mtd: Add support for Airoha partition scheme

Add Documentation for Airoha fixed-partitions compatibles.

Airoha based SoC declare a dedicated partition at the end of the flash to store calibration and device specific data, in addition to fixed partitions.

The offset of this special partition is not well defined as a custom bad block management driver is used that reserve space at the end of the flash.

This binding allows defining all fixed partitions and marking the last one to detect the correct offset.

Signed-off-by Christian Marangi <[email protected]>

---
 .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml   |  1 +
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +68 -0

new file mode 100644
index 000000000000..a45df51065af
@@ -0,0 +1,80 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC partitioning
+
+description: |
+  Airoha based SoC declare a dedicated partition at the end of the flash to
+  store calibration and device specific data, in addition to fixed partitions.
+
+  The offset of this special partition is not well defined as a custom bad block
+  management driver is used that reserve space at the end of the flash.
+
+  This binding allows defining all fixed partitions and marking the last one to
+  detect the correct offset from the new end of the flash.
+
+maintainers:
+  - Christian Marangi <[email protected]>
+
+select: false
+
+properties:
+  compatible:
+    const: airoha,fixed-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: partition.yaml#
+    properties:
+      compatible:
+        const: airoha,dynamic-art
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "airoha,fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+          label = "bootloader";
+          reg = <0x00000000 0x00080000>;
+        };
+
+        partition@80000 {
+          label = "tclinux";
+          reg = <0x00080000 0x02800000>;
+        };
+
+        partition@2880000 {
+          label = "tclinux_slave";
+          reg = <0x02880000 0x02800000>;
+        };

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 12:13:58 +0200:

Quoted 93 lines

Add Documentation for Airoha fixed-partitions compatibles.

Airoha based SoC declare a dedicated partition at the end of the flash to store calibration and device specific data, in addition to fixed partitions.

The offset of this special partition is not well defined as a custom bad block management driver is used that reserve space at the end of the flash.

This binding allows defining all fixed partitions and marking the last one to detect the correct offset.

Signed-off-by Christian Marangi <[email protected]>

---
 .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml   |  1 +
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +68 -0

new file mode 100644
index 000000000000..a45df51065af
@@ -0,0 +1,80 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC partitioning
+
+description: |
+  Airoha based SoC declare a dedicated partition at the end of the flash to
+  store calibration and device specific data, in addition to fixed partitions.
+
+  The offset of this special partition is not well defined as a custom bad block
+  management driver is used that reserve space at the end of the flash.
+
+  This binding allows defining all fixed partitions and marking the last one to
+  detect the correct offset from the new end of the flash.
+
+maintainers:
+  - Christian Marangi <[email protected]>
+
+select: false
+
+properties:
+  compatible:
+    const: airoha,fixed-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: partition.yaml#
+    properties:
+      compatible:
+        const: airoha,dynamic-art
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "airoha,fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+          label = "bootloader";
+          reg = <0x00000000 0x00080000>;
+        };
+
+        partition@80000 {
+          label = "tclinux";
+          reg = <0x00080000 0x02800000>;
+        };
+
+        partition@2880000 {
+          label = "tclinux_slave";
+          reg = <0x02880000 0x02800000>;
+        };

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml line 78

Quoted 10 lines

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +10 -0

+
+        partition@5080000 {
+          label = "rootfs_data";
+          reg = <0x5080000 0x00800000>;
+        };
+
+        partition@ffffffff {
+          compatible = "airoha,dynamic-art";
+          label = "art";
+          reg = <0xffffffff 0x00300000>;

I'm a little bit puzzled by this kind of information which is known to be wrong. As the partition offset and size must be dynamically calculated, this reg property (as well as the size parameter of the previous one) are notably wrong. I guess we are not fully constrained by the fixed-partitions schema here, so could we avoid the reg property in the airoha,dynamic-art partition? Maybe we also need a #define for a specific placeholder in the penultimate reg property too (for the size).

Quoted 108 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 12:13:58 +0200:

Quoted 93 lines

Add Documentation for Airoha fixed-partitions compatibles.

Airoha based SoC declare a dedicated partition at the end of the flash to store calibration and device specific data, in addition to fixed partitions.

The offset of this special partition is not well defined as a custom bad block management driver is used that reserve space at the end of the flash.

This binding allows defining all fixed partitions and marking the last one to detect the correct offset.

Signed-off-by Christian Marangi <[email protected]>

---
 .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml   |  1 +
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +68 -0

new file mode 100644
index 000000000000..a45df51065af
@@ -0,0 +1,80 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC partitioning
+
+description: |
+  Airoha based SoC declare a dedicated partition at the end of the flash to
+  store calibration and device specific data, in addition to fixed partitions.
+
+  The offset of this special partition is not well defined as a custom bad block
+  management driver is used that reserve space at the end of the flash.
+
+  This binding allows defining all fixed partitions and marking the last one to
+  detect the correct offset from the new end of the flash.
+
+maintainers:
+  - Christian Marangi <[email protected]>
+
+select: false
+
+properties:
+  compatible:
+    const: airoha,fixed-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: partition.yaml#
+    properties:
+      compatible:
+        const: airoha,dynamic-art
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "airoha,fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+          label = "bootloader";
+          reg = <0x00000000 0x00080000>;
+        };
+
+        partition@80000 {
+          label = "tclinux";
+          reg = <0x00080000 0x02800000>;
+        };
+
+        partition@2880000 {
+          label = "tclinux_slave";
+          reg = <0x02880000 0x02800000>;
+        };

