ipmi: Turn off default probing of interfaces

The default probing can cause problems with some system, slow booting,
extra CPU usages, etc.  Turn it off by default and give a config option
to enable it.

From: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/ipmi/Kconfig

@@ -50,6 +50,18 @@ config IPMI_SI
 	 Currently, only KCS and SMIC are supported.  If
 	 you are using IPMI, you should probably say "y" here.
 
+config IPMI_SI_PROBE_DEFAULTS
+       bool 'Probe for all possible IPMI system interfaces by default'
+       default n
+       depends on IPMI_SI
+       help
+	 Modern systems will usually expose IPMI interfaces via a discoverable
+	 firmware mechanism such as ACPI or DMI. Older systems do not, and so
+	 the driver is forced to probe hardware manually. This may cause boot
+	 delays. Say "n" here to disable this manual probing. IPMI will then
+	 only be available on older systems if the "ipmi_si_intf.trydefaults=1"
+	 boot argument is passed.
+
 config IPMI_WATCHDOG
        tristate 'IPMI Watchdog Timer'
        help

drivers/char/ipmi/ipmi_si_intf.c

@@ -1239,7 +1239,7 @@ static bool          si_tryplatform = 1;
 #ifdef CONFIG_PCI
 static bool          si_trypci = 1;
 #endif
-static bool          si_trydefaults = 1;
+static bool          si_trydefaults = IS_ENABLED(CONFIG_IPMI_SI_PROBE_DEFAULTS);
 static char          *si_type[SI_MAX_PARMS];
 #define MAX_SI_TYPE_STR 30
 static char          si_type_str[MAX_SI_TYPE_STR];