[PATCH v15 0/3] mtd: Add support for stacked memories

[PATCH v15 0/3] mtd: Add support for stacked memories

[Luca Ceresoli]

[TL;DR for v15: as agreed with Amit I'm sending a new iteration of his
patches to fix the build-time failure due to a module dependency
loop. Original cover follows.]

This patch series adds stacked support by enhancing the existing mtd-concat 
driver to be more generic.

As background, a few years ago, Bernhard Frauendienst initiated an effort 
[2] to achieve the same, which was later adapted by Miquel [1] to introduce 
stacked mode support. In this approach, partitions to be concatenated were 
specified using a DT property "part-concat" within the partitions 
definition, allowing two MTD devices to function as a single larger one in 
order to be able to define partitions across chip boundaries. However, the 
bindings were not accepted. As a result, the mtd-concat approach was 
dropped, and alternative DT bindings were introduced [3][4][5], describing 
the two flash devices as one. Corresponding SPI core changes to support 
these bindings were later added [6].

While integrating stacked mode support into SPI-NOR, Tudor provided 
additional feedback, leading to discussions about updating the existing 
DT bindings. To address this, I sent an RFC [7] to initiate discussions on 
adapting the DT bindings as suggested by Miquel in [1]. Following that, 
I am now submitting this patch series that updates the virtual concat DT
bindings and the driver referenced in [1], along with some minor mtdcore 
changes. 
Since I have taken ownership of this effort, I have included Bernhard and 
Miquel under the "Suggested-by" tag.

[1] https://lore.kernel.org/linux-mtd/20191127105522.31445-1-miquel.raynal@bootlin.com/
[2] https://lwn.net/ml/linux-kernel/20180907173515.19990-1-kernel@nospam.obeliks.de/
[3] https://github.com/torvalds/linux/commit/f89504300e94524d5d5846ff8b728592ac72cec4
[4] https://github.com/torvalds/linux/commit/eba5368503b4291db7819512600fa014ea17c5a8
[5] https://github.com/torvalds/linux/commit/e2edd1b64f1c79e8abda365149ed62a2a9a494b4
[6]https://github.com/torvalds/linux/commit/4d8ff6b0991d5e86b17b235fc46ec62e9195cb9b
[7] https://lore.kernel.org/all/20241026075347.580858-1-amit.kumar-mahapatra@amd.com/

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
BRANCH: spi-nor/next

Changes in v15:
 - Make mtd_virt_concat built into the mtd module, not a separate
   module. This fixes the build failure [8] caused by the interdependency
   of virt_concat and mtdcore. Keep VIRT_CONCAT an optional feature though.
   [8] https://lore.kernel.org/all/874it99f9i.fsf@bootlin.com/
 - Remove 'default n' line from Kconfig
 - Link to v14: https://lore.kernel.org/linux-mtd/20250623105445.2394825-1-amit.kumar-mahapatra@amd.com/

Changes in v14:
 - Updated 1/3 to address review comments.
 - Updated 3/3 to add mtd_virt_concat_destroy() API that would remove a concat
   incase one of the mtd device, which is part of the concat, is removed.
 
Changes in v13:
 - Updated 1/3 to modify the Device Tree binding to support multiple concatenated devices.
 - Added Rob's "Suggested-by" tag in 1/3.
 - Updated 3/3 to define CONFIG_MTD_VIRT_CONCAT as a boolean and depended on CONFIG_MTD_PARTITIONED_MASTER.
 - Updated 3/3 to remove late_initcall and invoke the API directly from mtdcore instead.
 - Updated 3/3 to add support for concatenating more than two MTD partitions.
 - Updated 3/3 to add support for multiple sets of concatenated devices.

Changes in v12:
 - Add stacked mode support throught mtd-concat driver.

Changes in v11:
- Rebased patch series on top of latest for-next branch.
- Added a new patch(1/10) to replace spi->chip_select with
  spi_get_chipselect() call in tps6594-spi.c.
- Added a new patch(2/10) to replace spi->chip_select with
  spi_get_chipseletc() call in cs35l56_hda_spi.c.
- In spi.c initialized unused CS[] to 0xff and spi->cs_index_mask
  to 0x01 in all flows.
- Updated spi_dev_check() to compare the CS of old spi device with
  the new spi device CS.
- Updated cover letter description to add information regarding GPIO CS
  testing and added Stefen's Tested-by tag in 3/10 patch.

Changes in v10:
 - Rebased patch series on top of latest for-next branch and fixed
   merge conflicts.

Changes in v9:
- Updated 1/8 patch description to add an high-level overview of
  parallel(multi-cs) & stacked design.
- Initialized all unused CS to 0xFF.
- Moved CS check from spi_add_device() to __spi_add_device().
- Updated __spi_add_device() to check to make sure that multiple logical CS
  don't map to the same physical CS and same physical CS doesn't map to
  different logical CS.
- Updated 1/8, 5/8 & 7/8 to support arbitrary number of flash devices
  connected in parallel or stacked mode.
- Updated documentation for chip_select.
- Added a new spi-nor structure member nor->num_flash to keep track of the
  number of flashes connected.
- Added a new patch in the series 4/8 to move write_enable call just before
  spi_mem ops call in SPI-NOR.
- Added comments in SPI core & SPI-NOR.
- Rebased the patch series on top of the latest for-next branch.

Changes in v8:
- Updated __spi_add_device() and spi_set_cs() to fix spi driver failure
  with GPIO CS.
- Rebased the patch series on top of latest for-next branch and fixed
  merge conflicts.
- Updated cover letter description to add information regarding GPIO CS
  testing and request Stefan to provide his Tested-by tag for 1/7 patch.
- Updated 1/7 patch description.

Changes in v7:
- Updated spi_dev_check() to avoid failures for spi driver GPIO CS and
  moved the error message from __spi_add_device() to spi_dev_check().
- Resolved code indentation issue in spi_set_cs().
- In spi_set_cs() call spi_delay_exec( ) once if the controller supports
  multi cs with both the CS backed by GPIO.
- Updated __spi_validate()to add checks for both the GPIO CS.
- Replaced cs_index_mask bit mask with SPI_CS_CNT_MAX.
- Updated struct spi_controller to represent multi CS capability of the
  spi controller through a flag bit SPI_CONTROLLER_MULTI_CS instead of
  a boolen structure member "multi_cs_cap".
- Updated 1/7 patch description .

Changes in v6:
- Rebased on top of latest v6.3-rc1 and fixed merge conflicts in
  spi-mpc512x-psc.c, sfdp.c, spansion.c files and removed spi-omap-100k.c.
- Updated spi_dev_check( ) to reject new devices if any one of the
  chipselect is used by another device.

Changes in v5:
- Rebased the patches on top of v6.3-rc1 and fixed the merge conflicts.
- Fixed compilation warnings in spi-sh-msiof.c with shmobile_defconfig

Changes in v4:
- Fixed build error in spi-pl022.c file - reported by Mark.
- Fixed build error in spi-sn-f-ospi.c file.
- Added Reviewed-by: Serge Semin <fancer.lancer@gmail.com> tag.
- Added two more patches to replace spi->chip_select with API calls in
  mpc832x_rdb.c & cs35l41_hda_spi.c files.

Changes in v3:
- Rebased the patches on top of
  https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next
- Added a patch to convert spi_nor_otp_region_len(nor) &
  spi_nor_otp_n_regions(nor) macros into inline functions
- Added Reviewed-by & Acked-by tags

Changes in v2:
- Rebased the patches on top of v6.2-rc1
- Created separate patch to add get & set APIs for spi->chip_select &
  spi->cs_gpiod, and replaced all spi->chip_select and spi->cs_gpiod
  references with the API calls.
- Created separate patch to add get & set APIs for nor->params.

---
Amit Kumar Mahapatra (3):
      dt-bindings: mtd: Describe MTD partitions concatenation
      mtd: Move struct mtd_concat definition to header file
      mtd: Add driver for concatenating devices

 .../bindings/mtd/partitions/partition.yaml         |  20 ++
 drivers/mtd/Kconfig                                |   9 +
 drivers/mtd/Makefile                               |   1 +
 drivers/mtd/mtd_virt_concat.c                      | 363 +++++++++++++++++++++
 drivers/mtd/mtdconcat.c                            |  12 -
 drivers/mtd/mtdcore.c                              |  19 ++
 drivers/mtd/mtdpart.c                              |   6 +
 include/linux/mtd/concat.h                         |  63 +++-
 8 files changed, 480 insertions(+), 13 deletions(-)
---
base-commit: 5a74a464797585e09561e8e367b62c8b4c289ba1
change-id: 20260129-mtd-virt-concat-2763c07115db

Best regards,
-- 
Luca Ceresoli <luca.ceresoli@bootlin.com>

[PATCH v15 1/3] dt-bindings: mtd: Describe MTD partitions concatenation

[Luca Ceresoli]

From: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>

The AMD QSPI controller supports an advanced connection modes called
Stacked mode which allow the controller to treat two different flashes
as one storage.

