From: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Date: Fri, 03 Apr 2020 19:50:03 +0200
Subject: add removed helper syscon_regmap_lookup_by_pdevname

The helper syscon_regmap_lookup_by_pdevname has been removed in 29d14b668d2f
("mfd: Remove unused helper syscon_regmap_lookup_by_pdevname") due to lack
of users.

Thus, we have to maintain it locally.

This patch includes a fix due to changes in driver_find_device;
kernel commit: 92ce7e83b4e5 ("driver_find_device: Unify the match function
with class_find_device()")

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

--- a/drivers/mfd/syscon.c
+++ b/drivers/mfd/syscon.c
@@ -204,6 +204,27 @@ struct regmap *syscon_regmap_lookup_by_c
 }
 EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_compatible);
 
+static int syscon_match_pdevname(struct device *dev, const void *data)
+{
+	return !strcmp(dev_name(dev), (const char *)data);
+}
+
+struct regmap *syscon_regmap_lookup_by_pdevname(const char *s)
+{
+	struct device *dev;
+	struct syscon *syscon;
+
+	dev = driver_find_device(&syscon_driver.driver, NULL, (void *)s,
+				 syscon_match_pdevname);
+	if (!dev)
+		return ERR_PTR(-EPROBE_DEFER);
+
+	syscon = dev_get_drvdata(dev);
+
+	return syscon->regmap;
+}
+EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_pdevname);
+
 struct regmap *syscon_regmap_lookup_by_phandle(struct device_node *np,
 					const char *property)
 {
--- a/include/linux/mfd/syscon.h
+++ b/include/linux/mfd/syscon.h
@@ -20,6 +20,7 @@ struct device_node;
 extern struct regmap *device_node_to_regmap(struct device_node *np);
 extern struct regmap *syscon_node_to_regmap(struct device_node *np);
 extern struct regmap *syscon_regmap_lookup_by_compatible(const char *s);
+extern struct regmap *syscon_regmap_lookup_by_pdevname(const char *s);
 extern struct regmap *syscon_regmap_lookup_by_phandle(
 					struct device_node *np,
 					const char *property);
@@ -38,6 +39,11 @@ static inline struct regmap *syscon_regm
 {
 	return ERR_PTR(-ENOTSUPP);
 }
+
+static inline struct regmap *syscon_regmap_lookup_by_pdevname(const char *s)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
 
 static inline struct regmap *syscon_regmap_lookup_by_phandle(
 					struct device_node *np,