ANDROID: serdev: restrict claim of platform devices

Make the fallback path for claiming platform devices trigger only if a
new module parameter is specified:

  serdev_ttyport.pdev_tty_port=ttyS2

Bug: 146517987
Change-Id: Ibf331ad6e6d8712a405921530f217f7122428b13
Signed-off-by: Alistair Delva <adelva@google.com>

drivers/tty/serdev/core.c

@@ -623,16 +623,18 @@ static int platform_serdev_register_devices(struct serdev_controller *ctrl)
 	return err;
 }
 
+
 /**
- * serdev_controller_add() - Add an serdev controller
+ * serdev_controller_add_platform() - Add an serdev controller
  * @ctrl:	controller to be registered.
+ * @platform:	whether to permit fallthrough to platform device probe
  *
  * Register a controller previously allocated via serdev_controller_alloc() with
- * the serdev core.
+ * the serdev core. Optionally permit probing via a platform device fallback.
  */
-int serdev_controller_add(struct serdev_controller *ctrl)
+int serdev_controller_add_platform(struct serdev_controller *ctrl, bool platform)
 {
-	int ret_of, ret_acpi, ret_platform, ret;
+	int ret, ret_of, ret_acpi, ret_platform = -ENODEV;
 
 	/* Can't register until after driver model init */
 	if (WARN_ON(!is_registered))
@@ -646,6 +648,7 @@ int serdev_controller_add(struct serdev_controller *ctrl)
 
 	ret_of = of_serdev_register_devices(ctrl);
 	ret_acpi = acpi_serdev_register_devices(ctrl);
+	if (platform)
 		ret_platform = platform_serdev_register_devices(ctrl);
 	if (ret_of && ret_acpi && ret_platform) {
 		dev_dbg(&ctrl->dev, "no devices registered: of:%d acpi:%d "
@@ -664,7 +667,7 @@ int serdev_controller_add(struct serdev_controller *ctrl)
 	device_del(&ctrl->dev);
 	return ret;
 };
-EXPORT_SYMBOL_GPL(serdev_controller_add);
+EXPORT_SYMBOL_GPL(serdev_controller_add_platform);
 
 /* Remove a device associated with a controller */
 static int serdev_remove_device(struct device *dev, void *data)

drivers/tty/serdev/serdev-ttyport.c

@@ -7,9 +7,15 @@
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
 #include <linux/poll.h>
+#include <linux/platform_device.h>
+#include <linux/module.h>
 
 #define SERPORT_ACTIVE		1
 
+static char *pdev_tty_port;
+module_param(pdev_tty_port, charp, 0644);
+MODULE_PARM_DESC(pdev_tty_port, "platform device tty port to claim");
+
 struct serport {
 	struct tty_port *port;
 	struct tty_struct *tty;
@@ -267,6 +273,7 @@ struct device *serdev_tty_port_register(struct tty_port *port,
 {
 	struct serdev_controller *ctrl;
 	struct serport *serport;
+	bool platform = false;
 	int ret;
 
 	if (!port || !drv || !parent)
@@ -291,7 +298,24 @@ struct device *serdev_tty_port_register(struct tty_port *port,
 	port->client_ops = &client_ops;
 	port->client_data = ctrl;
 
-	ret = serdev_controller_add(ctrl);
+	/* There is not always a way to bind specific platform devices because
+	 * they may be defined on platforms without DT or ACPI. When dealing
+	 * with a platform devices, do not allow direct binding unless it is
+	 * whitelisted by module parameter. If a platform device is otherwise
+	 * described by DT or ACPI it will still be bound and this check will
+	 * be ignored.
+	 */
+	if (parent->bus == &platform_bus_type) {
+		char tty_port_name[7];
+
+		sprintf(tty_port_name, "%s%d", drv->name, idx);
+		if (pdev_tty_port &&
+		    !strcmp(pdev_tty_port, tty_port_name)) {
+			platform = true;
+		}
+	}
+
+	ret = serdev_controller_add_platform(ctrl, platform);
 	if (ret)
 		goto err_reset_data;
 

include/linux/serdev.h

@@ -173,9 +173,21 @@ int serdev_device_add(struct serdev_device *);
 void serdev_device_remove(struct serdev_device *);
 
 struct serdev_controller *serdev_controller_alloc(struct device *, size_t);
-int serdev_controller_add(struct serdev_controller *);
+int serdev_controller_add_platform(struct serdev_controller *, bool);
 void serdev_controller_remove(struct serdev_controller *);
 
+/**
+ * serdev_controller_add() - Add an serdev controller
+ * @ctrl:	controller to be registered.
+ *
+ * Register a controller previously allocated via serdev_controller_alloc() with
+ * the serdev core.
+ */
+static inline int serdev_controller_add(struct serdev_controller *ctrl)
+{
+	return serdev_controller_add_platform(ctrl, false);
+}
+
 static inline void serdev_controller_write_wakeup(struct serdev_controller *ctrl)
 {
 	struct serdev_device *serdev = ctrl->serdev;