In Stacked connection mode flashes share the same SPI bus, but different CS
line, controller driver asserts the CS of the flash to which it needs to
communicate. Stacked mode is a software abstraction rather than a
controller feature or capability. At any given time, the controller
communicates with one of the two connected flash devices, as determined by
the requested address and data length. If an operation starts on one flash
and ends on the other, the mtd layer needs to split it into two separate
operations and adjust the data length accordingly. For more information on
the modes please feel free to go through the controller flash interface
below [1].

To support stacked mode, the existing MTD concat driver has been extended
to be more generic, enabling multiple sets of MTD partitions to be
virtually concatenated, with each set forming a distinct logical MTD
device.

A new Device Tree property is introduced to facilitate this, containing
phandles of the partitions to be concatenated with the one where the
property is defined. This approach supports multiple sets of concatenated
partitions.

[1] https://docs.amd.com/r/en-US/am011-versal-acap-trm/QSPI-Flash-Device-Interface

Suggested-by: Miquel Raynal <miquel.raynal@bootlin.com>
Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
---
 .../bindings/mtd/partitions/partition.yaml           | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Documentation/devicetree/bindings/mtd/partitions/partition.yaml b/Documentation/devicetree/bindings/mtd/partitions/partition.yaml
index 80d0452a2a33..c9aba6838b3c 100644
--- a/Documentation/devicetree/bindings/mtd/partitions/partition.yaml
+++ b/Documentation/devicetree/bindings/mtd/partitions/partition.yaml
@@ -57,6 +57,15 @@ properties:
       user space from
     type: boolean
 
+  part-concat-next:
+    description: List of phandles to MTD partitions that need be concatenated
+      with the current partition.
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    minItems: 1
+    maxItems: 16
+    items:
+      maxItems: 1
+
   align:
     $ref: /schemas/types.yaml#/definitions/uint32
     minimum: 2
@@ -138,4 +147,15 @@ examples:
             reg = <0x200000 0x100000>;
             align = <0x4000>;
         };
+
+        part0: partition@400000 {
+            part-concat-next = <&part1>;
+            label = "part0_0";
+            reg = <0x400000 0x100000>;
+        };
+
+        part1: partition@800000 {
+            label = "part0_1";
+            reg = <0x800000 0x800000>;
+        };
     };

-- 
2.52.0

[PATCH v15 2/3] mtd: Move struct mtd_concat definition to header file

[Luca Ceresoli]

From: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>

To enable a more generic approach for concatenating MTD devices,
struct mtd_concat should be accessible beyond the mtdconcat driver.
Therefore, the definition is being moved to a header file.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
---
 drivers/mtd/mtdconcat.c    | 12 ------------
 include/linux/mtd/concat.h | 12 ++++++++++++
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
index f56f44aa8625..6f2aaceac669 100644
--- a/drivers/mtd/mtdconcat.c
+++ b/drivers/mtd/mtdconcat.c
@@ -20,18 +20,6 @@
 
 #include <asm/div64.h>
 
-/*
- * Our storage structure:
- * Subdev points to an array of pointers to struct mtd_info objects
- * which is allocated along with this structure
- *
- */
-struct mtd_concat {
-	struct mtd_info mtd;
-	int num_subdev;
-	struct mtd_info **subdev;
-};
-
 /*
  * how to calculate the size required for the above structure,
  * including the pointer array subdev points to:
diff --git a/include/linux/mtd/concat.h b/include/linux/mtd/concat.h
index d6f653e07426..b42d9af87c4e 100644
--- a/include/linux/mtd/concat.h
+++ b/include/linux/mtd/concat.h
@@ -9,6 +9,18 @@
 #define MTD_CONCAT_H
 
 
+/*
+ * Our storage structure:
+ * Subdev points to an array of pointers to struct mtd_info objects
+ * which is allocated along with this structure
+ *
+ */
+struct mtd_concat {
+	struct mtd_info mtd;
+	int num_subdev;
+	struct mtd_info **subdev;
+};
+
 struct mtd_info *mtd_concat_create(
     struct mtd_info *subdev[],  /* subdevices to concatenate */
     int num_devs,               /* number of subdevices      */

-- 
2.52.0

[PATCH v15 3/3] mtd: Add driver for concatenating devices

[Luca Ceresoli]

From: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>

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>

---

Changes in v15:
- Build mdt-concat as part of the mtd module, not a separate module
  because they are interdependent; make the Konfig a bool instead of a
  tristate so it is a opt-in feature
- Remove 'default n' Kconfig line, 'n' is the default anyway
---
 drivers/mtd/Kconfig           |   9 ++
 drivers/mtd/Makefile          |   1 +
 drivers/mtd/mtd_virt_concat.c | 363 ++++++++++++++++++++++++++++++++++++++++++
 drivers/mtd/mtdcore.c         |  19 +++
 drivers/mtd/mtdpart.c         |   6 +
 include/linux/mtd/concat.h    |  51 +++++-
 6 files changed, 448 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
index 796a2eccbef0..0421c6208de7 100644
--- a/drivers/mtd/Kconfig
+++ b/drivers/mtd/Kconfig
@@ -206,6 +206,15 @@ config MTD_PARTITIONED_MASTER
 	  the parent of the partition device be the master device, rather than
 	  what lies behind the master.
 
+config MTD_VIRT_CONCAT
+	bool "Virtual concatenated MTD devices"
+	depends on MTD_PARTITIONED_MASTER
+	help
+	  The driver enables the creation of virtual MTD device by
+	  concatenating multiple physical MTD devices into a single
+	  entity. This allows for the creation of partitions larger than
+	  the individual physical chips, extending across chip boundaries.
+
 source "drivers/mtd/chips/Kconfig"
 
 source "drivers/mtd/maps/Kconfig"
diff --git a/drivers/mtd/Makefile b/drivers/mtd/Makefile
index 593d0593a038..7b6dd53e8150 100644
--- a/drivers/mtd/Makefile
+++ b/drivers/mtd/Makefile
@@ -6,6 +6,7 @@
 # Core functionality.
 obj-$(CONFIG_MTD)		+= mtd.o
 mtd-y				:= mtdcore.o mtdsuper.o mtdconcat.o mtdpart.o mtdchar.o
+mtd-$(CONFIG_MTD_VIRT_CONCAT)	+= mtd_virt_concat.o
 
