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.

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 ("boot1" and "boot2") for special usage
of boot operation where normally is stored the bootloader or boot info.
New JEDEC version also supports up to 4 GP partition for other usage
called "gp1", "gp2", "gp3", "gp4".

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20241002221306.4403-7-ansuelsmth@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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, the 2 BOOT partition (boot1/2) and the 4 GP (gp1/2/3/4) if supported
+  by the eMMC.
+
 properties:
   compatible:
     const: mmc-card
@@ -26,6 +30,24 @@ properties:
       Use this to indicate that the mmc-card has a broken hpi
       implementation, and that hpi should not be used.
 
+patternProperties:
+  "^partitions(-boot[12]|-gp[14])?$":
+    $ref: /schemas/mtd/partitions/partitions.yaml
+
+    patternProperties:
+      "^partition@[0-9a-f]+$":
+        $ref: /schemas/mtd/partitions/partition.yaml
+
+        properties:
+          reg:
+            description: Must be multiple of 512 as it's converted
+              internally from bytes to SECTOR_SIZE (512 bytes)
+
+        required:
+          - reg
+
+        unevaluatedProperties: false
+
 required:
   - compatible
   - reg
@@ -42,6 +64,36 @@ examples:
             compatible = "mmc-card";
             reg = <0>;
             broken-hpi;
+
+            partitions {
+                compatible = "fixed-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-boot1 {
+                compatible = "fixed-partitions";
+
+                #address-cells = <1>;
+                #size-cells = <1>;
+
+                partition@0 {
+                    label = "bl";
+                    reg = <0x0 0x2000000>; /* 32MB */
+                    read-only;
+                };
+            };
         };
     };