[v6,1/1] serial: core: Start managing serial controllers to enable runtime PM

diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst
--- a/Documentation/firmware-guide/acpi/enumeration.rst
+++ b/Documentation/firmware-guide/acpi/enumeration.rst
@@ -19,9 +19,8 @@  possible we decided to do following:
     platform devices.
 
   - Devices behind real busses where there is a connector resource
-    are represented as struct spi_device or struct i2c_device. Note
-    that standard UARTs are not busses so there is no struct uart_device,
-    although some of them may be represented by struct serdev_device.
+    are represented as struct spi_device, struct i2c_device or
+    struct serdev_device.
 
 As both ACPI and Device Tree represent a tree of devices (and their
 resources) this implementation follows the Device Tree way as much as
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -996,6 +996,7 @@  int serial8250_register_8250_port(const struct uart_8250_port *up)
 		if (uart->port.dev)
 			uart_remove_one_port(&serial8250_reg, &uart->port);
 
+		uart->port.ctrl_id	= up->port.ctrl_id;
 		uart->port.iobase       = up->port.iobase;
 		uart->port.membase      = up->port.membase;
 		uart->port.irq          = up->port.irq;
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -3,7 +3,7 @@ 
 # Makefile for the kernel serial device drivers.
 #
 
-obj-$(CONFIG_SERIAL_CORE) += serial_core.o
+obj-$(CONFIG_SERIAL_CORE) += serial_base.o serial_core.o serial_ctrl.o serial_port.o
 
 obj-$(CONFIG_SERIAL_EARLYCON) += earlycon.o
 obj-$(CONFIG_SERIAL_EARLYCON_SEMIHOST) += earlycon-semihost.o
diff --git a/drivers/tty/serial/serial_base.c b/drivers/tty/serial/serial_base.c
new file mode 100644
--- /dev/null
+++ b/drivers/tty/serial/serial_base.c
@@ -0,0 +1,98 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * Serial core base layer for controllers
+ *
+ * The serial core bus manages the serial core controller instances.
+ */
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/serial_core.h>
+#include <linux/slab.h>
+
+#include "serial_base.h"
+
+static int serial_base_match(struct device *dev, struct device_driver *drv)
+{
+	int len = strlen(drv->name);
+
+	return (strncmp(dev_name(dev), drv->name, len) == 0);
+}
+
+static struct bus_type serial_base_bus_type = {
+	.name = "serial-base",
+	.match = serial_base_match,
+};
+
+int serial_base_driver_register(struct device_driver *driver)
+{
+	driver->bus = &serial_base_bus_type;
+
+	return driver_register(driver);
+}
+EXPORT_SYMBOL_GPL(serial_base_driver_register);
+
+void serial_base_driver_unregister(struct device_driver *driver)
+{
+	driver_unregister(driver);
+}
+EXPORT_SYMBOL_GPL(serial_base_driver_unregister);
+
+struct serial_base_device *serial_base_device_add(struct uart_port *port,
+						  const char *name,
+						  struct device *parent_dev)
+{
+	struct serial_base_device *dev;
+	int ret, id;
+
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev)
+		return NULL;
+
+	device_initialize(&dev->dev);
+	dev->dev.parent = parent_dev;
+	dev->dev.bus = &serial_base_bus_type;
+
+	if (!strncmp(name, "ctrl", 4)) {
+		id = port->ctrl_id;
+	} else {
+		id = port->line;
+		dev->port = port;
+	}
+
+	dev_set_name(&dev->dev, "%s.%s.%d", name, dev_name(port->dev), id);
+
+	ret = device_add(&dev->dev);
+	if (ret) {
+		kfree(dev);
+		return NULL;
+	}
+
+	return dev;
+}
+EXPORT_SYMBOL_GPL(serial_base_device_add);
+
+void serial_base_device_remove(struct serial_base_device *dev)
+{
+	device_del(&dev->dev);
+	kfree(dev);
+}
+EXPORT_SYMBOL_GPL(serial_base_device_remove);
+
+static int serial_base_init(void)
+{
+	return bus_register(&serial_base_bus_type);
+}
+
+static void serial_base_exit(void)
+{
+	bus_unregister(&serial_base_bus_type);
+}
+
+module_init(serial_base_init);
+module_exit(serial_base_exit);
+
+MODULE_AUTHOR("Tony Lindgren <tony@atomide.com>");
+MODULE_DESCRIPTION("Serial core bus");
+MODULE_LICENSE("GPL");
diff --git a/drivers/tty/serial/serial_base.h b/drivers/tty/serial/serial_base.h
new file mode 100644
--- /dev/null
+++ b/drivers/tty/serial/serial_base.h
@@ -0,0 +1,27 @@ 
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/* Serial core related functions, serial port device drivers do not need this. */
+
+struct device;
+struct uart_driver;
+struct uart_port;
+
+struct serial_base_device {
+	struct device dev;
+	struct uart_port *port;
+};
+
+#define to_serial_base_device(x) container_of((x), struct serial_base_device, dev)
+
+extern int serial_base_driver_register(struct device_driver *driver);
+extern void serial_base_driver_unregister(struct device_driver *driver);
+extern struct serial_base_device *serial_base_device_add(struct uart_port *port,
+							 const char *name,
+							 struct device *parent_dev);
+extern void serial_base_device_remove(struct serial_base_device *dev);
+
+extern int serial_ctrl_register_port(struct uart_driver *drv, struct uart_port *port);
+extern void serial_ctrl_unregister_port(struct uart_driver *drv, struct uart_port *port);
+
+extern int serial_core_register_port(struct uart_driver *drv, struct uart_port *port);
+extern void serial_core_unregister_port(struct uart_driver *drv, struct uart_port *port);
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -16,6 +16,7 @@ 
 #include <linux/console.h>
 #include <linux/gpio/consumer.h>
 #include <linux/of.h>
+#include <linux/pm_runtime.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/device.h>
@@ -30,6 +31,8 @@ 
 #include <linux/irq.h>
 #include <linux/uaccess.h>
 