 obj-y				+= parsers/
 
diff --git a/drivers/mtd/mtd_virt_concat.c b/drivers/mtd/mtd_virt_concat.c
new file mode 100644
index 000000000000..aea88d1c9bc5
--- /dev/null
+++ b/drivers/mtd/mtd_virt_concat.c
@@ -0,0 +1,363 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Virtual concat MTD device driver
+ *
+ * Copyright (C) 2018 Bernhard Frauendienst
+ * Author: Bernhard Frauendienst <kernel@nospam.obeliks.de>
+ */
+
+#include <linux/device.h>
+#include <linux/mtd/mtd.h>
+#include "mtdcore.h"
+#include <linux/mtd/partitions.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/slab.h>
+#include <linux/mtd/concat.h>
+
+#define CONCAT_PROP "part-concat-next"
+#define CONCAT_POSTFIX "concat"
+#define MIN_DEV_PER_CONCAT 1
+
+static LIST_HEAD(concat_node_list);
+
+/**
+ * struct mtd_virt_concat_node - components of a concatenation
+ * @head: List handle
+ * @count: Number of nodes
+ * @nodes: Pointer to the nodes (partitions) to concatenate
+ * @concat: Concatenation container
+ */
+struct mtd_virt_concat_node {
+	struct list_head head;
+	unsigned int count;
+	struct device_node **nodes;
+	struct mtd_concat *concat;
+};
+
+/**
+ * mtd_is_part_concat - Check if the device is already part
+ *                       of a concatenated device
+ * @dev:        pointer to 'device_node'
+ *
+ * Return: true if the device is already part of a concatenation,
+ *         false otherwise.
+ */
+static bool mtd_is_part_concat(struct device_node *dev)
+{
+	struct mtd_virt_concat_node *item;
+	int idx;
+
+	list_for_each_entry(item, &concat_node_list, head) {
+		for (idx = 0; idx < item->count; idx++) {
+			if (item->nodes[idx] == dev)
+				return true;
+		}
+	}
+	return false;
+}
+
+static void mtd_virt_concat_put_mtd_devices(struct mtd_concat *concat)
+{
+	int i;
+
+	for (i = 0; i < concat->num_subdev; i++)
+		put_mtd_device(concat->subdev[i]);
+}
+
+void mtd_virt_concat_destroy_joins(void)
+{
+	struct mtd_virt_concat_node *item, *tmp;
+	struct mtd_info *mtd;
+
+	list_for_each_entry_safe(item, tmp, &concat_node_list, head) {
+		mtd = &item->concat->mtd;
+		if (item->concat) {
+			mtd_device_unregister(mtd);
+			kfree(mtd->name);
+			mtd_concat_destroy(mtd);
+			mtd_virt_concat_put_mtd_devices(item->concat);
+		}
+	}
+}
+
+/**
+ * mtd_virt_concat_destroy - Destroy the concat that includes the mtd object
+ * @mtd:        pointer to 'mtd_info'
+ *
+ * Return: 0 on success, -error otherwise.
+ */
+int mtd_virt_concat_destroy(struct mtd_info *mtd)
+{
+	struct mtd_info *child, *master = mtd_get_master(mtd);
+	struct mtd_virt_concat_node *item, *tmp;
+	struct mtd_concat *concat;
+	int idx, ret = 0;
+	bool is_mtd_found;
+
+	list_for_each_entry_safe(item, tmp, &concat_node_list, head) {
+		is_mtd_found = false;
+
+		/* Find the concat item that hold the mtd device */
+		for (idx = 0; idx < item->count; idx++) {
+			if (item->nodes[idx] == mtd->dev.of_node) {
+				is_mtd_found = true;
+				break;
+			}
+		}
+		if (!is_mtd_found)
+			continue;
+		concat = item->concat;
+
+		/*
+		 * Since this concatenated device is being removed, retrieve
+		 * all MTD devices that are part of it and register them
+		 * individually.
+		 */
+		for (idx = 0; idx < concat->num_subdev; idx++) {
+			child = concat->subdev[idx];
+			if (child->dev.of_node != mtd->dev.of_node) {
+				ret = add_mtd_device(child);
+				if (ret)
+					goto out;
+			}
+		}
+		/* Destroy the concat */
+		if (concat->mtd.name) {
+			del_mtd_device(&concat->mtd);
+			kfree(concat->mtd.name);
+			mtd_concat_destroy(&concat->mtd);
+			mtd_virt_concat_put_mtd_devices(item->concat);
+		}
+
+		for (idx = 0; idx < item->count; idx++)
+			of_node_put(item->nodes[idx]);
+
+		kfree(item->nodes);
+		kfree(item);
+	}
+	return 0;
+out:
+	mutex_lock(&master->master.partitions_lock);
+	list_del(&child->part.node);
+	mutex_unlock(&master->master.partitions_lock);
+	kfree(mtd->name);
+	kfree(mtd);
+
+	return ret;
+}
+
+/**
+ * mtd_virt_concat_create_item - Create a concat item
+ * @parts:        pointer to 'device_node'
+ * @count:        number of mtd devices that make up
+ *                the concatenated device.
+ *
+ * Return: 0 on success, -error otherwise.
+ */
+static int mtd_virt_concat_create_item(struct device_node *parts,
+				       unsigned int count)
+{
+	struct mtd_virt_concat_node *item;
+	struct mtd_concat *concat;
+	int i;
+
+	for (i = 0; i < (count - 1); i++) {
+		if (mtd_is_part_concat(of_parse_phandle(parts, CONCAT_PROP, i)))
+			return 0;
+	}
+
+	item = kzalloc(sizeof(*item), GFP_KERNEL);
+	if (!item)
+		return -ENOMEM;
+
+	item->count = count;
+	item->nodes = kcalloc(count, sizeof(*item->nodes), GFP_KERNEL);
+	if (!item->nodes) {
+		kfree(item);
