platform/x86: intel-vbtn: Do not advertise switches to userspace if they are not there

Commit de9647ef ("platform/x86: intel-vbtn: Only activate tablet mode
switch on 2-in-1's") added a DMI chassis-type check to avoid accidentally
reporting SW_TABLET_MODE = 1 to userspace on laptops (specifically on the
Dell XPS 9360), to avoid e.g. userspace ignoring touchpad events because
userspace thought the device was in tablet-mode.

But if we are not getting the initial status of the switch because the
device does not have a tablet mode, then we really should not advertise
the presence of a tablet-mode switch to userspace at all, as userspace may
use the mere presence of this switch for certain heuristics.

Fixes: de9647ef ("platform/x86: intel-vbtn: Only activate tablet mode switch on 2-in-1's")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/intel-vbtn.c

@@ -55,6 +55,7 @@ static const struct key_entry intel_vbtn_switchmap[] = {
 struct intel_vbtn_priv {
 	struct key_entry keymap[KEYMAP_LEN];
 	struct input_dev *input_dev;
+	bool has_switches;
 	bool wakeup_mode;
 };
 
@@ -70,7 +71,7 @@ static int intel_vbtn_input_setup(struct platform_device *device)
 		keymap_len += ARRAY_SIZE(intel_vbtn_keymap);
 	}
 
-	if (true) {
+	if (priv->has_switches) {
 		memcpy(&priv->keymap[keymap_len], intel_vbtn_switchmap,
 		       ARRAY_SIZE(intel_vbtn_switchmap) *
 		       sizeof(struct key_entry));
@@ -138,16 +139,12 @@ static void notify_handler(acpi_handle handle, u32 event, void *context)
 
 static void detect_tablet_mode(struct platform_device *device)
 {
-	const char *chassis_type = dmi_get_system_info(DMI_CHASSIS_TYPE);
 	struct intel_vbtn_priv *priv = dev_get_drvdata(&device->dev);
 	acpi_handle handle = ACPI_HANDLE(&device->dev);
 	unsigned long long vgbs;
 	acpi_status status;
 	int m;
 
-	if (!(chassis_type && strcmp(chassis_type, "31") == 0))
-		return;
-
 	status = acpi_evaluate_integer(handle, "VGBS", NULL, &vgbs);
 	if (ACPI_FAILURE(status))
 		return;
@@ -158,6 +155,19 @@ static void detect_tablet_mode(struct platform_device *device)
 	input_report_switch(priv->input_dev, SW_DOCK, m);
 }
 
+static bool intel_vbtn_has_switches(acpi_handle handle)
+{
+	const char *chassis_type = dmi_get_system_info(DMI_CHASSIS_TYPE);
+	unsigned long long vgbs;
+	acpi_status status;
+
+	if (!(chassis_type && strcmp(chassis_type, "31") == 0))
+		return false;
+
+	status = acpi_evaluate_integer(handle, "VGBS", NULL, &vgbs);
+	return ACPI_SUCCESS(status);
+}
+
 static int intel_vbtn_probe(struct platform_device *device)
 {
 	acpi_handle handle = ACPI_HANDLE(&device->dev);
@@ -176,13 +186,16 @@ static int intel_vbtn_probe(struct platform_device *device)
 		return -ENOMEM;
 	dev_set_drvdata(&device->dev, priv);
 
+	priv->has_switches = intel_vbtn_has_switches(handle);
+
 	err = intel_vbtn_input_setup(device);
 	if (err) {
 		pr_err("Failed to setup Intel Virtual Button\n");
 		return err;
 	}
 
-	detect_tablet_mode(device);
+	if (priv->has_switches)
+		detect_tablet_mode(device);
 
 	status = acpi_install_notify_handler(handle,
 					     ACPI_DEVICE_NOTIFY,