platform/x86: think-lmi: only display possible_values if available

Some attributes don't have any values available. In those cases don't
make the possible_values entry visible.

Fixes: a40cd7ef22 ("platform/x86: think-lmi: Add WMI interface support on Lenovo platforms")
Signed-off-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Link: https://lore.kernel.org/r/20230320003221.561750-3-mpearson-lenovo@squebb.ca
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/think-lmi.c

@@ -941,9 +941,6 @@ static ssize_t possible_values_show(struct kobject *kobj, struct kobj_attribute
 {
 	struct tlmi_attr_setting *setting = to_tlmi_attr_setting(kobj);
 
-	if (!tlmi_priv.can_get_bios_selections)
-		return -EOPNOTSUPP;
-
 	return sysfs_emit(buf, "%s\n", setting->possible_values);
 }
 
@@ -1052,6 +1049,18 @@ static struct kobj_attribute attr_current_val = __ATTR_RW_MODE(current_value, 06
 
 static struct kobj_attribute attr_type = __ATTR_RO(type);
 
+static umode_t attr_is_visible(struct kobject *kobj,
+					     struct attribute *attr, int n)
+{
+	struct tlmi_attr_setting *setting = to_tlmi_attr_setting(kobj);
+
+	/* We don't want to display possible_values attributes if not available */
+	if ((attr == &attr_possible_values.attr) && (!setting->possible_values))
+		return 0;
+
+	return attr->mode;
+}
+
 static struct attribute *tlmi_attrs[] = {
 	&attr_displ_name.attr,
 	&attr_current_val.attr,
@@ -1061,6 +1070,7 @@ static struct attribute *tlmi_attrs[] = {
 };
 
 static const struct attribute_group tlmi_attr_group = {
+	.is_visible = attr_is_visible,
 	.attrs = tlmi_attrs,
 };