debugfs: Add debugfs_create_xul() for hexadecimal unsigned long

The existing debugfs_create_ulong() function supports objects of
type "unsigned long", which are 32-bit or 64-bit depending on the
platform, in decimal form.  To format objects in hexadecimal, various
debugfs_create_x*() functions exist, but all of them take fixed-size
types.

Add a debugfs helper for "unsigned long" objects in hexadecimal format.
This avoids the need for users to open-code the same, or introduce
bugs when casting the value pointer to "u32 *" or "u64 *" to call
debugfs_create_x{32,64}().
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20191025094130.26033-2-geert+renesas@glider.beSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/filesystems/debugfs.txt

@@ -102,11 +102,14 @@ functions meant to help out in such special cases:
 As might be expected, this function will create a debugfs file to represent
 a variable of type size_t.
 
-Similarly, there is a helper for variables of type unsigned long:
+Similarly, there are helpers for variables of type unsigned long, in decimal
+and hexadecimal:
 
     struct dentry *debugfs_create_ulong(const char *name, umode_t mode,
 					struct dentry *parent,
 					unsigned long *value);
+    void debugfs_create_xul(const char *name, umode_t mode,
+			    struct dentry *parent, unsigned long *value);
 
 Boolean values can be placed in debugfs with:
 

include/linux/debugfs.h

@@ -351,4 +351,25 @@ static inline ssize_t debugfs_write_file_bool(struct file *file,
 
 #endif
 
+/**
+ * debugfs_create_xul - create a debugfs file that is used to read and write an
+ * unsigned long value, formatted in hexadecimal
+ * @name: a pointer to a string containing the name of the file to create.
+ * @mode: the permission that the file should have
+ * @parent: a pointer to the parent dentry for this file.  This should be a
+ *          directory dentry if set.  If this parameter is %NULL, then the
+ *          file will be created in the root of the debugfs filesystem.
+ * @value: a pointer to the variable that the file should read to and write
+ *         from.
+ */
+static inline void debugfs_create_xul(const char *name, umode_t mode,
+				      struct dentry *parent,
+				      unsigned long *value)
+{
+	if (sizeof(*value) == sizeof(u32))
+		debugfs_create_x32(name, mode, parent, (u32 *)value);
+	else
+		debugfs_create_x64(name, mode, parent, (u64 *)value);
+}
+
 #endif