linux-kernel - [RFC PATCH 4/4] dt-bindings: mmc: Document support for partition table in mmc-card

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Message-ID: <20240923105937.4374-5-ansuelsmth@gmail.com>
Date: Mon, 23 Sep 2024 12:59:33 +0200
From: Christian Marangi <ansuelsmth@...il.com>
To: Jens Axboe <axboe@...nel.dk>,
	Jonathan Corbet <corbet@....net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Christian Marangi <ansuelsmth@...il.com>,
	INAGAKI Hiroshi <musashino.open@...il.com>,
	Daniel Golle <daniel@...rotopia.org>,
	Christian Brauner <brauner@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Ming Lei <ming.lei@...hat.com>,
	Li Lingfeng <lilingfeng3@...wei.com>,
	Christian Heusel <christian@...sel.eu>,
	linux-block@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mmc@...r.kernel.org,
	devicetree@...r.kernel.org,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>
Subject: [RFC PATCH 4/4] dt-bindings: mmc: Document support for partition table in mmc-card

Document support for defining a partition table in the mmc-card node.

This is needed if the eMMC doesn't have a partition table written and
the bootloader of the device load data by using absolute offset of the
block device. This is common on embedded device that have eMMC installed
to save space and have non removable block devices.

eMMC provide a generic disk for user data and if supported also provide
one or two additional disk (boot0 and boot1) for special usage of boot
operation where normally is stored the bootloader or boot info.

Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
---
 .../devicetree/bindings/mmc/mmc-card.yaml     | 75 +++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/mmc-card.yaml b/Documentation/devicetree/bindings/mmc/mmc-card.yaml
index fd347126449a..fab9fa5c170a 100644
--- a/Documentation/devicetree/bindings/mmc/mmc-card.yaml
+++ b/Documentation/devicetree/bindings/mmc/mmc-card.yaml
@@ -13,6 +13,10 @@ description: |
   This documents describes the devicetree bindings for a mmc-host controller
   child node describing a mmc-card / an eMMC.
 
+  It's possible to define a fixed partition table for an eMMC for the user
+  partition and one of the 2 boot partition (boot0/boot1) if supported by the
+  eMMC.
+
 properties:
   compatible:
     const: mmc-card
@@ -26,6 +30,48 @@ properties:
       Use this to indicate that the mmc-card has a broken hpi
       implementation, and that hpi should not be used.
 
+  "#address-cells": true
+
+  "#size-cells": true
+
+patternProperties:
+  "^partitions(-boot[01])?$":
+    type: object
+
+    properties:
+      "#address-cells": true
+
+      "#size-cells": true
+
+    patternProperties:
+      "@[0-9a-f]+$":
+        type: object
+
+        properties:
+          reg:
+            description: partition's offset and size within the flash (in sector
+              block, 512byte)
+            maxItems: 1
+
+
+          label:
+            description: The label / name for this partition.
+
+          read-only:
+            description: This parameter, if present, is a hint that this partition
+              should only be mounted read-only. This is usually used for flash
+              partitions containing early-boot firmware images or data which should
+              not be clobbered.
+            type: boolean
+
+        required:
+          - reg
+          - label
+
+        additionalProperties: false
+
+    additionalProperties: false
+
 required:
   - compatible
   - reg
@@ -42,6 +88,35 @@ examples:
             compatible = "mmc-card";
             reg = <0>;
             broken-hpi;
+
+            #address-cells = <0>;
+            #size-cells = <0>;
+
+            partitions {
+                #address-cells = <1>;
+                #size-cells = <1>;
+
+                partition@0 {
+                    label = "kernel"; /* Kernel */
+                    reg = <0x0 0x10000>; /* 32 MB */
+                };
+
+                partition@...0 {
+                    label = "rootfs";
+                    reg = <0x3400 0x200000>; /* 1GB */
+                };
+            };
+
+            partitions-boot0 {
+                #address-cells = <1>;
+                #size-cells = <1>;
+
+                partition@0 {
+                    label = "bl";
+                    reg = <0x0 0x10000>; /* 32MB */
+                    read-only;
+                };
+            };
         };
     };
 
-- 
2.45.2