nvmem: core: introduce NVMEM layouts

NVMEM layouts are used to generate NVMEM cells during runtime. Think of
an EEPROM with a well-defined conent. For now, the content can be
described by a device tree or a board file. But this only works if the
offsets and lengths are static and don't change. One could also argue
that putting the layout of the EEPROM in the device tree is the wrong
place. Instead, the device tree should just have a specific compatible
string.

Right now there are two use cases:
 (1) The NVMEM cell needs special processing. E.g. if it only specifies
     a base MAC address offset and you need to add an offset, or it
     needs to parse a MAC from ASCII format or some proprietary format.
     (Post processing of cells is added in a later commit).
 (2) u-boot environment parsing. The cells don't have a particular
     offset but it needs parsing the content to determine the offsets
     and length.

Co-developed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230404172148.82422-14-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

5 files changed, 134 insertions, 0 deletions

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 3b3832f4dfad..a2afba11c890 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -21,6 +21,10 @@ config NVMEM_SYSFS
 	 This interface is mostly used by userspace applications to
 	 read/write directly into nvmem.
 
+# Layouts
+
+source "drivers/nvmem/layouts/Kconfig"
+
 # Devices
 
 config NVMEM_APPLE_EFUSES
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 6a1efffa88f0..f82431ec8aef 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -5,6 +5,7 @@
 
 obj-$(CONFIG_NVMEM)		+= nvmem_core.o
 nvmem_core-y			:= core.o
+obj-y				+= layouts/
 
 # Devices
 obj-$(CONFIG_NVMEM_APPLE_EFUSES)	+= nvmem-apple-efuses.o
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 22024b830788..b9be1faeb7be 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -40,6 +40,7 @@ struct nvmem_device {
 	nvmem_reg_write_t	reg_write;
 	nvmem_cell_post_process_t cell_post_process;
 	struct gpio_desc	*wp_gpio;
+	struct nvmem_layout	*layout;
 	void *priv;
 };
 
@@ -74,6 +75,9 @@ static LIST_HEAD(nvmem_lookup_list);
 
 static BLOCKING_NOTIFIER_HEAD(nvmem_notifier);
 
+static DEFINE_SPINLOCK(nvmem_layout_lock);
+static LIST_HEAD(nvmem_layouts);
+
 static int __nvmem_reg_read(struct nvmem_device *nvmem, unsigned int offset,
 			    void *val, size_t bytes)
 {
@@ -728,6 +732,101 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
 	return 0;
 }
 
+int __nvmem_layout_register(struct nvmem_layout *layout, struct module *owner)
+{
+	layout->owner = owner;
+
+	spin_lock(&nvmem_layout_lock);
+	list_add(&layout->node, &nvmem_layouts);
+	spin_unlock(&nvmem_layout_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__nvmem_layout_register);
+
+void nvmem_layout_unregister(struct nvmem_layout *layout)
+{
+	spin_lock(&nvmem_layout_lock);
+	list_del(&layout->node);
+	spin_unlock(&nvmem_layout_lock);
+}
+EXPORT_SYMBOL_GPL(nvmem_layout_unregister);
+
+static struct nvmem_layout *nvmem_layout_get(struct nvmem_device *nvmem)
+{
+	struct device_node *layout_np, *np = nvmem->dev.of_node;
+	struct nvmem_layout *l, *layout = NULL;
+
+	layout_np = of_get_child_by_name(np, "nvmem-layout");
+	if (!layout_np)
+		return NULL;
+
+	spin_lock(&nvmem_layout_lock);
+
+	list_for_each_entry(l, &nvmem_layouts, node) {
+		if (of_match_node(l->of_match_table, layout_np)) {
+			if (try_module_get(l->owner))
+				layout = l;
+
+			break;
+		}
+	}
+
+	spin_unlock(&nvmem_layout_lock);
+	of_node_put(layout_np);
+
+	return layout;
+}
+
+static void nvmem_layout_put(struct nvmem_layout *layout)
+{
+	if (layout)
+		module_put(layout->owner);
+}
+
+static int nvmem_add_cells_from_layout(struct nvmem_device *nvmem)
+{
+	struct nvmem_layout *layout = nvmem->layout;
+	int ret;
+
+	if (layout && layout->add_cells) {
+		ret = layout->add_cells(&nvmem->dev, nvmem, layout);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+#if IS_ENABLED(CONFIG_OF)
+/**
+ * of_nvmem_layout_get_container() - Get OF node to layout container.
+ *
+ * @nvmem: nvmem device.
+ *
+ * Return: a node pointer with refcount incremented or NULL if no
+ * container exists. Use of_node_put() on it when done.
+ */
+struct device_node *of_nvmem_layout_get_container(struct nvmem_device *nvmem)
+{
+	return of_get_child_by_name(nvmem->dev.of_node, "nvmem-layout");
+}
+EXPORT_SYMBOL_GPL(of_nvmem_layout_get_container);
+#endif
+
+const void *nvmem_layout_get_match_data(struct nvmem_device *nvmem,
+					struct nvmem_layout *layout)
+{
+	struct device_node __maybe_unused *layout_np;
+	const struct of_device_id *match;
+
+	layout_np = of_nvmem_layout_get_container(nvmem);
+	match = of_match_node(layout->of_match_table, layout_np);
+
+	return match ? match->data : NULL;
+}
+EXPORT_SYMBOL_GPL(nvmem_layout_get_match_data);
+
 /**
  * nvmem_register() - Register a nvmem device for given nvmem_config.
  * Also creates a binary entry in /sys/bus/nvmem/devices/dev-name/nvmem
@@ -834,6 +933,12 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 			goto err_put_device;
 	}
 