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml line 78

Quoted 10 lines

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +10 -0

+
+        partition@5080000 {
+          label = "rootfs_data";
+          reg = <0x5080000 0x00800000>;
+        };
+
+        partition@ffffffff {
+          compatible = "airoha,dynamic-art";
+          label = "art";
+          reg = <0xffffffff 0x00300000>;  

Quoted 8 lines

I'm a little bit puzzled by this kind of information which is known to be wrong. As the partition offset and size must be dynamically calculated, this reg property (as well as the size parameter of the previous one) are notably wrong. I guess we are not fully constrained by the fixed-partitions schema here, so could we avoid the reg property in the airoha,dynamic-art partition? Maybe we also need a #define for a specific placeholder in the penultimate reg property too (for the size).

Maybe instead of reg we can use a property like size?

Can you better elaborate the suggestion about the #define?

Do you mean for case where the last partition might overlap with the penultimate? Honestly in such case I would error hard, that case happen when too much space is reserved and that is a misconfiguration of the system (developer error)

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 13:35:38 +0200:

Quoted 118 lines · Miquel Raynal

Quoted 108 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 12:13:58 +0200:

Quoted 93 lines

Add Documentation for Airoha fixed-partitions compatibles.

Airoha based SoC declare a dedicated partition at the end of the flash to store calibration and device specific data, in addition to fixed partitions.

The offset of this special partition is not well defined as a custom bad block management driver is used that reserve space at the end of the flash.

This binding allows defining all fixed partitions and marking the last one to detect the correct offset.

Signed-off-by Christian Marangi <[email protected]>

---
 .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml   |  1 +
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +68 -0

new file mode 100644
index 000000000000..a45df51065af
@@ -0,0 +1,80 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC partitioning
+
+description: |
+  Airoha based SoC declare a dedicated partition at the end of the flash to
+  store calibration and device specific data, in addition to fixed partitions.
+
+  The offset of this special partition is not well defined as a custom bad block
+  management driver is used that reserve space at the end of the flash.
+
+  This binding allows defining all fixed partitions and marking the last one to
+  detect the correct offset from the new end of the flash.
+
+maintainers:
+  - Christian Marangi <[email protected]>
+
+select: false
+
+properties:
+  compatible:
+    const: airoha,fixed-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: partition.yaml#
+    properties:
+      compatible:
+        const: airoha,dynamic-art
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "airoha,fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+          label = "bootloader";
+          reg = <0x00000000 0x00080000>;
+        };
+
+        partition@80000 {
+          label = "tclinux";
+          reg = <0x00080000 0x02800000>;
+        };
+
+        partition@2880000 {
+          label = "tclinux_slave";
+          reg = <0x02880000 0x02800000>;
+        };

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml line 78

Quoted 10 lines

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +10 -0

+
+        partition@5080000 {
+          label = "rootfs_data";
+          reg = <0x5080000 0x00800000>;
+        };
+
+        partition@ffffffff {
+          compatible = "airoha,dynamic-art";
+          label = "art";
+          reg = <0xffffffff 0x00300000>;  

Quoted 8 lines

I'm a little bit puzzled by this kind of information which is known to be wrong. As the partition offset and size must be dynamically calculated, this reg property (as well as the size parameter of the previous one) are notably wrong. I guess we are not fully constrained by the fixed-partitions schema here, so could we avoid the reg property in the airoha,dynamic-art partition? Maybe we also need a #define for a specific placeholder in the penultimate reg property too (for the size).

Quoted 8 lines

Maybe instead of reg we can use a property like size?

Can you better elaborate the suggestion about the #define?

Do you mean for case where the last partition might overlap with the penultimate? Honestly in such case I would error hard, that case happen when too much space is reserved and that is a misconfiguration of the system (developer error)

That's not what I mean.

In the above case you say partition "partition@5080000" is 0x800000 bytes long. This is obviously wrong otherwise you would know where the art partition starts. And right after you're saying partition "partition@ffffffff" starts at 0xffffffff and is 0x300000 bytes long. This is also wrong because 0xffffffff is not a valid start address and IIUC 0x300000 is also unknown and dynamically derived.

So for the art partition my advise if you know nothing about the start/length is to just skip the reg property. For the previous partition I'd maybe use a definition (whose name is to discuss) instead of the wrong size argument (the start offset being correct on his side).

Quoted 140 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 13:35:38 +0200:

Quoted 118 lines · Miquel Raynal

Quoted 108 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 12:13:58 +0200:

Quoted 93 lines

Add Documentation for Airoha fixed-partitions compatibles.

Airoha based SoC declare a dedicated partition at the end of the flash to store calibration and device specific data, in addition to fixed partitions.

The offset of this special partition is not well defined as a custom bad block management driver is used that reserve space at the end of the flash.

This binding allows defining all fixed partitions and marking the last one to detect the correct offset.

