nvmem: core: handle the absence of expected layouts

Make nvmem_layout_get() return -EPROBE_DEFER while the expected layout
is not available. This condition cannot be triggered today as nvmem
layout drivers are initialed as part of an early init call, but soon
these drivers will be converted into modules and be initialized with a
standard priority, so the unavailability of the drivers might become a
reality that must be taken care of.

Let's anticipate this by telling the caller the layout might not yet be
available. A probe deferral is requested in this case.

Please note this does not affect any nvmem device not using layouts,
because an early check against the "nvmem-layout" container presence
will return NULL in this case.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Tested-by: Michael Walle <michael@walle.cc>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230404172148.82422-15-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -755,7 +755,7 @@ 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;
+	struct nvmem_layout *l, *layout = ERR_PTR(-EPROBE_DEFER);
 
 	layout_np = of_get_child_by_name(np, "nvmem-layout");
 	if (!layout_np)
@@ -938,6 +938,13 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	 * pointer will be NULL and nvmem_layout_put() will be a noop.
 	 */
 	nvmem->layout = config->layout ?: nvmem_layout_get(nvmem);
+	if (IS_ERR(nvmem->layout)) {
+		rval = PTR_ERR(nvmem->layout);
+		nvmem->layout = NULL;
+
+		if (rval == -EPROBE_DEFER)
+			goto err_teardown_compat;
+	}
 
 	if (config->cells) {
 		rval = nvmem_add_cells(nvmem, config->cells, config->ncells);
@@ -970,6 +977,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 err_remove_cells:
 	nvmem_device_remove_all_cells(nvmem);
 	nvmem_layout_put(nvmem->layout);
+err_teardown_compat:
 	if (config->compat)
 		nvmem_sysfs_remove_compat(nvmem, config);
 err_put_device: