nvmem: layouts: add fixed cells layout

This adds a driver for the "fixed-layout" NVMEM layout binding. It
allows defining NVMEM cells in a layout DT node named "nvmem-layout".

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

drivers/nvmem/layouts/Kconfig

@@ -2,6 +2,14 @@
 
 menu "Layout Types"
 
+config NVMEM_LAYOUT_FIXED
+	tristate "Fixed cells layout support"
+	help
+	  Say Y here if you want to support layout with fixed cells (hardcoded
+	  offsets and sizes).
+
+	  If unsure, say N.
+
 config NVMEM_LAYOUT_SL28_VPD
 	tristate "Kontron sl28 VPD layout support"
 	select CRC8

drivers/nvmem/layouts/Makefile

@@ -3,5 +3,6 @@
 # Makefile for nvmem layouts.
 #
 
+obj-$(CONFIG_NVMEM_LAYOUT_FIXED) += fixed.o
 obj-$(CONFIG_NVMEM_LAYOUT_SL28_VPD) += sl28vpd.o
 obj-$(CONFIG_NVMEM_LAYOUT_ONIE_TLV) += onie-tlv.o

drivers/nvmem/layouts/fixed.c

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/module.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
+
+static int fixed_add_cells(struct device *dev, struct nvmem_device *nvmem,
+			   struct nvmem_layout *layout)
+{
+	struct device_node *layout_np;
+	int err;
+
+	layout_np = of_nvmem_layout_get_container(nvmem);
+	if (!layout_np)
+		return -ENOENT;
+
+	err = nvmem_add_cells_from_of(nvmem, layout_np);
+
+	of_node_put(layout_np);
+
+	return err;
+}
+
+static const struct of_device_id fixed_of_match_table[] = {
+	{ .compatible = "fixed-layout" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, fixed_of_match_table);
+
+struct nvmem_layout fixed_nvmem_layout = {
+	.name = "fixed-layout",
+	.of_match_table = fixed_of_match_table,
+	.add_cells = fixed_add_cells,
+};
+
+module_nvmem_layout_driver(fixed_nvmem_layout);
+
+MODULE_AUTHOR("Rafał Miłecki");
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(of, fixed_of_match_table);