[PATCH v2 0/3] MTD physmap: Adding reserved RAM support and fixing reserved_mem limitations

[PATCH v2 0/3] MTD physmap: Adding reserved RAM support and fixing reserved_mem limitations

[Gregory CLEMENT]

Hello,

While working on adding reserved RAM support to the MTD physmap
driver, I encountered a limitation in the kernel's reserved memory
support: although the Device Tree specification allows multiple reg
entries for a memory-region node, the kernel only processed the first
one. This limitation prevented proper support for reserved RAM regions
in MTD.

This series addresses both issues:

First, the reserved memory support is extended to fully support
multiple reg entries per memory-region node, ensuring compliance with
the Device Tree specification.

Then, with this foundation in place, the series updates the MTD
physmap driver to support reserved RAM regions. The DT bindings are
extended to allow memory-region phandles for RAM access, and the
physmap driver is modified to use these regions.

Gregory

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
---
Changes in v2:

- Properly managed cases where register entries used by the memory
  region are out of order, particularly when one or more register
  entries are mixed with memory region entries in an other node.
- Used "memlog" as the node name instead of "sram," which was misleading.
- Link to v1: https://lore.kernel.org/r/20251117-mtd-memregion-v1-0-7b35611c79a6@bootlin.com

---
Gregory CLEMENT (3):
      of: reserved_mem: Support multiple 'reg' entries for memory-region
      dt-bindings: mtd: physmap: Allow using memory-region to access memory resources
      mtd: physmap: Add support for RAM reserved memory regions

 .../devicetree/bindings/mtd/mtd-physmap.yaml       |  59 ++++++---
 drivers/mtd/maps/physmap-core.c                    |  56 +++++++--
 drivers/of/of_reserved_mem.c                       | 139 +++++++++++++++++++--
 include/linux/of_reserved_mem.h                    |   4 +
 4 files changed, 218 insertions(+), 40 deletions(-)
---
base-commit: b55d426c390f2a4762b2a88b113cc44c37e08e46
change-id: 20251117-mtd-memregion-8830c1dd70ce

Best regards,
-- 
Grégory CLEMENT, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com


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http://lists.infradead.org/mailman/listinfo/linux-mtd/

[PATCH v2 1/3] of: reserved_mem: Support multiple 'reg' entries for memory-region

[Gregory CLEMENT]

The Device Tree specification allows a "memory-region" node to have
multiple 'reg' entries, but the current kernel implementation only
processes the first entry. This can lead to drivers not being able to
access all the reserved memory regions specified in the Device Tree.

This patch extends the reserved memory handling to support multiple
'reg' entries for a single "memory-region" node. The existing exported
functions remain unchanged for backward compatibility, but new APIs
are introduced to allow drivers to access all reserved memory regions.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
---
 drivers/of/of_reserved_mem.c    | 139 ++++++++++++++++++++++++++++++++++++----
 include/linux/of_reserved_mem.h |   4 ++
 2 files changed, 131 insertions(+), 12 deletions(-)

diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index 2e9ea751ed2df..ecb3ffe74113f 100644
--- a/drivers/of/of_reserved_mem.c
+++ b/drivers/of/of_reserved_mem.c
@@ -159,6 +159,7 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
 	int len;
 	const __be32 *prop;
 	bool nomap;
+	int count = 0;
 
 	prop = of_get_flat_dt_prop(node, "reg", &len);
 	if (!prop)
@@ -183,6 +184,7 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
 				dma_contiguous_early_fixup(base, size);
 			pr_debug("Reserved memory: reserved region for node '%s': base %pa, size %lu MiB\n",
 				uname, &base, (unsigned long)(size / SZ_1M));
+			count++;
 		} else {
 			pr_err("Reserved memory: failed to reserve memory for node '%s': base %pa, size %lu MiB\n",
 			       uname, &base, (unsigned long)(size / SZ_1M));
@@ -190,7 +192,7 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
 
 		len -= t_len;
 	}
-	return 0;
+	return count;
 }
 
 /*
@@ -235,7 +237,7 @@ void __init fdt_scan_reserved_mem_reg_nodes(void)
 	phys_addr_t base, size;
 	const __be32 *prop;
 	int node, child;
-	int len;
+	int len, i;
 
