[PATCH] x86_64: Clean up and tweak ACPI blacklist year code

- Move the core parser into dmi_scan.c. It can be useful for other
subsystems too.
- Differentiate between field doesn't exist and field is 0 or
unparseable. The first case is likely an old BIOS with broken ACPI,
the later is likely a slightly buggy BIOS where someone forget to
edit the date. Don't blacklist in the later case.

Signed-off-by: Andi Kleen <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/i386/kernel/dmi_scan.c

···
 	return NULL;
 }
 EXPORT_SYMBOL(dmi_find_device);
+
+/**
+ *	dmi_get_year - Return year of a DMI date
+ *	@field:	data index (like dmi_get_system_info)
+ *
+ *	Returns -1 when the field doesn't exist. 0 when it is broken.
+ */
+int dmi_get_year(int field)
+{
+	int year;
+	char *s = dmi_get_system_info(field);
+
+	if (!s)
+		return -1;
+	if (*s == '\0')
+		return 0;
+	s = strrchr(s, '/');
+	if (!s)
+		return 0;
+
+	s += 1;
+	year = simple_strtoul(s, NULL, 0);
+	if (year && year < 100) {	/* 2-digit year */
+		year += 1900;
+		if (year < 1996)	/* no dates < spec 1.0 */
+			year += 100;
+	}
+
+	return year;
+}

drivers/acpi/blacklist.c

···
 
 static int __init blacklist_by_year(void)
 {
-	int year;
-	char *s = dmi_get_system_info(DMI_BIOS_DATE);
-
-	if (!s)
+	int year = dmi_get_year(DMI_BIOS_DATE);
+	/* Doesn't exist? Likely an old system */
+	if (year == -1) 
+		return 1;
+	/* 0? Likely a buggy new BIOS */
+	if (year == 0)
 		return 0;
-	if (!*s)
-		return 0;
-
-	s = strrchr(s, '/');
-	if (!s)
-		return 0;
-
-	s += 1;
-
-	year = simple_strtoul(s, NULL, 0);
-
-	if (year < 100) {	/* 2-digit year */
-		year += 1900;
-		if (year < 1996)	/* no dates < spec 1.0 */
-			year += 100;
-	}
-
 	if (year < CONFIG_ACPI_BLACKLIST_YEAR) {
 		printk(KERN_ERR PREFIX "BIOS age (%d) fails cutoff (%d), "
 		       "acpi=force is required to enable ACPI\n",

include/linux/dmi.h

···
 extern struct dmi_device * dmi_find_device(int type, const char *name,
 	struct dmi_device *from);
 extern void dmi_scan_machine(void);
+extern int dmi_get_year(int field);
 
 #else
 
···
 static inline char * dmi_get_system_info(int field) { return NULL; }
 static inline struct dmi_device * dmi_find_device(int type, const char *name,
 	struct dmi_device *from) { return NULL; }
+static inline int dmi_get_year(int year) { return 0; }
 
 #endif