linux-kernel - [PATCH v6 14/14] Documentation: KHO: Add memblock bindings

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Message-ID: <20250411053745.1817356-15-changyuanl@google.com>
Date: Thu, 10 Apr 2025 22:37:45 -0700
From: Changyuan Lyu <changyuanl@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: akpm@...ux-foundation.org, anthony.yznaga@...cle.com, arnd@...db.de, 
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	will@...nel.org, x86@...nel.org, Changyuan Lyu <changyuanl@...gle.com>
Subject: [PATCH v6 14/14] Documentation: KHO: Add memblock bindings

From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>

We introduced KHO into Linux: A framework that allows Linux to pass
metadata and memory across kexec from Linux to Linux. KHO reuses fdt
as file format and shares a lot of the same properties of firmware-to-
Linux boot formats: It needs a stable, documented ABI that allows for
forward and backward compatibility as well as versioning.

As first user of KHO, we introduced memblock which can now preserve
memory ranges reserved with reserve_mem command line options contents
across kexec, so you can use the post-kexec kernel to read traces from
the pre-kexec kernel.

This patch adds memblock schemas similar to "device" device tree ones to
a new kho bindings directory. This allows us to force contributors to
document the data that moves across KHO kexecs and catch breaking change
during review.

Co-developed-by: Alexander Graf <graf@...zon.com>
Signed-off-by: Alexander Graf <graf@...zon.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
Signed-off-by: Changyuan Lyu <changyuanl@...gle.com>
---
 .../kho/bindings/memblock/memblock.yaml       | 39 ++++++++++++++++++
 .../kho/bindings/memblock/reserve-mem.yaml    | 40 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 3 files changed, 80 insertions(+)
 create mode 100644 Documentation/core-api/kho/bindings/memblock/memblock.yaml
 create mode 100644 Documentation/core-api/kho/bindings/memblock/reserve-mem.yaml

diff --git a/Documentation/core-api/kho/bindings/memblock/memblock.yaml b/Documentation/core-api/kho/bindings/memblock/memblock.yaml
new file mode 100644
index 0000000000000..d388c28eb91d1
--- /dev/null
+++ b/Documentation/core-api/kho/bindings/memblock/memblock.yaml
@@ -0,0 +1,39 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+title: Memblock reserved memory
+
+maintainers:
+  - Mike Rapoport <rppt@...nel.org>
+
+description: |
+  Memblock can serialize its current memory reservations created with
+  reserve_mem command line option across kexec through KHO.
+  The post-KHO kernel can then consume these reservations and they are
+  guaranteed to have the same physical address.
+
+properties:
+  compatible:
+    enum:
+      - reserve-mem-v1
+
+patternProperties:
+  "$[0-9a-f_]+^":
+    $ref: reserve-mem.yaml#
+    description: reserved memory regions
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    memblock {
+      compatible = "memblock-v1";
+      n1 {
+        compatible = "reserve-mem-v1";
+        start = <0xc06b 0x4000000>;
+        size = <0x04 0x00>;
+      };
+    };
diff --git a/Documentation/core-api/kho/bindings/memblock/reserve-mem.yaml b/Documentation/core-api/kho/bindings/memblock/reserve-mem.yaml
new file mode 100644
index 0000000000000..10282d3d1bcdc
--- /dev/null
+++ b/Documentation/core-api/kho/bindings/memblock/reserve-mem.yaml
@@ -0,0 +1,40 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+title: Memblock reserved memory regions
+
+maintainers:
+  - Mike Rapoport <rppt@...nel.org>
+
+description: |
+  Memblock can serialize its current memory reservations created with
+  reserve_mem command line option across kexec through KHO.
+  This object describes each such region.
+
+properties:
+  compatible:
+    enum:
+      - reserve-mem-v1
+
+  start:
+    description: |
+      physical address (u64) of the reserved memory region.
+
+  size:
+    description: |
+      size (u64) of the reserved memory region.
+
+required:
+  - compatible
+  - start
+  - size
+
+additionalProperties: false
+
+examples:
+  - |
+    n1 {
+      compatible = "reserve-mem-v1";
+      start = <0xc06b 0x4000000>;
+      size = <0x04 0x00>;
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index b3be800e5ea46..60e4093042e1b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15425,6 +15425,7 @@ M:	Mike Rapoport <rppt@...nel.org>
 L:	linux-mm@...ck.org
 S:	Maintained
 F:	Documentation/core-api/boot-time-mm.rst
+F:	Documentation/core-api/kho/bindings/memblock/*
 F:	include/linux/memblock.h
 F:	mm/memblock.c
 F:	mm/mm_init.c
-- 
2.49.0.604.gff1f9ca942-goog