 	if (!fdt)
 		return;
@@ -273,12 +275,12 @@ void __init fdt_scan_reserved_mem_reg_nodes(void)
 		if (len > t_len)
 			pr_warn("%s() ignores %d regions in node '%s'\n",
 				__func__, len / t_len - 1, uname);
-
-		base = dt_mem_next_cell(dt_root_addr_cells, &prop);
-		size = dt_mem_next_cell(dt_root_size_cells, &prop);
-
-		if (size)
-			fdt_reserved_mem_save_node(child, uname, base, size);
+		for (i = 0; i < len; i += t_len) {
+			base = dt_mem_next_cell(dt_root_addr_cells, &prop);
+			size = dt_mem_next_cell(dt_root_size_cells, &prop);
+			if (size)
+				fdt_reserved_mem_save_node(child, uname, base, size);
+		}
 	}
 
 	/* check for overlapping reserved regions */
@@ -308,16 +310,16 @@ int __init fdt_scan_reserved_mem(void)
 
 	fdt_for_each_subnode(child, fdt, node) {
 		const char *uname;
-		int err;
+		int err, ret;
 
 		if (!of_fdt_device_is_available(fdt, child))
 			continue;
 
 		uname = fdt_get_name(fdt, child, NULL);
 
-		err = __reserved_mem_reserve_reg(child, uname);
-		if (!err)
-			count++;
+		ret = __reserved_mem_reserve_reg(child, uname);
+		if (ret > 0)
+			count += ret;
 		/*
 		 * Save the nodes for the dynamically-placed regions
 		 * into an array which will be used for allocation right
@@ -750,6 +752,35 @@ struct reserved_mem *of_reserved_mem_lookup(struct device_node *np)
 }
 EXPORT_SYMBOL_GPL(of_reserved_mem_lookup);
 
+/**
+ * of_reserved_mem_array_lookup() - acquire reserved_mem array from a device node
+ * @np:		node pointer of the desired reserved-memory region
+ * @rmrm:	pointer to the first elemennt of the reserved_mem struct of the memory region
+ *
+ * This function allows drivers to acquire a reference to the array of the
+ *  reserved_mem struct based on a device node handle.
+ *
+ * Returns the number reserved_mem elements
+ */
+int of_reserved_mem_array_lookup(struct device_node *np,
+				 struct reserved_mem **rmem)
+{
+	const char *name;
+	int i, count = 0;
+
+	if (!np->full_name)
+		return 0;
+
+	name = kbasename(np->full_name);
+
+	for (i = 0; i < reserved_mem_count; i++)
+		if (!strcmp(reserved_mem[i].name, name))
+			rmem[count++] = &reserved_mem[i];
+
+	return count;
+}
+EXPORT_SYMBOL_GPL(of_reserved_mem_array_lookup);
+
 /**
  * of_reserved_mem_region_to_resource() - Get a reserved memory region as a resource
  * @np:		node containing 'memory-region' property
@@ -785,6 +816,49 @@ int of_reserved_mem_region_to_resource(const struct device_node *np,
 }
 EXPORT_SYMBOL_GPL(of_reserved_mem_region_to_resource);
 