+		return -ENOMEM;
+	}
+
+	/*
+	 * The partition in which "part-concat-next" property
+	 * is defined is the first device in the list of concat
+	 * devices.
+	 */
+	item->nodes[0] = parts;
+
+	for (i = 1; i < count; i++)
+		item->nodes[i] = of_parse_phandle(parts, CONCAT_PROP, (i - 1));
+
+	concat = kzalloc(sizeof(*concat), GFP_KERNEL);
+	if (!concat) {
+		kfree(item);
+		return -ENOMEM;
+	}
+
+	concat->subdev = kcalloc(count, sizeof(*concat->subdev), GFP_KERNEL);
+	if (!concat->subdev) {
+		kfree(item);
+		kfree(concat);
+		return -ENOMEM;
+	}
+	item->concat = concat;
+
+	list_add_tail(&item->head, &concat_node_list);
+
+	return 0;
+}
+
+void mtd_virt_concat_destroy_items(void)
+{
+	struct mtd_virt_concat_node *item, *temp;
+	int i;
+
+	list_for_each_entry_safe(item, temp, &concat_node_list, head) {
+		for (i = 0; i < item->count; i++)
+			of_node_put(item->nodes[i]);
+
+		kfree(item->nodes);
+		kfree(item);
+	}
+}
+
+/**
+ * mtd_virt_concat_create_add - Add a mtd device to the concat list
+ * @mtd:        pointer to 'mtd_info'
+ *
+ * Return: true on success, false otherwise.
+ */
+bool mtd_virt_concat_add(struct mtd_info *mtd)
+{
+	struct mtd_virt_concat_node *item;
+	struct mtd_concat *concat;
+	int idx;
+
+	list_for_each_entry(item, &concat_node_list, head) {
+		concat = item->concat;
+		for (idx = 0; idx < item->count; idx++) {
+			if (item->nodes[idx] == mtd->dev.of_node) {
+				concat->subdev[concat->num_subdev++] = mtd;
+				return true;
+			}
+		}
+	}
+	return false;
+}
+
+/**
+ * mtd_virt_concat_node_create - List all the concatenations found in DT
+ *
+ * Return: 0 on success, -error otherwise.
+ */
+int mtd_virt_concat_node_create(void)
+{
+	struct device_node *parts = NULL;
+	int ret = 0, count = 0;
+
+	/* List all the concatenations found in DT */
+	do {
+		parts = of_find_node_with_property(parts, CONCAT_PROP);
+		if (!of_device_is_available(parts))
+			continue;
+
+		if (mtd_is_part_concat(parts))
+			continue;
+
+		count = of_count_phandle_with_args(parts, CONCAT_PROP, NULL);
+		if (count < MIN_DEV_PER_CONCAT)
+			continue;
+
+		/*
+		 * The partition in which "part-concat-next" property is defined
+		 * is also part of the concat device, so increament count by 1.
+		 */
+		count++;
+
+		ret = mtd_virt_concat_create_item(parts, count);
+		if (ret) {
+			of_node_put(parts);
+			goto destroy_items;
+		}
+	} while (parts);
+
+	return ret;
+
+destroy_items:
+	mtd_virt_concat_destroy_items();
+
+	return ret;
+}
+
+/**
+ * mtd_virt_concat_create_join - Create and register the concatenated
+ *                                 MTD device.
+ *
+ * Return: 0 on success, -error otherwise.
+ */
+int mtd_virt_concat_create_join(void)
+{
+	struct mtd_virt_concat_node *item;
+	struct mtd_concat *concat;
+	struct mtd_info *mtd;
+	ssize_t name_sz;
+	int ret, idx;
+	char *name;
+
+	list_for_each_entry(item, &concat_node_list, head) {
+		concat = item->concat;
+		/*
+		 * Check if item->count != concat->num_subdev, it indicates
+		 * that the MTD information for all devices included in the
+		 * concatenation are not handy, concat MTD device can't be
+		 * created hence switch to next concat device.
+		 */
+		if (item->count != concat->num_subdev) {
+			continue;
+		} else {
+			/* Calculate the legth of the name of the virtual device */
+			for (idx = 0, name_sz = 0; idx < concat->num_subdev; idx++)
+				name_sz += (strlen(concat->subdev[idx]->name) + 1);
+			name_sz += strlen(CONCAT_POSTFIX);
+			name = kmalloc(name_sz + 1, GFP_KERNEL);
+			if (!name) {
+				mtd_virt_concat_put_mtd_devices(concat);
+				return -ENOMEM;
+			}
+
+			ret = 0;
+			for (idx = 0; idx < concat->num_subdev; idx++) {
+				ret += sprintf((name + ret), "%s-",
+					       concat->subdev[idx]->name);
+			}
+			sprintf((name + ret), CONCAT_POSTFIX);
+
+			if (concat->mtd.name) {
+				ret = memcmp(concat->mtd.name, name, name_sz);
+				if (ret == 0)
+					continue;
+			}
+			mtd = mtd_concat_create(concat->subdev, concat->num_subdev, name);
+			if (!mtd) {
+				kfree(name);
+				return -ENXIO;
+			}
+			concat->mtd = *mtd;
+			/* Arbitrary set the first device as parent */
+			concat->mtd.dev.parent = concat->subdev[0]->dev.parent;
+			concat->mtd.dev = concat->subdev[0]->dev;
+
+			/* Add the mtd device */
+			ret = add_mtd_device(&concat->mtd);
+			if (ret)
+				goto destroy_concat;
+		}
+	}
+
+	return 0;
+
+destroy_concat:
+	mtd_concat_destroy(mtd);
+
+	return ret;
+}
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 64808493b4f5..3760065c4e08 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -34,6 +34,7 @@
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/partitions.h>
+#include <linux/mtd/concat.h>
 
