[PATCH 4/4] nvmem: make id optional for of_nvmem_device_get()

[Marco Felsch]

Port upstream linux commit
8<----------------------------------------------------------------------
commit d4e7fef1a9a5d2bf3f859ba9f50f4d5409a09ab0
Author: Alban Bedel <albeu at free.fr>
Date:   Mon Jan 28 15:55:03 2019 +0000

    nvmem: core: Properly handle connection ID in of_nvmem_device_get()

    of_nvmem_device_get() would crash if NULL was passed as a connection
    ID. Rework this to use the usual sementic of assuming the first
    connection when no connection ID is given.

    Furthermore of_nvmem_device_get() would return -EINVAL when it failed
    to resolve the connection, making it impossible to properly implement
    an optional connection. Return -ENOENT instead to let the caller know
    that the connection doesn't exists.

    Signed-off-by: Alban Bedel <albeu at free.fr>
    Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla at linaro.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
8<----------------------------------------------------------------------

Signed-off-by: Marco Felsch <m.felsch at pengutronix.de>
---
 drivers/nvmem/core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index b9af31f4b5..9b55f47b4c 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -284,13 +284,14 @@ struct nvmem_device *of_nvmem_device_get(struct device_node *np, const char *id)
 {
 
 	struct device_node *nvmem_np;
-	int index;
+	int index = 0;
 
-	index = of_property_match_string(np, "nvmem-names", id);
+	if (id)
+		index = of_property_match_string(np, "nvmem-names", id);
 
 	nvmem_np = of_parse_phandle(np, "nvmem", index);
 	if (!nvmem_np)
-		return ERR_PTR(-EINVAL);
+		return ERR_PTR(-ENOENT);
 
 	return __nvmem_device_get(nvmem_np, NULL, NULL);
 }
-- 
2.20.1