+#include "serial_base.h"
+
 /*
  * This is used to lock changes in serial line configuration.
  */
@@ -136,9 +139,31 @@  static void __uart_start(struct tty_struct *tty)
 {
 	struct uart_state *state = tty->driver_data;
 	struct uart_port *port = state->uart_port;
+	struct device *port_dev;
+	int err;
+
+	if (!port || uart_tx_stopped(port))
+		return;
+
+	port_dev = port->port_dev;
+
+	err = pm_runtime_get(port_dev);
+	if (err < 0) {
+		/* Something went wrong, attempt to start TX anyways */
+		port->ops->start_tx(port);
+		pm_runtime_put_noidle(port_dev);
+		return;
+	}
 
-	if (port && !uart_tx_stopped(port))
+	/*
+	 * Start TX if enabled, and kick runtime PM. Otherwise we must
+	 * wait for a retry. See also serial_port.c for runtime PM
+	 * autosuspend timeout.
+	 */
+	if (pm_runtime_active(port_dev))
 		port->ops->start_tx(port);
+	pm_runtime_mark_last_busy(port_dev);
+	pm_runtime_put_autosuspend(port_dev);
 }
 
 static void uart_start(struct tty_struct *tty)
@@ -3039,7 +3064,7 @@  static const struct attribute_group tty_dev_attr_group = {
 };
 
 /**
- * uart_add_one_port - attach a driver-defined port structure
+ * serial_core_add_one_port - attach a driver-defined port structure
  * @drv: pointer to the uart low level driver structure for this port
  * @uport: uart port structure to use for this port.
  *
@@ -3049,7 +3074,7 @@  static const struct attribute_group tty_dev_attr_group = {
  * core driver. The main purpose is to allow the low level uart drivers to
  * expand uart_port, rather than having yet more levels of structures.
  */
-int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
+static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 {
 	struct uart_state *state;
 	struct tty_port *port;
@@ -3139,10 +3164,9 @@  int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 
 	return ret;
 }
-EXPORT_SYMBOL(uart_add_one_port);
 