 #include "mtdcore.h"
 
@@ -1120,6 +1121,12 @@ int mtd_device_parse_register(struct mtd_info *mtd, const char * const *types,
 			goto out;
 	}
 
+	if (IS_REACHABLE(CONFIG_MTD_VIRT_CONCAT)) {
+		ret = mtd_virt_concat_node_create();
+		if (ret < 0)
+			goto out;
+	}
+
 	/* Prefer parsed partitions over driver-provided fallback */
 	ret = parse_mtd_partitions(mtd, types, parser_data);
 	if (ret == -EPROBE_DEFER)
@@ -1137,6 +1144,11 @@ int mtd_device_parse_register(struct mtd_info *mtd, const char * const *types,
 	if (ret)
 		goto out;
 
+	if (IS_REACHABLE(CONFIG_MTD_VIRT_CONCAT)) {
+		ret = mtd_virt_concat_create_join();
+		if (ret < 0)
+			goto out;
+	}
 	/*
 	 * FIXME: some drivers unfortunately call this function more than once.
 	 * So we have to check if we've already assigned the reboot notifier.
@@ -1186,6 +1198,11 @@ int mtd_device_unregister(struct mtd_info *master)
 	nvmem_unregister(master->otp_user_nvmem);
 	nvmem_unregister(master->otp_factory_nvmem);
 
+	if (IS_REACHABLE(CONFIG_MTD_VIRT_CONCAT)) {
+		err = mtd_virt_concat_destroy(master);
+		if (err)
+			return err;
+	}
 	err = del_mtd_partitions(master);
 	if (err)
 		return err;
@@ -2621,6 +2638,8 @@ static int __init init_mtd(void)
 
 static void __exit cleanup_mtd(void)
 {
+	mtd_virt_concat_destroy_joins();
+	mtd_virt_concat_destroy_items();
 	debugfs_remove_recursive(dfs_dir_mtd);
 	cleanup_mtdchar();
 	if (proc_mtd)
diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index 2876501a7814..fc4483686242 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -18,6 +18,7 @@
 #include <linux/err.h>
 #include <linux/of.h>
 #include <linux/of_platform.h>
+#include <linux/mtd/concat.h>
 
 #include "mtdcore.h"
 
@@ -409,6 +410,11 @@ int add_mtd_partitions(struct mtd_info *parent,
 			goto err_del_partitions;
 		}
 
+		if (IS_REACHABLE(CONFIG_MTD_VIRT_CONCAT)) {
+			if (mtd_virt_concat_add(child))
+				continue;
+		}
+
 		mutex_lock(&master->master.partitions_lock);
 		list_add_tail(&child->part.node, &parent->partitions);
 		mutex_unlock(&master->master.partitions_lock);
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

-- 
2.52.0

Re: [PATCH v15 0/3] mtd: Add support for stacked memories

[Miquel Raynal]

On Thu, 29 Jan 2026 13:09:26 +0100, Luca Ceresoli wrote:
> [TL;DR for v15: as agreed with Amit I'm sending a new iteration of his
> patches to fix the build-time failure due to a module dependency
> loop. Original cover follows.]
> 
> This patch series adds stacked support by enhancing the existing mtd-concat
> driver to be more generic.
> 
> [...]