+	/*
+	 * If the driver supplied a layout by config->layout, the module
+	 * pointer will be NULL and nvmem_layout_put() will be a noop.
+	 */
+	nvmem->layout = config->layout ?: nvmem_layout_get(nvmem);
+
 	if (config->cells) {
 		rval = nvmem_add_cells(nvmem, config->cells, config->ncells);
 		if (rval)
@@ -854,12 +959,17 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	if (rval)
 		goto err_remove_cells;
 
+	rval = nvmem_add_cells_from_layout(nvmem);
+	if (rval)
+		goto err_remove_cells;
+
 	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
 
 	return nvmem;
 
 err_remove_cells:
 	nvmem_device_remove_all_cells(nvmem);
+	nvmem_layout_put(nvmem->layout);
 	if (config->compat)
 		nvmem_sysfs_remove_compat(nvmem, config);
 err_put_device:
@@ -881,6 +991,7 @@ static void nvmem_device_release(struct kref *kref)
 		device_remove_bin_file(nvmem->base_dev, &nvmem->eeprom);
 
 	nvmem_device_remove_all_cells(nvmem);
+	nvmem_layout_put(nvmem->layout);
 	device_unregister(&nvmem->dev);
 }
 
@@ -1246,6 +1357,15 @@ struct nvmem_cell *of_nvmem_cell_get(struct device_node *np, const char *id)
 		return ERR_PTR(-EINVAL);
 	}
 
+	/* nvmem layouts produce cells within the nvmem-layout container */
+	if (of_node_name_eq(nvmem_np, "nvmem-layout")) {
+		nvmem_np = of_get_next_parent(nvmem_np);
+		if (!nvmem_np) {
+			of_node_put(cell_np);
+			return ERR_PTR(-EINVAL);
+		}
+	}
+
 	nvmem = __nvmem_device_get(nvmem_np, device_match_of_node);
 	of_node_put(nvmem_np);
 	if (IS_ERR(nvmem)) {
diff --git a/drivers/nvmem/layouts/Kconfig b/drivers/nvmem/layouts/Kconfig
new file mode 100644
index 000000000000..9ad3911d1605
--- /dev/null
+++ b/drivers/nvmem/layouts/Kconfig
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menu "Layout Types"
+
+endmenu
diff --git a/drivers/nvmem/layouts/Makefile b/drivers/nvmem/layouts/Makefile
new file mode 100644
index 000000000000..6fdb3c60a4fa
--- /dev/null
+++ b/drivers/nvmem/layouts/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for nvmem layouts.
+#