Signed-off-by Christian Marangi <[email protected]>

---
 .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml   |  1 +
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +68 -0

new file mode 100644
index 000000000000..a45df51065af
@@ -0,0 +1,80 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC partitioning
+
+description: |
+  Airoha based SoC declare a dedicated partition at the end of the flash to
+  store calibration and device specific data, in addition to fixed partitions.
+
+  The offset of this special partition is not well defined as a custom bad block
+  management driver is used that reserve space at the end of the flash.
+
+  This binding allows defining all fixed partitions and marking the last one to
+  detect the correct offset from the new end of the flash.
+
+maintainers:
+  - Christian Marangi <[email protected]>
+
+select: false
+
+properties:
+  compatible:
+    const: airoha,fixed-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: partition.yaml#
+    properties:
+      compatible:
+        const: airoha,dynamic-art
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "airoha,fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+          label = "bootloader";
+          reg = <0x00000000 0x00080000>;
+        };
+
+        partition@80000 {
+          label = "tclinux";
+          reg = <0x00080000 0x02800000>;
+        };
+
+        partition@2880000 {
+          label = "tclinux_slave";
+          reg = <0x02880000 0x02800000>;
+        };

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml line 78

Quoted 10 lines

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +10 -0

+
+        partition@5080000 {
+          label = "rootfs_data";
+          reg = <0x5080000 0x00800000>;
+        };
+
+        partition@ffffffff {
+          compatible = "airoha,dynamic-art";
+          label = "art";
+          reg = <0xffffffff 0x00300000>;    

Quoted 8 lines

I'm a little bit puzzled by this kind of information which is known to be wrong. As the partition offset and size must be dynamically calculated, this reg property (as well as the size parameter of the previous one) are notably wrong. I guess we are not fully constrained by the fixed-partitions schema here, so could we avoid the reg property in the airoha,dynamic-art partition? Maybe we also need a #define for a specific placeholder in the penultimate reg property too (for the size).

Quoted 8 lines

Maybe instead of reg we can use a property like size?

Can you better elaborate the suggestion about the #define?

Do you mean for case where the last partition might overlap with the penultimate? Honestly in such case I would error hard, that case happen when too much space is reserved and that is a misconfiguration of the system (developer error)

That's not what I mean.

In the above case you say partition "partition@5080000" is 0x800000 bytes long. This is obviously wrong otherwise you would know where the art partition starts. And right after you're saying partition "partition@ffffffff" starts at 0xffffffff and is 0x300000 bytes long. This is also wrong because 0xffffffff is not a valid start address and IIUC 0x300000 is also unknown and dynamically derived.

Quoted 5 lines

So for the art partition my advise if you know nothing about the start/length is to just skip the reg property. For the previous partition I'd maybe use a definition (whose name is to discuss) instead of the wrong size argument (the start offset being correct on his side).

Ok probably the description isn't clear enough. The missing info that require this parser is the flash end.

Following the example we know the size of rootfs_data and start offset AND we know the size of the ART partition.

There might be a space in the middle unused between the rootfs_data partition and the art partition. What is derived is the starting offset of the art partition that is flash end - art partition size. (where flash end change and is not always the same due to how the special bad block managament table reserved space is handled)

This is why 0xffffffff, used as a dummy offset to signal it will be parsed at runtime. On second tought tho maybe using this dummy offset is wrong and I should just have something like

length = <0x300000>;

Is it clear now? Sorry for any confusion.

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 14:06:11 +0200:

Quoted 163 lines · Miquel Raynal

Quoted 140 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 13:35:38 +0200:

Quoted 118 lines · Miquel Raynal

Quoted 108 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 12:13:58 +0200:

Quoted 93 lines

Add Documentation for Airoha fixed-partitions compatibles.

Airoha based SoC declare a dedicated partition at the end of the flash to store calibration and device specific data, in addition to fixed partitions.

The offset of this special partition is not well defined as a custom bad block management driver is used that reserve space at the end of the flash.

This binding allows defining all fixed partitions and marking the last one to detect the correct offset.

Signed-off-by Christian Marangi <[email protected]>

---
 .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml   |  1 +
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +68 -0

new file mode 100644
index 000000000000..a45df51065af
@@ -0,0 +1,80 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC partitioning
+
+description: |
+  Airoha based SoC declare a dedicated partition at the end of the flash to
+  store calibration and device specific data, in addition to fixed partitions.
+
+  The offset of this special partition is not well defined as a custom bad block
+  management driver is used that reserve space at the end of the flash.
+
+  This binding allows defining all fixed partitions and marking the last one to
+  detect the correct offset from the new end of the flash.
+
+maintainers:
+  - Christian Marangi <[email protected]>
+
+select: false
+
+properties:
+  compatible:
+    const: airoha,fixed-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: partition.yaml#
+    properties:
+      compatible:
+        const: airoha,dynamic-art
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "airoha,fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+          label = "bootloader";
+          reg = <0x00000000 0x00080000>;
+        };
+
+        partition@80000 {
+          label = "tclinux";
+          reg = <0x00080000 0x02800000>;
+        };
+
+        partition@2880000 {
+          label = "tclinux_slave";
+          reg = <0x02880000 0x02800000>;
+        };

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml line 78

Quoted 10 lines

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +10 -0

+
+        partition@5080000 {
+          label = "rootfs_data";
+          reg = <0x5080000 0x00800000>;
+        };
+
+        partition@ffffffff {
+          compatible = "airoha,dynamic-art";
+          label = "art";
+          reg = <0xffffffff 0x00300000>;    

Quoted 8 lines

I'm a little bit puzzled by this kind of information which is known to be wrong. As the partition offset and size must be dynamically calculated, this reg property (as well as the size parameter of the previous one) are notably wrong. I guess we are not fully constrained by the fixed-partitions schema here, so could we avoid the reg property in the airoha,dynamic-art partition? Maybe we also need a #define for a specific placeholder in the penultimate reg property too (for the size).