+/**
+ * of_reserved_mem_region_to_resource_array() - Get a reserved memory region as a resources
+ * @dev:	device associated to the node
+ * @np:		node containing 'memory-region' property
+ * @idx:	index of 'memory-region' property to lookup
+ * @res:	Pointer to an array of struct resource pointers to fill in with reserved regions
+ *
+ * This function allows drivers to lookup a node's 'memory-region' property
+ * entries by index and fill an array of struct resource pointers for the entries.
+ *
+ * Returns the number of resources filled in @res on success.
+ * Returns -ENODEV if 'memory-region' is missing or unavailable,
+ * -EINVAL for any other error.
+ */
+int of_reserved_mem_region_to_resource_array(struct device *dev, const struct device_node *np,
+					     unsigned int idx, struct resource **res)
+{
+	struct reserved_mem *rmem[MAX_RESERVED_REGIONS];
+	int count, i;
+	struct resource *r;
+
+	if (!np)
+		return -EINVAL;
+
+	struct device_node __free(device_node) *target = of_parse_phandle(np, "memory-region", idx);
+	if (!target || !of_device_is_available(target))
+		return -ENODEV;
+
+	count = of_reserved_mem_array_lookup(target, rmem);
+	if (count <= 0)
+		return -EINVAL;
+
+	*res = devm_kzalloc(dev, count * sizeof(struct resource), GFP_KERNEL);
+	r = res[0];
+	for (i = 0; i < count; i++) {
+		resource_set_range(&r[i], rmem[i]->base, rmem[i]->size);
+		r[i].flags = IORESOURCE_MEM;
+		r[i].name = rmem[i]->name;
+	}
+	return count;
+}
+EXPORT_SYMBOL_GPL(of_reserved_mem_region_to_resource_array);
+
 /**
  * of_reserved_mem_region_to_resource_byname() - Get a reserved memory region as a resource
  * @np:		node containing 'memory-region' property
@@ -829,3 +903,44 @@ int of_reserved_mem_region_count(const struct device_node *np)
 	return of_count_phandle_with_args(np, "memory-region", NULL);
 }
 EXPORT_SYMBOL_GPL(of_reserved_mem_region_count);
+
+/**
+ * of_reserved_mem_region_count() - Return the total number of reserved memory regions
+ * @np:		node containing 'memory-region' property
+ *
+ * This function counts the total number of reserved memory regions referenced
+ * by a node's 'memory-region' property. It iterates over each phandle and sums
+ * the number of regions found in each referenced reserved memory node.
+ *
+ * Returns the total number of reserved memory regions on success.
+ * This function allows drivers to retrieve the number of entries for a node's
+ * 'memory-region' property.
+ *
+ * Returns total number of reserved memory regions on success, or negative error
+ * code on a malformed property.
+ */
+int of_reserved_mem_region_total_count(const struct device_node *np)
+{
+	int nregion = of_count_phandle_with_args(np, "memory-region", NULL);
+	struct device_node *target;
+	int i, nregs = 0;
+
+	for (i = 0; i < nregion; i++) {
+		struct reserved_mem *rmem;
+
+		target = of_parse_phandle(np, "memory-region", i);
+		if (!target)
+			return -ENODEV;
+
+		if (!of_device_is_available(target)) {
+			of_node_put(target);
+			return 0;
+		}
+
+		nregs += of_reserved_mem_array_lookup(target, &rmem);
+
+		of_node_put(target);
+	};
+	return nregs;
+}
+EXPORT_SYMBOL_GPL(of_reserved_mem_region_total_count);
diff --git a/include/linux/of_reserved_mem.h b/include/linux/of_reserved_mem.h
index f573423359f48..1e0c6afddd812 100644
--- a/include/linux/of_reserved_mem.h
+++ b/include/linux/of_reserved_mem.h
@@ -40,11 +40,15 @@ int of_reserved_mem_device_init_by_name(struct device *dev,
 void of_reserved_mem_device_release(struct device *dev);
 
 struct reserved_mem *of_reserved_mem_lookup(struct device_node *np);
+int of_reserved_mem_array_lookup(struct device_node *np, struct reserved_mem **rmem);
 int of_reserved_mem_region_to_resource(const struct device_node *np,
 				       unsigned int idx, struct resource *res);
+int of_reserved_mem_region_to_resource_array(struct device *dev, const struct device_node *np,
+					     unsigned int idx, struct resource **res);
 int of_reserved_mem_region_to_resource_byname(const struct device_node *np,
 					      const char *name, struct resource *res);
 int of_reserved_mem_region_count(const struct device_node *np);
+int of_reserved_mem_region_total_count(const struct device_node *np);
 
 #else
 

-- 
2.51.0


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[PATCH v2 2/3] dt-bindings: mtd: physmap: Allow using memory-region to access memory resources

[Gregory CLEMENT]

Enable access to memory resources not only via I/O address using reg,
but also through a portion of main memory using memory-region. To
achieve this, new compatible strings have been introduced: mtd-mem and
mtd-memro.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
---
 .../devicetree/bindings/mtd/mtd-physmap.yaml       | 59 +++++++++++++++-------
 1 file changed, 40 insertions(+), 19 deletions(-)

diff --git a/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml b/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
index 1b375dee83b0c..323e89aacaacd 100644
--- a/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
+++ b/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
@@ -13,10 +13,6 @@ description: |
   Flash chips (Memory Technology Devices) are often used for solid state
   file systems on embedded devices.
 
