nvmem: core: skip child nodes not matching binding

The nvmem cell binding applies to all eeprom child nodes matching
"^.*@[0-9a-f]+$" without taking a compatible into account.

Linux drivers, like at24, are even more extensive and assume
_all_ at24 eeprom child nodes to be nvmem cells since e888d445ac
("nvmem: resolve cells from DT at registration time").

Since df5f3b6f53 ("dt-bindings: nvmem: stm32: new property for
data access"), the additionalProperties: True means it's Ok to have
other properties as long as they don't match "^.*@[0-9a-f]+$".

The barebox bootloader extends the MTD partitions binding to
EEPROM and can fix up following device tree node:

  &eeprom {
    partitions {
      compatible = "fixed-partitions";
    };
  };

This is allowed binding-wise, but drivers using nvmem_register()
like at24 will fail to parse because the function expects all child
nodes to have a reg property present. This results in the whole
EEPROM driver probe failing despite the device tree being correct.

Fix this by skipping nodes lacking a reg property instead of
returning an error. This effectively makes the drivers adhere
to the binding because all nodes with a unit address must have
a reg property and vice versa.

Fixes: e888d445ac ("nvmem: resolve cells from DT at registration time").
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210129171430.11328-6-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -682,7 +682,9 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
 
 	for_each_child_of_node(parent, child) {
 		addr = of_get_property(child, "reg", &len);
-		if (!addr || (len < 2 * sizeof(u32))) {
+		if (!addr)
+			continue;
+		if (len < 2 * sizeof(u32)) {
 			dev_err(dev, "nvmem: invalid reg on %pOF\n", child);
 			return -EINVAL;
 		}