Thank you for finally re-sending the series after fixing the robot
warning, I will not wait for merging it because this needs to finally
get in, and it's been over the mailing list for 8 months with just a
Kconfig symbol to fix, so:

Applied to mtd/next, thanks!

[1/3] dt-bindings: mtd: Describe MTD partitions concatenation
      commit: 143555defb058336a223ba434619724b4c6d82b0
[2/3] mtd: Move struct mtd_concat definition to header file
      commit: c82100597f3ce5e366f2bc875e9332b7009f5212
[3/3] mtd: Add driver for concatenating devices
      commit: 285871f1ff3c251cba288e7dd9e373c04149a509

Patche(s) should be available on mtd/linux.git and will be
part of the next PR (provided that no robot complains by then).

Kind regards,
Miquèl

Re: [PATCH v15 0/3] mtd: Add support for stacked memories

[Miquel Raynal]

Hello,

On 29/01/2026 at 20:15:32 +01, Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> On Thu, 29 Jan 2026 13:09:26 +0100, Luca Ceresoli wrote:
>> [TL;DR for v15: as agreed with Amit I'm sending a new iteration of his
>> patches to fix the build-time failure due to a module dependency
>> loop. Original cover follows.]
>> 
>> This patch series adds stacked support by enhancing the existing mtd-concat
>> driver to be more generic.
>> 
>> [...]
>
> Thank you for finally re-sending the series after fixing the robot
> warning, I will not wait for merging it because this needs to finally
> get in, and it's been over the mailing list for 8 months with just a
> Kconfig symbol to fix, so:

Unfortunately, for the third time, this series breaks when robots go
over it (see the oe-kbuild-all@lists.linux.dev ML), so I will drop it
again :-/

Sorry,
Miquèl

Re: [PATCH v15 0/3] mtd: Add support for stacked memories

[Luca Ceresoli]

Hi Miquèl,

On Fri Jan 30, 2026 at 3:32 PM CET, Miquel Raynal wrote:
> Hello,
>
> On 29/01/2026 at 20:15:32 +01, Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
>> On Thu, 29 Jan 2026 13:09:26 +0100, Luca Ceresoli wrote:
>>> [TL;DR for v15: as agreed with Amit I'm sending a new iteration of his
>>> patches to fix the build-time failure due to a module dependency
>>> loop. Original cover follows.]
>>>
>>> This patch series adds stacked support by enhancing the existing mtd-concat
>>> driver to be more generic.
>>>
>>> [...]
>>
>> Thank you for finally re-sending the series after fixing the robot
>> warning, I will not wait for merging it because this needs to finally
>> get in, and it's been over the mailing list for 8 months with just a
>> Kconfig symbol to fix, so:
>
> Unfortunately, for the third time, this series breaks when robots go
> over it (see the oe-kbuild-all@lists.linux.dev ML), so I will drop it
> again :-/

Oh, no!

For the records, here are the reports:

  https://lore.kernel.org/oe-kbuild-all/202601302048.TyA0Uh81-lkp@intel.com/T/#u
  https://lore.kernel.org/oe-kbuild-all/202601302001.mGwPwhGE-lkp@intel.com/T/#u

My bad, I apparently haven't tested with CONFIG_MTD_PARTITIONED_MASTER
disabled on the final code. Sorry about that!

At a quick look I think this is the right fix:

	diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
	index 3760065c4e08..48de269f4514 100644
	--- a/drivers/mtd/mtdcore.c
	+++ b/drivers/mtd/mtdcore.c
	@@ -2638,8 +2638,10 @@ static int __init init_mtd(void)

	 static void __exit cleanup_mtd(void)
	 {
	+	if (IS_REACHABLE(CONFIG_MTD_VIRT_CONCAT)) {
	 		mtd_virt_concat_destroy_joins();
	 		mtd_virt_concat_destroy_items();
	+	}
	 	debugfs_remove_recursive(dfs_dir_mtd);
	 	cleanup_mtdchar();
	 	if (proc_mtd)

It passes my my quick build tests, but I'll wait until next week to double
check and test on hardware before resending.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com