Quoted 8 lines

Maybe instead of reg we can use a property like size?

Can you better elaborate the suggestion about the #define?

Do you mean for case where the last partition might overlap with the penultimate? Honestly in such case I would error hard, that case happen when too much space is reserved and that is a misconfiguration of the system (developer error)

That's not what I mean.

In the above case you say partition "partition@5080000" is 0x800000 bytes long. This is obviously wrong otherwise you would know where the art partition starts. And right after you're saying partition "partition@ffffffff" starts at 0xffffffff and is 0x300000 bytes long. This is also wrong because 0xffffffff is not a valid start address and IIUC 0x300000 is also unknown and dynamically derived.

Quoted 5 lines

So for the art partition my advise if you know nothing about the start/length is to just skip the reg property. For the previous partition I'd maybe use a definition (whose name is to discuss) instead of the wrong size argument (the start offset being correct on his side).

Ok probably the description isn't clear enough. The missing info that require this parser is the flash end.

Following the example we know the size of rootfs_data and start offset AND we know the size of the ART partition.

There might be a space in the middle unused between the rootfs_data partition and the art partition. What is derived is the starting offset of the art partition that is flash end - art partition size. (where flash end change and is not always the same due to how the special bad block managament table reserved space is handled)

This is why 0xffffffff, used as a dummy offset to signal it will be parsed at runtime. On second tought tho maybe using this dummy offset is wrong and I should just have something like

Quoted 3 lines

length = <0x300000>;

Is it clear now? Sorry for any confusion.

I'm sorry but not really. You know the end of the physical device and the size of the ART partition, so you must know its start as well?

Quoted 167 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 14:06:11 +0200:

Quoted 163 lines · Miquel Raynal

Quoted 140 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 13:35:38 +0200:

Quoted 118 lines · Miquel Raynal

Quoted 108 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 12:13:58 +0200:

Quoted 93 lines

Add Documentation for Airoha fixed-partitions compatibles.

Airoha based SoC declare a dedicated partition at the end of the flash to store calibration and device specific data, in addition to fixed partitions.

The offset of this special partition is not well defined as a custom bad block management driver is used that reserve space at the end of the flash.

This binding allows defining all fixed partitions and marking the last one to detect the correct offset.

Signed-off-by Christian Marangi <[email protected]>

---
 .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml   |  1 +
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +68 -0

new file mode 100644
index 000000000000..a45df51065af
@@ -0,0 +1,80 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC partitioning
+
+description: |
+  Airoha based SoC declare a dedicated partition at the end of the flash to
+  store calibration and device specific data, in addition to fixed partitions.
+
+  The offset of this special partition is not well defined as a custom bad block
+  management driver is used that reserve space at the end of the flash.
+
+  This binding allows defining all fixed partitions and marking the last one to
+  detect the correct offset from the new end of the flash.
+
+maintainers:
+  - Christian Marangi <[email protected]>
+
+select: false
+
+properties:
+  compatible:
+    const: airoha,fixed-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: partition.yaml#
+    properties:
+      compatible:
+        const: airoha,dynamic-art
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "airoha,fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+          label = "bootloader";
+          reg = <0x00000000 0x00080000>;
+        };
+
+        partition@80000 {
+          label = "tclinux";
+          reg = <0x00080000 0x02800000>;
+        };
+
+        partition@2880000 {
+          label = "tclinux_slave";
+          reg = <0x02880000 0x02800000>;
+        };

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml line 78

Quoted 10 lines

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +10 -0

+
+        partition@5080000 {
+          label = "rootfs_data";
+          reg = <0x5080000 0x00800000>;
+        };
+
+        partition@ffffffff {
+          compatible = "airoha,dynamic-art";
+          label = "art";
+          reg = <0xffffffff 0x00300000>;      

Quoted 8 lines

I'm a little bit puzzled by this kind of information which is known to be wrong. As the partition offset and size must be dynamically calculated, this reg property (as well as the size parameter of the previous one) are notably wrong. I guess we are not fully constrained by the fixed-partitions schema here, so could we avoid the reg property in the airoha,dynamic-art partition? Maybe we also need a #define for a specific placeholder in the penultimate reg property too (for the size).

Quoted 8 lines

Maybe instead of reg we can use a property like size?

Can you better elaborate the suggestion about the #define?

Do you mean for case where the last partition might overlap with the penultimate? Honestly in such case I would error hard, that case happen when too much space is reserved and that is a misconfiguration of the system (developer error)

That's not what I mean.

In the above case you say partition "partition@5080000" is 0x800000 bytes long. This is obviously wrong otherwise you would know where the art partition starts. And right after you're saying partition "partition@ffffffff" starts at 0xffffffff and is 0x300000 bytes long. This is also wrong because 0xffffffff is not a valid start address and IIUC 0x300000 is also unknown and dynamically derived.

