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: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Matt Domsch <Matt_Domsch@dell.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 19 insertions, 3 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 5afc21b20a9..3ce193f8656 100644
--- a/Documentation/kernel-parameters.txt
+++ b/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.
diff --git a/arch/x86/boot/edd.c b/arch/x86/boot/edd.c
index d84a48ece78..03399d64013 100644
--- a/arch/x86/boot/edd.c
+++ b/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");
diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 40ffd767647..dc2cec6127d 100644
--- a/drivers/firmware/Kconfig
+++ b/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