-allOf:
-  - $ref: mtd.yaml#
-  - $ref: /schemas/memory-controllers/mc-peripheral-props.yaml#
-
 properties:
   compatible:
     oneOf:
@@ -61,6 +57,8 @@ properties:
           - jedec-flash
           - mtd-ram
           - mtd-rom
+          - mtd-mem
+          - mtd-memro
 
   reg:
     description: |
@@ -116,6 +114,10 @@ properties:
     minItems: 1
     maxItems: 8
 
+  memory-region:
+    items:
+      - description: Memory regions to map into mtd
+
   '#address-cells':
     const: 1
 
@@ -129,21 +131,25 @@ properties:
 
 required:
   - compatible
-  - reg
-
-if:
-  properties:
-    compatible:
-      contains:
-        const: cortina,gemini-flash
-then:
-  properties:
-    syscon:
-      $ref: /schemas/types.yaml#/definitions/phandle
-      description:
-        Phandle to the syscon controller
-  required:
-    - syscon
+
+allOf:
+  - $ref: mtd.yaml#
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - mtd-mem
+              - mtd-memro
+    then:
+      required:
+        - memory-region
+      properties:
+        addr-gpios: false
+    else:
+      $ref: /schemas/memory-controllers/mc-peripheral-props.yaml#
+      required:
+        - reg
 
 unevaluatedProperties: false
 
@@ -223,4 +229,19 @@ examples:
             reg = <0 0x04000000>;
         };
     };
+
+  - |
+    /* An example using mtd-mem */
+    mem_logs: mem_logs@10000800 {
+        reg = <0x1 0x0000800 0x0 0x000f800>;
+        no-map;
+    };
+
+    memlog {
+        compatible = "mtd-mem";
+        memory-region = <&mem_log>;
+        bank-width = <4>;
+        device-width = <1>;
+    };
+
 ...

-- 
2.51.0


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[PATCH v2 3/3] mtd: physmap: Add support for RAM reserved memory regions

[Gregory CLEMENT]

MTD fixed-partitions can now be exposed for reserved RAM regions, not
just ROM reg regions. This is achieved by using a memory-region
phandle to reference the reserved RAM region instead of the reg
property.

Based on the work of Muhammad Musa <muhammad.musa@intel.com>

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
---
 drivers/mtd/maps/physmap-core.c | 56 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 47 insertions(+), 9 deletions(-)

diff --git a/drivers/mtd/maps/physmap-core.c b/drivers/mtd/maps/physmap-core.c
index 2bd7a1af898c9..f084f6f34d611 100644
--- a/drivers/mtd/maps/physmap-core.c
+++ b/drivers/mtd/maps/physmap-core.c
@@ -39,6 +39,7 @@
 #include <linux/mtd/cfi_endian.h>
 #include <linux/io.h>
 #include <linux/of.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/pm_runtime.h>
 #include <linux/gpio/consumer.h>
 
@@ -263,6 +264,14 @@ static const struct of_device_id of_flash_match[] = {
 		.type = "rom",
 		.compatible = "direct-mapped"
 	},
+	{
+		.compatible = "mtd-mem",
+		.data = "map_ram",
+	},
+	{
+		.compatible = "mtd-memro",
+		.data = "map_rom",
+	},
 	{ /* sentinel */ },
 };
 MODULE_DEVICE_TABLE(of, of_flash_match);
@@ -446,8 +455,9 @@ static int physmap_flash_pdata_init(struct platform_device *dev)
 static int physmap_flash_probe(struct platform_device *dev)
 {
 	struct physmap_flash_info *info;
-	int err = 0;
-	int i;
+	struct resource *res_array;
+	int err = 0, is_rsvd_mem = 0, nreg = 0;
+	int i, curr_reg;
 
 	if (!dev->dev.of_node && !dev_get_platdata(&dev->dev))
 		return -EINVAL;
@@ -459,9 +469,13 @@ static int physmap_flash_probe(struct platform_device *dev)
 	while (platform_get_resource(dev, IORESOURCE_MEM, info->nmaps))
 		info->nmaps++;
 