Quoted 5 lines

So for the art partition my advise if you know nothing about the start/length is to just skip the reg property. For the previous partition I'd maybe use a definition (whose name is to discuss) instead of the wrong size argument (the start offset being correct on his side).

Ok probably the description isn't clear enough. The missing info that require this parser is the flash end.

Following the example we know the size of rootfs_data and start offset AND we know the size of the ART partition.

There might be a space in the middle unused between the rootfs_data partition and the art partition. What is derived is the starting offset of the art partition that is flash end - art partition size. (where flash end change and is not always the same due to how the special bad block managament table reserved space is handled)

This is why 0xffffffff, used as a dummy offset to signal it will be parsed at runtime. On second tought tho maybe using this dummy offset is wrong and I should just have something like

Quoted 7 lines

Quoted 3 lines

length = <0x300000>;

Is it clear now? Sorry for any confusion.

I'm sorry but not really. You know the end of the physical device and the size of the ART partition, so you must know its start as well?

Before the system boot we know:
- size of the ART partition
- real size of the physical device (512mb... 1G... 64mb...)

When the physical device is probed (nand) a special driver is loaded (before mtd parsing logic) that change the physical size of the device (mtd->size) as at the end of the nand some space is reserved for bad block management and other metadata info.

So on the mtd parsing logic we know:
- size of the ART partitiomn
- new size of the physical device (512-reserved space...)

And we calculate the start offset of the ART partition.

It's very difficult to know what is the new size of the physical device after the driver change it as it might change based on the internal configuration of the driver itself.

Hi Christian,

[email protected] wrote on Mon, 30 Sep 2024 12:10:21 +0200:

Quoted 176 lines · Miquel Raynal

Quoted 167 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 14:06:11 +0200:

Quoted 163 lines · Miquel Raynal

Quoted 140 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 13:35:38 +0200:

Quoted 118 lines · Miquel Raynal

Quoted 108 lines

Hi Christian,

[email protected] wrote on Wed, 25 Sep 2024 12:13:58 +0200:

Quoted 93 lines

Add Documentation for Airoha fixed-partitions compatibles.

Airoha based SoC declare a dedicated partition at the end of the flash to store calibration and device specific data, in addition to fixed partitions.

The offset of this special partition is not well defined as a custom bad block management driver is used that reserve space at the end of the flash.

This binding allows defining all fixed partitions and marking the last one to detect the correct offset.

Signed-off-by Christian Marangi <[email protected]>

---
 .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml   |  1 +
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +68 -0

new file mode 100644
index 000000000000..a45df51065af
@@ -0,0 +1,80 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC partitioning
+
+description: |
+  Airoha based SoC declare a dedicated partition at the end of the flash to
+  store calibration and device specific data, in addition to fixed partitions.
+
+  The offset of this special partition is not well defined as a custom bad block
+  management driver is used that reserve space at the end of the flash.
+
+  This binding allows defining all fixed partitions and marking the last one to
+  detect the correct offset from the new end of the flash.
+
+maintainers:
+  - Christian Marangi <[email protected]>
+
+select: false
+
+properties:
+  compatible:
+    const: airoha,fixed-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: partition.yaml#
+    properties:
+      compatible:
+        const: airoha,dynamic-art
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "airoha,fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+          label = "bootloader";
+          reg = <0x00000000 0x00080000>;
+        };
+
+        partition@80000 {
+          label = "tclinux";
+          reg = <0x00080000 0x02800000>;
+        };
+
+        partition@2880000 {
+          label = "tclinux_slave";
+          reg = <0x02880000 0x02800000>;
+        };

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml line 78

Quoted 10 lines

Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml new file +10 -0

+
+        partition@5080000 {
+          label = "rootfs_data";
+          reg = <0x5080000 0x00800000>;
+        };
+
+        partition@ffffffff {
+          compatible = "airoha,dynamic-art";
+          label = "art";
+          reg = <0xffffffff 0x00300000>;      

Quoted 8 lines

I'm a little bit puzzled by this kind of information which is known to be wrong. As the partition offset and size must be dynamically calculated, this reg property (as well as the size parameter of the previous one) are notably wrong. I guess we are not fully constrained by the fixed-partitions schema here, so could we avoid the reg property in the airoha,dynamic-art partition? Maybe we also need a #define for a specific placeholder in the penultimate reg property too (for the size).

Quoted 8 lines

Maybe instead of reg we can use a property like size?

Can you better elaborate the suggestion about the #define?

Do you mean for case where the last partition might overlap with the penultimate? Honestly in such case I would error hard, that case happen when too much space is reserved and that is a misconfiguration of the system (developer error)

That's not what I mean.

In the above case you say partition "partition@5080000" is 0x800000 bytes long. This is obviously wrong otherwise you would know where the art partition starts. And right after you're saying partition "partition@ffffffff" starts at 0xffffffff and is 0x300000 bytes long. This is also wrong because 0xffffffff is not a valid start address and IIUC 0x300000 is also unknown and dynamically derived.

Quoted 5 lines

So for the art partition my advise if you know nothing about the start/length is to just skip the reg property. For the previous partition I'd maybe use a definition (whose name is to discuss) instead of the wrong size argument (the start offset being correct on his side).

Ok probably the description isn't clear enough. The missing info that require this parser is the flash end.

Following the example we know the size of rootfs_data and start offset AND we know the size of the ART partition.

