devres: provide devm_kmemdup_const()

Provide a function similar to devm_strdup_const() but for copying blocks
of memory that are likely to be placed in .rodata.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/base/devres.c

@@ -1117,6 +1117,27 @@ void *devm_kmemdup(struct device *dev, const void *src, size_t len, gfp_t gfp)
 }
 EXPORT_SYMBOL_GPL(devm_kmemdup);
 
+/**
+ * devm_kmemdup_const - conditionally duplicate and manage a region of memory
+ *
+ * @dev: Device this memory belongs to
+ * @src: memory region to duplicate
+ * @len: memory region length,
+ * @gfp: GFP mask to use
+ *
+ * Return: source address if it is in .rodata or the return value of kmemdup()
+ * to which the function falls back otherwise.
+ */
+const void *
+devm_kmemdup_const(struct device *dev, const void *src, size_t len, gfp_t gfp)
+{
+	if (is_kernel_rodata((unsigned long)src))
+		return src;
+
+	return devm_kmemdup(dev, src, len, gfp);
+}
+EXPORT_SYMBOL_GPL(devm_kmemdup_const);
+
 struct pages_devres {
 	unsigned long addr;
 	unsigned int order;

include/linux/device/devres.h

@@ -80,6 +80,8 @@ void devm_kfree(struct device *dev, const void *p);
 
 void * __realloc_size(3)
 devm_kmemdup(struct device *dev, const void *src, size_t len, gfp_t gfp);
+const void *
+devm_kmemdup_const(struct device *dev, const void *src, size_t len, gfp_t gfp);
 static inline void *devm_kmemdup_array(struct device *dev, const void *src,
 				       size_t n, size_t size, gfp_t flags)
 {