-	if (!info->nmaps)
-		return -ENODEV;
-
+	if (!info->nmaps) {
+		info->nmaps = of_reserved_mem_region_total_count(dev->dev.of_node);
+		if (info->nmaps > 0)
+			is_rsvd_mem = 1;
+		else
+			return -ENODEV;
+	}
 	info->maps = devm_kzalloc(&dev->dev,
 				  sizeof(*info->maps) * info->nmaps,
 				  GFP_KERNEL);
@@ -503,7 +517,23 @@ static int physmap_flash_probe(struct platform_device *dev)
 	for (i = 0; i < info->nmaps; i++) {
 		struct resource *res;
 
-		info->maps[i].virt = devm_platform_get_and_ioremap_resource(dev, i, &res);
+		if (is_rsvd_mem) {
+			if (nreg <= i) {
+				int cnt = of_reserved_mem_region_to_resource_array(&dev->dev,
+							   dev->dev.of_node, i, &res_array);
+				if (cnt < 0) {
+					err = cnt;
+					goto err_out;
+				}
+				nreg += cnt;
+				curr_reg = 0;
+			}
+			res = &res_array[curr_reg++];
+			info->maps[i].virt = devm_ioremap_resource(&dev->dev, res);
+		} else {
+			info->maps[i].virt = devm_platform_get_and_ioremap_resource(dev, i, &res);
+		}
+
 		if (IS_ERR(info->maps[i].virt)) {
 			err = PTR_ERR(info->maps[i].virt);
 			goto err_out;
@@ -519,9 +549,17 @@ static int physmap_flash_probe(struct platform_device *dev)
 			info->maps[i].phys = res->start;
 
 		info->win_order = fls64(resource_size(res)) - 1;
-		info->maps[i].size = BIT(info->win_order +
-					 (info->gpios ?
-					  info->gpios->ndescs : 0));
+		/* When using a memory region, the size is not necessarily a
+		 * power of 2, so win_order is not applicable. Since GPIOs are
+		 * unavailable in this context, directly using the region's size
+		 * is safe.
+		 */
+		if (is_rsvd_mem)
+			info->maps[i].size = resource_size(res);
+		else
+			info->maps[i].size = BIT(info->win_order +
+						 (info->gpios ?
+						  info->gpios->ndescs : 0));
 
 		info->maps[i].map_priv_1 = (unsigned long)dev;
 

-- 
2.51.0


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Re: [PATCH v2 2/3] dt-bindings: mtd: physmap: Allow using memory-region to access memory resources

[Rob Herring (Arm)]

On Fri, 21 Nov 2025 16:42:36 +0100, Gregory CLEMENT wrote:
> Enable access to memory resources not only via I/O address using reg,
> but also through a portion of main memory using memory-region. To
> achieve this, new compatible strings have been introduced: mtd-mem and
> mtd-memro.
> 
> Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
> ---
>  .../devicetree/bindings/mtd/mtd-physmap.yaml       | 59 +++++++++++++++-------
>  1 file changed, 40 insertions(+), 19 deletions(-)
> 

My bot found errors running 'make dt_binding_check' on your patch:

yamllint warnings/errors:

dtschema/dtc warnings/errors:
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/mtd/mtd-physmap.example.dtb: memlog (mtd-mem): $nodename:0: 'memlog' does not match '^(flash|.*sram|nand)(@.*)?$'
	from schema $id: http://devicetree.org/schemas/mtd/mtd-physmap.yaml

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/20251121-mtd-memregion-v2-2-c5535fdcebe4@bootlin.com

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.