There might be a space in the middle unused between the rootfs_data partition and the art partition. What is derived is the starting offset of the art partition that is flash end - art partition size. (where flash end change and is not always the same due to how the special bad block managament table reserved space is handled)

This is why 0xffffffff, used as a dummy offset to signal it will be parsed at runtime. On second tought tho maybe using this dummy offset is wrong and I should just have something like

Quoted 7 lines

Quoted 3 lines

length = <0x300000>;

Is it clear now? Sorry for any confusion.

I'm sorry but not really. You know the end of the physical device and the size of the ART partition, so you must know its start as well?

Quoted 8 lines

Before the system boot we know:
- size of the ART partition
- real size of the physical device (512mb... 1G... 64mb...)

When the physical device is probed (nand) a special driver is loaded (before mtd parsing logic) that change the physical size of the device (mtd->size) as at the end of the nand some space is reserved for bad block management and other metadata info.

Here you are explaining what you intend Linux to do, right? I would like to understand what you are trying to solve. I dont understand why you need the size change, I don't understand why you don't know the start of the ART partition, I don't understand what the data you are hiding contains and who uses it :-) I'm sorry, this is too unclear yet.

Quoting your cover letter:

"This require dynamic calculation of the offset as some dedicated driver for bad block management might be used that reserve some space at the end of the flash for bad block accounting. This special driver change the end offset of the flash hence a dynamic parser is needed."

I don't know what this "dedicated driver" is, I don't understand why it is needed.

Quoted 10 lines

So on the mtd parsing logic we know:
- size of the ART partitiomn
- new size of the physical device (512-reserved space...)

And we calculate the start offset of the ART partition.

It's very difficult to know what is the new size of the physical device after the driver change it as it might change based on the internal configuration of the driver itself.

Thanks,
Miquèl

Quoted 33 lines

Quoted 24 lines

Quoted 16 lines

Quoted 16 lines

Ok probably the description isn't clear enough. The missing info that require this parser is the flash end.

Following the example we know the size of rootfs_data and start offset AND we know the size of the ART partition.

There might be a space in the middle unused between the rootfs_data partition and the art partition. What is derived is the starting offset of the art partition that is flash end - art partition size. (where flash end change and is not always the same due to how the special bad block managament table reserved space is handled)

This is why 0xffffffff, used as a dummy offset to signal it will be parsed at runtime. On second tought tho maybe using this dummy offset is wrong and I should just have something like

Quoted 7 lines

Quoted 3 lines

length = <0x300000>;

Is it clear now? Sorry for any confusion.

I'm sorry but not really. You know the end of the physical device and the size of the ART partition, so you must know its start as well?

Quoted 8 lines

Before the system boot we know:
- size of the ART partition
- real size of the physical device (512mb... 1G... 64mb...)

When the physical device is probed (nand) a special driver is loaded (before mtd parsing logic) that change the physical size of the device (mtd->size) as at the end of the nand some space is reserved for bad block management and other metadata info.

Quoted 5 lines

Here you are explaining what you intend Linux to do, right? I would like to understand what you are trying to solve. I dont understand why you need the size change, I don't understand why you don't know the start of the ART partition, I don't understand what the data you are hiding contains and who uses it :-) I'm sorry, this is too unclear yet.

Totally not a problem and thanks a lot for you keep asking them... More than happy to clear things, I'm trying to solve a problem present on Airoha SoC and upstreaming a correct parser for it.

What I'm trying to solve:

Correct access to this partition at the end of the flash in an automated way.

The content of this partition is the usual ART partition found on lots of embedded devices. MAC address, wifi calibration data, serial. Usage is NVMEM cells and userspace with dd command to extract data from.

Airoha use something also used by some mediatek SoC. They call it BMT and it's currently used downstream in OpenWrt and they firmware. This is also used in the bootloader.

The usage of BMT is a custom way to handle bad blocks entirely by software. At the end of the flash some space is reserved where info about all the blocks of the flash are put. I'm not 100% sure about the functionality of this but it can relocate block and do magic things to handle bad blocks. For the scope of this change, the important info is that after the BMT is probed, the operation of "reserving space" is done by reducing the MTD flash size. So from the MTD subsystem, it does see a smaller flash than it actually is.

The reserved space change! Across SoC or even devices but the BMT is a must where it's used as bootloader makes use of it and writing to it might confuse the bootloader corrupting data. (one block might be flagged as bad ad data moved, BMT driver validates his table and do operation)

Hi Christian,

Quoted 65 lines

Quoted 33 lines

Quoted 24 lines

Quoted 16 lines

Quoted 16 lines

Ok probably the description isn't clear enough. The missing info that require this parser is the flash end.

Following the example we know the size of rootfs_data and start offset AND we know the size of the ART partition.

There might be a space in the middle unused between the rootfs_data partition and the art partition. What is derived is the starting offset of the art partition that is flash end - art partition size. (where flash end change and is not always the same due to how the special bad block managament table reserved space is handled)

This is why 0xffffffff, used as a dummy offset to signal it will be parsed at runtime. On second tought tho maybe using this dummy offset is wrong and I should just have something like

Quoted 7 lines

Quoted 3 lines

length = <0x300000>;

Is it clear now? Sorry for any confusion.

I'm sorry but not really. You know the end of the physical device and the size of the ART partition, so you must know its start as well?

