platform/x86: nvidia-wmi-ec-backlight: Add force module parameter

On some Lenovo Legion models, the backlight might be driven by either
one of nvidia_wmi_ec_backlight or amdgpu_bl0 at different times.

When the Nvidia WMI EC backlight interface reports the backlight is
controlled by the EC, the current backlight handling only registers
nvidia_wmi_ec_backlight (and registers no other backlight interfaces).

This hides (never registers) the amdgpu_bl0 interface, where as prior
to 6.1.4 users would have both nvidia_wmi_ec_backlight and amdgpu_bl0
and could work around things in userspace.

Add a force module parameter which can be used with acpi_backlight=native
to restore the old behavior as a workound (for now) by passing:

"acpi_backlight=native nvidia-wmi-ec-backlight.force=1"

Fixes: 8d0ca287 ("platform/x86: nvidia-wmi-ec-backlight: Use acpi_video_get_backlight_type()")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217026
Cc: stable@vger.kernel.org
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Daniel Dadap <ddadap@nvidia.com>
Link: https://lore.kernel.org/r/20230217144208.5721-1-hdegoede@redhat.com

drivers/platform/x86/nvidia-wmi-ec-backlight.c

@@ -12,6 +12,10 @@
 #include <linux/wmi.h>
 #include <acpi/video.h>
 
+static bool force;
+module_param(force, bool, 0444);
+MODULE_PARM_DESC(force, "Force loading (disable acpi_backlight=xxx checks");
+
 /**
  * wmi_brightness_notify() - helper function for calling WMI-wrapped ACPI method
  * @w:    Pointer to the struct wmi_device identified by %WMI_BRIGHTNESS_GUID
@@ -91,7 +95,7 @@ static int nvidia_wmi_ec_backlight_probe(struct wmi_device *wdev, const void *ct
 	int ret;
 
 	/* drivers/acpi/video_detect.c also checks that SOURCE == EC */
-	if (acpi_video_get_backlight_type() != acpi_backlight_nvidia_wmi_ec)
+	if (!force && acpi_video_get_backlight_type() != acpi_backlight_nvidia_wmi_ec)
 		return -ENODEV;
 
 	/*