiving the
> +  wakeup command, the target AP will jump to the wakeup routine.
> +
> +  For each AP, the mailbox can be used only once for the wakeup command. After
> +  the AP jumps to the wakeup routine, the mailbox will no longer be checked by
> +  this AP.
> +
> +  The wakeup mailbox structure and the wakeup process is the same as
> +  the Multiprocessor Wakeup Mailbox Structure defined in ACPI spec version 6.5,
> +  section 5.2.12.19 [1].
> +
> +  References:
> +
> +  [1] https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model.html
> +
> +select: false

This schema is still a no-op because of this false.

What is the point of defining one property if it is not placed anywhere?
Every device node can have it? Seems wrong...

You need to come with proper schema. Lack of an example is another thing
- this cannot be even validated by the tools. 

Best regards,
Krzysztof