ACPI: thinkpad-acpi: improve thinkpad detection

Improve the detection of ThinkPads, so as to reduce the chances of false
positives.

Since this could potentially add false negatives on the very old models,
add a module parameter to force the detection of a thinkpad.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

Documentation/thinkpad-acpi.txt

@@ -716,3 +716,10 @@ to enable more than one output class, just add their values.
 
 There is also a kernel build option to enable more debugging
 information, which may be necessary to debug driver problems.
+
+Force loading of module
+-----------------------
+
+If thinkpad-acpi refuses to detect your ThinkPad, you can try to specify
+the module parameter force_load=1.  Regardless of whether this works or
+not, please contact ibm-acpi-devel@lists.sourceforge.net with a report.

drivers/misc/thinkpad_acpi.c

@@ -2881,6 +2881,16 @@ static int __init probe_for_thinkpad(void)
 		return -ENODEV;
 	}
 
+	/*
+	 * Risks a regression on very old machines, but reduces potential
+	 * false positives a damn great deal
+	 */
+	if (!is_thinkpad)
+		is_thinkpad = dmi_name_in_vendors("IBM");
+
+	if (!is_thinkpad && !force_load)
+		return -ENODEV;
+
 	return 0;
 }
 
@@ -2986,6 +2996,9 @@ module_param(experimental, int, 0);
 static u32 dbg_level;
 module_param_named(debug, dbg_level, uint, 0);
 
+static int force_load;
+module_param(force_load, int, 0);
+
 #define IBM_PARAM(feature) \
 	module_param_call(feature, set_ibm_param, NULL, NULL, 0)
 

drivers/misc/thinkpad_acpi.h

@@ -128,6 +128,7 @@ static char *next_cmd(char **cmds);
 /* Module */
 static int experimental;
 static u32 dbg_level;
+static int force_load;
 static char *ibm_thinkpad_ec_found;
 
 static char* check_dmi_for_ec(void);