edd: add default mode CONFIG_EDD_OFF=n, override with edd={on,off}

Add a kernel parameter option to 'edd' to enable/disable BIOS Enhanced Disk
Drive Services.  CONFIG_EDD_OFF disables EDD while still compiling EDD into
the kernel.  Default behavior can be forced using 'edd=on' or 'edd=off' as
a kernel parameter.

[akpm@linux-foundation.org: fix kernel-parameters.txt]
Signed-off-by: NTim Gardner <tim.gardner@canonical.com>
Signed-off-by: NMatt Domsch <Matt_Domsch@dell.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/kernel-parameters.txt

@@ -627,8 +627,7 @@ and is between 256 and 4096 characters. It is defined in the file
 	eata=		[HW,SCSI]
 
 	edd=		[EDD]
-			Format: {"of[f]" | "sk[ipmbr]"}
-			See comment in arch/i386/boot/edd.S
+			Format: {"off" | "on" | "skip[mbr]"}
 
 	eisa_irq_edge=	[PARISC,HW]
 			See header of drivers/parisc/eisa.c.

arch/x86/boot/edd.c

@@ -126,17 +126,25 @@ void query_edd(void)
 {
 	char eddarg[8];
 	int do_mbr = 1;
+#ifdef CONFIG_EDD_OFF
+	int do_edd = 0;
+#else
 	int do_edd = 1;
+#endif
 	int be_quiet;
 	int devno;
 	struct edd_info ei, *edp;
 	u32 *mbrptr;
 
 	if (cmdline_find_option("edd", eddarg, sizeof eddarg) > 0) {
-		if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip"))
+		if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip")) {
+			do_edd = 1;
 			do_mbr = 0;
+		}
 		else if (!strcmp(eddarg, "off"))
 			do_edd = 0;
+		else if (!strcmp(eddarg, "on"))
+			do_edd = 1;
 	}
 
 	be_quiet = cmdline_find_option_bool("quiet");

drivers/firmware/Kconfig

@@ -17,6 +17,15 @@ config EDD
           obscure configurations. Most disk controller BIOS vendors do
           not yet implement this feature.
 
+config EDD_OFF
+	bool "Sets default behavior for EDD detection to off"
+	depends on EDD
+	default n
+	help
+	  Say Y if you want EDD disabled by default, even though it is compiled into the
+	  kernel. Say N if you want EDD enabled by default. EDD can be dynamically set
+	  using the kernel parameter 'edd={on|skipmbr|off}'.
+
 config EFI_VARS
 	tristate "EFI Variable Support via sysfs"
 	depends on EFI