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Re: [PATCH v2 1/3] of: reserved_mem: Support multiple 'reg' entries for memory-region

[Krzysztof Kozlowski]

On Fri, Nov 21, 2025 at 04:42:35PM +0100, Gregory CLEMENT wrote:
> + * This function allows drivers to lookup a node's 'memory-region' property
> + * entries by index and fill an array of struct resource pointers for the entries.
> + *
> + * Returns the number of resources filled in @res on success.
> + * Returns -ENODEV if 'memory-region' is missing or unavailable,
> + * -EINVAL for any other error.
> + */
> +int of_reserved_mem_region_to_resource_array(struct device *dev, const struct device_node *np,
> +					     unsigned int idx, struct resource **res)
> +{
> +	struct reserved_mem *rmem[MAX_RESERVED_REGIONS];
> +	int count, i;
> +	struct resource *r;
> +
> +	if (!np)
> +		return -EINVAL;
> +
> +	struct device_node __free(device_node) *target = of_parse_phandle(np, "memory-region", idx);

Odd cleanup placement. Please read cleanup.h. Also please run checkpatch
because it told you this - marked it as ERROR.

Best regards,
Krzysztof


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Re: [PATCH v2 2/3] dt-bindings: mtd: physmap: Allow using memory-region to access memory resources

[Rob Herring]

On Fri, Nov 21, 2025 at 04:42:36PM +0100, Gregory CLEMENT wrote:
> Enable access to memory resources not only via I/O address using reg,
> but also through a portion of main memory using memory-region. To
> achieve this, new compatible strings have been introduced: mtd-mem and
> mtd-memro.
> 
> Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
> ---
>  .../devicetree/bindings/mtd/mtd-physmap.yaml       | 59 +++++++++++++++-------
>  1 file changed, 40 insertions(+), 19 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml b/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
> index 1b375dee83b0c..323e89aacaacd 100644
> --- a/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
> +++ b/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
> @@ -13,10 +13,6 @@ description: |
>    Flash chips (Memory Technology Devices) are often used for solid state
>    file systems on embedded devices.
>  
> -allOf:
> -  - $ref: mtd.yaml#
> -  - $ref: /schemas/memory-controllers/mc-peripheral-props.yaml#
> -
>  properties:
>    compatible:
>      oneOf:
> @@ -61,6 +57,8 @@ properties:
>            - jedec-flash
>            - mtd-ram
>            - mtd-rom
> +          - mtd-mem
> +          - mtd-memro
>  
>    reg:
>      description: |
> @@ -116,6 +114,10 @@ properties:
>      minItems: 1
>      maxItems: 8
>  
> +  memory-region:
> +    items:
> +      - description: Memory regions to map into mtd
> +
>    '#address-cells':
>      const: 1
>  
> @@ -129,21 +131,25 @@ properties:
>  
>  required:
>    - compatible
> -  - reg
> -
> -if:
> -  properties:
> -    compatible:
> -      contains:
> -        const: cortina,gemini-flash
> -then:
> -  properties:
> -    syscon:
> -      $ref: /schemas/types.yaml#/definitions/phandle
> -      description:
> -        Phandle to the syscon controller
> -  required:
> -    - syscon
> +
> +allOf:
> +  - $ref: mtd.yaml#
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - mtd-mem
> +              - mtd-memro
> +    then:
> +      required:
> +        - memory-region
> +      properties:
> +        addr-gpios: false
> +    else:
> +      $ref: /schemas/memory-controllers/mc-peripheral-props.yaml#
> +      required:
> +        - reg
>  
>  unevaluatedProperties: false
>  
> @@ -223,4 +229,19 @@ examples:
>              reg = <0 0x04000000>;
>          };
>      };
> +
> +  - |
> +    /* An example using mtd-mem */
> +    mem_logs: mem_logs@10000800 {
> +        reg = <0x1 0x0000800 0x0 0x000f800>;
> +        no-map;
> +    };
> +
> +    memlog {
> +        compatible = "mtd-mem";
> +        memory-region = <&mem_log>;
> +        bank-width = <4>;
> +        device-width = <1>;
> +    };

To repeat v1 comment:

> If we do keep this, I'd rather just add the properties below into the
> /reserved-memory node itself. Devices are created for those nodes if
> they have 'compatible'.

To put it another way, see the ramoops binding and copy that.

Rob

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