firmware/dmi_scan: Uninline dmi_get_bios_year() helper

Uninline dmi_get_bios_year() which, in particular, allows us
to optimize it in the future.

While doing this, convert the function to return an error code
when BIOS date is not present or not parsable, or CONFIG_DMI=n.

Additionally, during the move, add a bit of documentation.

Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rjw@rjwysocki.net>
Cc: linux-acpi@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Fixes: 492a1abd61 ("dmi: Introduce the dmi_get_bios_year() helper function")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

drivers/firmware/dmi_scan.c

@@ -1004,6 +1004,26 @@ out:
 }
 EXPORT_SYMBOL(dmi_get_date);
 
+/**
+ *	dmi_get_bios_year - get a year out of DMI_BIOS_DATE field
+ *
+ *	Returns year on success, -ENXIO if DMI is not selected,
+ *	or a different negative error code if DMI field is not present
+ *	or not parseable.
+ */
+int dmi_get_bios_year(void)
+{
+	bool exists;
+	int year;
+
+	exists = dmi_get_date(DMI_BIOS_DATE, &year, NULL, NULL);
+	if (!exists)
+		return -ENODATA;
+
+	return year ? year : -ERANGE;
+}
+EXPORT_SYMBOL(dmi_get_bios_year);
+
 /**
  *	dmi_walk - Walk the DMI table and get called back for every record
  *	@decode: Callback function

include/linux/dmi.h

@@ -106,6 +106,7 @@ extern void dmi_scan_machine(void);
 extern void dmi_memdev_walk(void);
 extern void dmi_set_dump_stack_arch_desc(void);
 extern bool dmi_get_date(int field, int *yearp, int *monthp, int *dayp);
+extern int dmi_get_bios_year(void);
 extern int dmi_name_in_vendors(const char *str);
 extern int dmi_name_in_serial(const char *str);
 extern int dmi_available;
@@ -133,6 +134,7 @@ static inline bool dmi_get_date(int field, int *yearp, int *monthp, int *dayp)
 		*dayp = 0;
 	return false;
 }
+static inline int dmi_get_bios_year(void) { return -ENXIO; }
 static inline int dmi_name_in_vendors(const char *s) { return 0; }
 static inline int dmi_name_in_serial(const char *s) { return 0; }
 #define dmi_available 0
@@ -147,13 +149,4 @@ static inline const struct dmi_system_id *
 
 #endif
 
-static inline int dmi_get_bios_year(void)
-{
-	int year;
-
-	dmi_get_date(DMI_BIOS_DATE, &year, NULL, NULL);
-
-	return year;
-}
-
 #endif	/* __DMI_H__ */