Quoted 8 lines

Before the system boot we know:
- size of the ART partition
- real size of the physical device (512mb... 1G... 64mb...)

When the physical device is probed (nand) a special driver is loaded (before mtd parsing logic) that change the physical size of the device (mtd->size) as at the end of the nand some space is reserved for bad block management and other metadata info.

Quoted 5 lines

Here you are explaining what you intend Linux to do, right? I would like to understand what you are trying to solve. I dont understand why you need the size change, I don't understand why you don't know the start of the ART partition, I don't understand what the data you are hiding contains and who uses it :-) I'm sorry, this is too unclear yet.

Totally not a problem and thanks a lot for you keep asking them... More than happy to clear things, I'm trying to solve a problem present on Airoha SoC and upstreaming a correct parser for it.

What I'm trying to solve:

Correct access to this partition at the end of the flash in an automated way.

The content of this partition is the usual ART partition found on lots of embedded devices. MAC address, wifi calibration data, serial. Usage is NVMEM cells and userspace with dd command to extract data from.

Airoha use something also used by some mediatek SoC. They call it BMT and it's currently used downstream in OpenWrt and they firmware. This is also used in the bootloader.

The usage of BMT is a custom way to handle bad blocks entirely by software. At the end of the flash some space is reserved where info about all the blocks of the flash are put. I'm not 100% sure about the functionality of this but it can relocate block and do magic things to handle bad blocks. For the scope of this change, the important info is that after the BMT is probed, the operation of "reserving space" is done by reducing the MTD flash size. So from the MTD subsystem, it does see a smaller flash than it actually is.

Quoted 5 lines

The reserved space change! Across SoC or even devices but the BMT is a must where it's used as bootloader makes use of it and writing to it might confuse the bootloader corrupting data. (one block might be flagged as bad ad data moved, BMT driver validates his table and do operation)

Ok, I think that's way clearer now.

So the BMT driver does not exist in mainline Linux, but you would like to skip this part of the MTD device to avoid smashing it. And it is in use by the vendor Bootloader I guess?

Is it some kind of table that is written by the chip itself in order to maintain a list of auto-replacement blocks for bad blocks? Can the size of this table move with the use of the device? (if yes, it's problematic, we don't want to resize MTD partitions without noticing, it would break eg. UBI).

I believe this BMT block is going against the bad block handling in Linux, so I really wonder how one can use both mechanisms in a system. If the BMT layer takes "one random block" to map a corrupted one on it, it totally defeats the current bad block model we have in MTD/UBI and simply cannot be supported at all. Just skipping the currently-used-for-BMT blocks sounds like a very bad idea that will break your system, later.

Quoted 67 lines

Hi Christian,

Quoted 65 lines

Quoted 33 lines

Quoted 24 lines

Quoted 16 lines

Quoted 16 lines

Ok probably the description isn't clear enough. The missing info that require this parser is the flash end.

Following the example we know the size of rootfs_data and start offset AND we know the size of the ART partition.

There might be a space in the middle unused between the rootfs_data partition and the art partition. What is derived is the starting offset of the art partition that is flash end - art partition size. (where flash end change and is not always the same due to how the special bad block managament table reserved space is handled)

This is why 0xffffffff, used as a dummy offset to signal it will be parsed at runtime. On second tought tho maybe using this dummy offset is wrong and I should just have something like

Quoted 7 lines

Quoted 3 lines

length = <0x300000>;

Is it clear now? Sorry for any confusion.

I'm sorry but not really. You know the end of the physical device and the size of the ART partition, so you must know its start as well?

Quoted 8 lines

Before the system boot we know:
- size of the ART partition
- real size of the physical device (512mb... 1G... 64mb...)

When the physical device is probed (nand) a special driver is loaded (before mtd parsing logic) that change the physical size of the device (mtd->size) as at the end of the nand some space is reserved for bad block management and other metadata info.

Quoted 5 lines

Here you are explaining what you intend Linux to do, right? I would like to understand what you are trying to solve. I dont understand why you need the size change, I don't understand why you don't know the start of the ART partition, I don't understand what the data you are hiding contains and who uses it :-) I'm sorry, this is too unclear yet.

Totally not a problem and thanks a lot for you keep asking them... More than happy to clear things, I'm trying to solve a problem present on Airoha SoC and upstreaming a correct parser for it.

What I'm trying to solve:

Correct access to this partition at the end of the flash in an automated way.

The content of this partition is the usual ART partition found on lots of embedded devices. MAC address, wifi calibration data, serial. Usage is NVMEM cells and userspace with dd command to extract data from.

Airoha use something also used by some mediatek SoC. They call it BMT and it's currently used downstream in OpenWrt and they firmware. This is also used in the bootloader.

The usage of BMT is a custom way to handle bad blocks entirely by software. At the end of the flash some space is reserved where info about all the blocks of the flash are put. I'm not 100% sure about the functionality of this but it can relocate block and do magic things to handle bad blocks. For the scope of this change, the important info is that after the BMT is probed, the operation of "reserving space" is done by reducing the MTD flash size. So from the MTD subsystem, it does see a smaller flash than it actually is.

Quoted 8 lines

Quoted 5 lines

The reserved space change! Across SoC or even devices but the BMT is a must where it's used as bootloader makes use of it and writing to it might confuse the bootloader corrupting data. (one block might be flagged as bad ad data moved, BMT driver validates his table and do operation)

Ok, I think that's way clearer now.

