nvmem: core: add support for fixed cells *layout*

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

While NVMEM subsystem supports layout drivers it has been discussed that
"fixed-layout" may actually be supperted internally. It's because:
1. It's a very basic layout
2. It allows sharing code with legacy syntax parsing
3. It's safer for soc_device_match() due to -EPROBE_DEFER
4. This will make the syntax transition easier
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Michael Walle <michael@walle.cc>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Message-ID: <20230611140330.154222-26-srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -696,7 +696,7 @@ static int nvmem_validate_keepouts(struct nvmem_device *nvmem)
 	return 0;
 }
 
-static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
+static int nvmem_add_cells_from_dt(struct nvmem_device *nvmem, struct device_node *np)
 {
 	struct nvmem_layout *layout = nvmem->layout;
 	struct device *dev = &nvmem->dev;
@@ -704,7 +704,7 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
 	const __be32 *addr;
 	int len, ret;
 
-	for_each_child_of_node(dev->of_node, child) {
+	for_each_child_of_node(np, child) {
 		struct nvmem_cell_info info = {0};
 
 		addr = of_get_property(child, "reg", &len);
@@ -742,6 +742,28 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
 	return 0;
 }
 
+static int nvmem_add_cells_from_legacy_of(struct nvmem_device *nvmem)
+{
+	return nvmem_add_cells_from_dt(nvmem, nvmem->dev.of_node);
+}
+
+static int nvmem_add_cells_from_fixed_layout(struct nvmem_device *nvmem)
+{
+	struct device_node *layout_np;
+	int err = 0;
+
+	layout_np = of_nvmem_layout_get_container(nvmem);
+	if (!layout_np)
+		return 0;
+
+	if (of_device_is_compatible(layout_np, "fixed-layout"))
+		err = nvmem_add_cells_from_dt(nvmem, layout_np);
+
+	of_node_put(layout_np);
+
+	return err;
+}
+
 int __nvmem_layout_register(struct nvmem_layout *layout, struct module *owner)
 {
 	layout->owner = owner;
@@ -972,7 +994,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	if (rval)
 		goto err_remove_cells;
 
-	rval = nvmem_add_cells_from_of(nvmem);
+	rval = nvmem_add_cells_from_legacy_of(nvmem);
 	if (rval)
 		goto err_remove_cells;
 
@@ -982,6 +1004,10 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	if (rval)
 		goto err_remove_cells;
 
+	rval = nvmem_add_cells_from_fixed_layout(nvmem);
+	if (rval)
+		goto err_remove_cells;
+
 	rval = nvmem_add_cells_from_layout(nvmem);
 	if (rval)
 		goto err_remove_cells;