[RFC PATCH v2 5/5] dt-bindings: mmc: Document support for partition table in mmc-card

Christian Marangi
2024-09-25T21:46:54Z

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.

If an OF partition table is detected, any partition table written in the
eMMC will be ignored and won't be parsed.

eMMC provide a generic disk for user data and if supported (JEDEC 4.4+)
also provide 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@gmail.com>
---
.../devicetree/bindings/mmc/mmc-card.yaml | 57 +++++++++++++++++++
1 file changed, 57 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/mmc-card.yaml b/Documentation/devicetree/bindings/mmc/mmc-card.yaml
index fd347126449a..58b6593a0f60 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 +30,30 @@ properties:
Use this to indicate that the mmc-card has a broken hpi
implementation, and that hpi should not be used.

+ "#address-cells":
+ const: 0
+
+ "#size-cells":
+ const: 0
+
+patternProperties:
+ "^partitions(-boot[01])?$":
+ $ref: /schemas/block/partitions/partitions.yaml
+
+ patternProperties:
+ "^partition@[0-9a-f]+$":
+ $ref: /schemas/block/partitions/partition.yaml
+
+ properties:
+ reg:
+ multipleOf: 512
+
+ required:
+ - reg
+ - label
+
+ unevaluatedProperties: false
+
required:
- compatible
- reg
@@ -42,6 +70,35 @@ 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 0x2000000>; /* 32 MB */
+ };
+
+ partition@2000000 {
+ label = "rootfs";
+ reg = <0x2000000 0x40000000>; /* 1GB */
+ };
+ };
+
+ partitions-boot0 {
+ #address-cells = <1>;
+ #size-cells = <1>;
+
+ partition@0 {
+ label = "bl";
+ reg = <0x0 0x2000000>; /* 32MB */
+ read-only;
+ };
+ };
};
};

--
2.45.2