platform/x86: acer-wmi: Add new force_caps module parameter

Add a new force_caps module parameter to allow overriding the drivers
builtin capability detection mechanism.

This can be used to for example:
-Disable rfkill functionality on devices where there is an AA OEM DMI
 record advertising non functional rfkill switches
-Force loading of the driver on devices with a missing AA OEM DMI record

Note that force_caps is -1 when unset, this allows forcing the
capability field to 0, which results in acer-wmi only providing WMI
hotkey handling while disabling all other (led, rfkill, backlight)
functionality.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20201019185628.264473-4-hdegoede@redhat.com

drivers/platform/x86/acer-wmi.c

@@ -232,6 +232,7 @@ static int mailled = -1;
 static int brightness = -1;
 static int threeg = -1;
 static int force_series;
+static int force_caps = -1;
 static bool ec_raw_mode;
 static bool has_type_aa;
 static u16 commun_func_bitmap;
@@ -241,11 +242,13 @@ module_param(mailled, int, 0444);
 module_param(brightness, int, 0444);
 module_param(threeg, int, 0444);
 module_param(force_series, int, 0444);
+module_param(force_caps, int, 0444);
 module_param(ec_raw_mode, bool, 0444);
 MODULE_PARM_DESC(mailled, "Set initial state of Mail LED");
 MODULE_PARM_DESC(brightness, "Set initial LCD backlight brightness");
 MODULE_PARM_DESC(threeg, "Set initial state of 3G hardware");
 MODULE_PARM_DESC(force_series, "Force a different laptop series");
+MODULE_PARM_DESC(force_caps, "Force the capability bitmask to this value");
 MODULE_PARM_DESC(ec_raw_mode, "Enable EC raw mode");
 
 struct acer_data {
@@ -2162,7 +2165,7 @@ static int __init acer_wmi_init(void)
 		}
 		/* WMID always provides brightness methods */
 		interface->capability |= ACER_CAP_BRIGHTNESS;
-	} else if (!wmi_has_guid(WMID_GUID2) && interface && !has_type_aa) {
+	} else if (!wmi_has_guid(WMID_GUID2) && interface && !has_type_aa && force_caps == -1) {
 		pr_err("No WMID device detection method found\n");
 		return -ENODEV;
 	}
@@ -2192,6 +2195,9 @@ static int __init acer_wmi_init(void)
 	if (acpi_video_get_backlight_type() != acpi_backlight_vendor)
 		interface->capability &= ~ACER_CAP_BRIGHTNESS;
 
+	if (force_caps != -1)
+		interface->capability = force_caps;
+
 	if (wmi_has_guid(WMID_GUID3)) {
 		if (ACPI_FAILURE(acer_wmi_enable_rf_button()))
 			pr_warn("Cannot enable RF Button Driver\n");