Hi sorry for the delay, very happy this is better now.

Quoted 3 lines

So the BMT driver does not exist in mainline Linux, but you would like to skip this part of the MTD device to avoid smashing it. And it is in use by the vendor Bootloader I guess?

Yes correct, idea is to permit easier access to the partition. I hope (and assume) this driver will come upstream.

Quoted 7 lines

Is it some kind of table that is written by the chip itself in order to maintain a list of auto-replacement blocks for bad blocks? Can the size of this table move with the use of the device? (if yes, it's problematic, we don't want to resize MTD partitions without noticing, it would break eg. UBI).

No chip hw bad block is disabled with this implementation and the table size doesn't move/change so MTD partitions will stay at the same offset after the first parse on boot.

Quoted 8 lines

I believe this BMT block is going against the bad block handling in Linux, so I really wonder how one can use both mechanisms in a system. If the BMT layer takes "one random block" to map a corrupted one on it, it totally defeats the current bad block model we have in MTD/UBI and simply cannot be supported at all. Just skipping the currently-used-for-BMT blocks sounds like a very bad idea that will break your system, later.

Well we disable it and since it's reserved, from the system side you can do all kind of magic since the space used for the driver is not available to the system but I will try to gather more info about this in the next few days.

Quoted 67 lines · Miquel Raynal

Hi Christian,

Quoted 65 lines

Quoted 33 lines

Quoted 24 lines

Quoted 16 lines

Quoted 16 lines

Ok probably the description isn't clear enough. The missing info that require this parser is the flash end.

Following the example we know the size of rootfs_data and start offset AND we know the size of the ART partition.

There might be a space in the middle unused between the rootfs_data partition and the art partition. What is derived is the starting offset of the art partition that is flash end - art partition size. (where flash end change and is not always the same due to how the special bad block managament table reserved space is handled)

This is why 0xffffffff, used as a dummy offset to signal it will be parsed at runtime. On second tought tho maybe using this dummy offset is wrong and I should just have something like

Quoted 7 lines

Quoted 3 lines

length = <0x300000>;

Is it clear now? Sorry for any confusion.

I'm sorry but not really. You know the end of the physical device and the size of the ART partition, so you must know its start as well?

Quoted 8 lines

Before the system boot we know:
- size of the ART partition
- real size of the physical device (512mb... 1G... 64mb...)

When the physical device is probed (nand) a special driver is loaded (before mtd parsing logic) that change the physical size of the device (mtd->size) as at the end of the nand some space is reserved for bad block management and other metadata info.

Quoted 5 lines

Here you are explaining what you intend Linux to do, right? I would like to understand what you are trying to solve. I dont understand why you need the size change, I don't understand why you don't know the start of the ART partition, I don't understand what the data you are hiding contains and who uses it :-) I'm sorry, this is too unclear yet.

Totally not a problem and thanks a lot for you keep asking them... More than happy to clear things, I'm trying to solve a problem present on Airoha SoC and upstreaming a correct parser for it.

What I'm trying to solve:

Correct access to this partition at the end of the flash in an automated way.

The content of this partition is the usual ART partition found on lots of embedded devices. MAC address, wifi calibration data, serial. Usage is NVMEM cells and userspace with dd command to extract data from.

Airoha use something also used by some mediatek SoC. They call it BMT and it's currently used downstream in OpenWrt and they firmware. This is also used in the bootloader.

The usage of BMT is a custom way to handle bad blocks entirely by software. At the end of the flash some space is reserved where info about all the blocks of the flash are put. I'm not 100% sure about the functionality of this but it can relocate block and do magic things to handle bad blocks. For the scope of this change, the important info is that after the BMT is probed, the operation of "reserving space" is done by reducing the MTD flash size. So from the MTD subsystem, it does see a smaller flash than it actually is.

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The reserved space change! Across SoC or even devices but the BMT is a must where it's used as bootloader makes use of it and writing to it might confuse the bootloader corrupting data. (one block might be flagged as bad ad data moved, BMT driver validates his table and do operation)

Ok, I think that's way clearer now.

Hi sorry for the delay, very happy this is better now.

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So the BMT driver does not exist in mainline Linux, but you would like to skip this part of the MTD device to avoid smashing it. And it is in use by the vendor Bootloader I guess?

Yes correct, idea is to permit easier access to the partition. I hope (and assume) this driver will come upstream.

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Is it some kind of table that is written by the chip itself in order to maintain a list of auto-replacement blocks for bad blocks? Can the size of this table move with the use of the device? (if yes, it's problematic, we don't want to resize MTD partitions without noticing, it would break eg. UBI).

No chip hw bad block is disabled with this implementation and the table size doesn't move/change so MTD partitions will stay at the same offset after the first parse on boot.

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I believe this BMT block is going against the bad block handling in Linux, so I really wonder how one can use both mechanisms in a system. If the BMT layer takes "one random block" to map a corrupted one on it, it totally defeats the current bad block model we have in MTD/UBI and simply cannot be supported at all. Just skipping the currently-used-for-BMT blocks sounds like a very bad idea that will break your system, later.

Well we disable it and since it's reserved, from the system side you can do all kind of magic since the space used for the driver is not available to the system but I will try to gather more info about this in the next few days.