mtd: Add driver for concatenating devices

Introducing CONFIG_MTD_VIRT_CONCAT to separate the legacy flow from the new
approach, where only the concatenated partition is registered as an MTD
device, while the individual partitions that form it are not registered
independently, as they are typically not required by the user.
CONFIG_MTD_VIRT_CONCAT is a boolean configuration option that depends on
CONFIG_MTD_PARTITIONED_MASTER. When enabled, it allows flash nodes to be
exposed as individual MTD devices along with the other partitions.

The solution focuses on fixed-partitions description only as it depends on
device boundaries. It supports multiple sets of concatenated devices, each
comprising two or more partitions.

    flash@0 {
            reg = <0>;
            partitions {
                    compatible = "fixed-partitions";

                    part0@0 {
                            part-concat-next = <&flash0_part1>;
                            label = "part0_0";
                            reg = <0x0 0x800000>;
                    };

                    flash0_part1: part1@800000 {
                            label = "part0_1";
                            reg = <800000 0x800000>;
                    };

                    part2@1000000 {
                            part-concat-next = <&flash1_part0>;
                            label = "part0_2";
                            reg = <0x800000 0x800000>;
                    };
            };
    };

    flash@1 {
            reg = <1>;
            partitions {
                    compatible = "fixed-partitions";

                    flash1_part0: part1@0 {
                            label = "part1_0";
                            reg = <0x0 0x800000>;
                    };

                    part1@800000 {
                            label = "part1_1";
                            reg = <0x800000 0x800000>;
                    };
            };
    };

The partitions that gets created are

flash@0
part0_0-part0_1-concat
flash@1
part1_1
part0_2-part1_0-concat

Suggested-by: Bernhard Frauendienst <kernel@nospam.obeliks.de>
Suggested-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

1 files changed, 50 insertions, 1 deletions

diff --git a/include/linux/mtd/concat.h b/include/linux/mtd/concat.h
index b42d9af87c4e..2cd9d48958a8 100644
--- a/include/linux/mtd/concat.h
+++ b/include/linux/mtd/concat.h
@@ -28,5 +28,54 @@ struct mtd_info *mtd_concat_create(
 
 void mtd_concat_destroy(struct mtd_info *mtd);
 
-#endif
+/**
+ * mtd_virt_concat_node_create - Create a component for concatenation
+ *
+ * Returns a positive number representing the no. of devices found for
+ * concatenation, or a negative error code.
+ *
+ * List all the devices for concatenations found in DT and create a
+ * component for concatenation.
+ */
+int mtd_virt_concat_node_create(void);
+
+/**
+ * mtd_virt_concat_add - add mtd_info object to the list of subdevices for concatenation
+ * @mtd: pointer to new MTD device info structure
+ *
+ * Returns true if the mtd_info object is added successfully else returns false.
+ *
+ * The mtd_info object is added to the list of subdevices for concatenation.
+ * It returns true if a match is found, and false if all subdevices have
+ * already been added or if the mtd_info object does not match any of the
+ * intended MTD devices.
+ */
+bool mtd_virt_concat_add(struct mtd_info *mtd);
 
+/**
+ * mtd_virt_concat_create_join - Create and register the concatenated MTD device
+ *
+ * Returns 0 on succes, or a negative error code.
+ *
+ * Creates and registers the concatenated MTD device
+ */
+int mtd_virt_concat_create_join(void);
+
+/**
+ * mtd_virt_concat_destroy - Remove the concat that includes a specific mtd device
+ *                           as one of its components.
+ * @mtd: pointer to MTD device info structure.
+ *
+ * Returns 0 on succes, or a negative error code.
+ *
+ * If the mtd_info object is part of a concatenated device, all other MTD devices
+ * within that concat are registered individually. The concatenated device is then
+ * removed, along with its concatenation component.
+ *
+ */
+int mtd_virt_concat_destroy(struct mtd_info *mtd);
+
+void mtd_virt_concat_destroy_joins(void);
+void mtd_virt_concat_destroy_items(void);
+
+#endif