 /**
- * uart_remove_one_port - detach a driver defined port structure
+ * serial_core_remove_one_port - detach a driver defined port structure
  * @drv: pointer to the uart low level driver structure for this port
  * @uport: uart port structure for this port
  *
@@ -3151,7 +3175,8 @@  EXPORT_SYMBOL(uart_add_one_port);
  * This unhooks (and hangs up) the specified port structure from the core
  * driver. No further calls will be made to the low-level code for this port.
  */
-int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
+static int serial_core_remove_one_port(struct uart_driver *drv,
+				       struct uart_port *uport)
 {
 	struct uart_state *state = drv->state + uport->line;
 	struct tty_port *port = &state->port;
@@ -3208,6 +3233,8 @@  int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
 	 * Indicate that there isn't a port here anymore.
 	 */
 	uport->type = PORT_UNKNOWN;
+	uport->port_dev = NULL;
+	uport->ctrl_id = -ENODEV;
 
 	mutex_lock(&port->mutex);
 	WARN_ON(atomic_dec_return(&state->refcount) < 0);
@@ -3219,7 +3246,6 @@  int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
 
 	return ret;
 }
-EXPORT_SYMBOL(uart_remove_one_port);
 
 /**
  * uart_match_port - are the two ports equivalent?
@@ -3254,6 +3280,142 @@  bool uart_match_port(const struct uart_port *port1,
 }
 EXPORT_SYMBOL(uart_match_port);
 
+/*
+ * Find a registered serial core controller device if one exists. Returns
+ * the first device matching the ctrl_id. Caller must hold port_mutex.
+ */
+static struct device *serial_core_ctrl_find(struct uart_driver *drv,
+					    struct device *phys_dev,
+					    int ctrl_id)
+{
+	struct uart_state *state;
+	int i;
+
+	if (ctrl_id < 0)
+		return NULL;
+
+	lockdep_assert_held(&port_mutex);
+
+	for (i = 0; i < drv->nr; i++) {
+		state = drv->state + i;
+		if (!state->uart_port || !state->uart_port->port_dev)
+			continue;
+
+		if (state->uart_port->dev == phys_dev &&
+		    state->uart_port->ctrl_id == ctrl_id)
+			return state->uart_port->port_dev->parent;
+	}
+
+	return NULL;
+}
+
+static struct device *serial_core_ctrl_device_add(struct uart_port *port)
+{
+	struct serial_base_device *dev;
+
+	dev = serial_base_device_add(port, "ctrl", port->dev);
+	if (IS_ERR(dev))
+		return NULL;
+
+	return &dev->dev;
+}
+
+static int serial_core_port_device_add(struct device *ctrl_dev, struct uart_port *port)
+{
+	struct serial_base_device *dev;
+
+	dev = serial_base_device_add(port, "port", ctrl_dev);
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+
+	port->port_dev = &dev->dev;
+
+	return 0;
+}
+
+static void serial_core_port_device_remove(struct device *port_dev)
+{
+	struct serial_base_device *dev = to_serial_base_device(port_dev);
+
+	serial_base_device_remove(dev);
+}
+
+/*
+ * Initialize a serial core port device, and a controller device if needed.
+ */
+int serial_core_register_port(struct uart_driver *drv, struct uart_port *port)
+{
+	struct device *ctrl_dev;
+	bool added = false;
+	int ret;
+
+	mutex_lock(&port_mutex);
+
+	/* Inititalize a serial core controller device if needed */
+	ctrl_dev = serial_core_ctrl_find(drv, port->dev, port->ctrl_id);
+	if (!ctrl_dev) {
+		ctrl_dev = serial_core_ctrl_device_add(port);
+		if (!ctrl_dev) {
+			ret = -ENODEV;
+			goto err_unlock;
+		}
+		added = true;
+	}
+
+	/* Initialize a serial core port device */
+	ret = serial_core_port_device_add(ctrl_dev, port);
+	if (ret)
+		goto err_unregister_ctrl_dev;
+
+	mutex_unlock(&port_mutex);
+
+	ret = serial_core_add_one_port(drv, port);
+	if (ret)
+		goto err_unregister_port_dev;
+
+	return 0;
+
+err_unregister_port_dev:
+	mutex_lock(&port_mutex);
+	serial_core_port_device_remove(port->port_dev);
+
+err_unregister_ctrl_dev:
+	if (added)
+		serial_base_device_remove(to_serial_base_device(ctrl_dev));
+
+err_unlock:
+	mutex_unlock(&port_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_NS(serial_core_register_port, SERIAL_CORE);
+
+/*
+ * Removes a serial core port device, and the related serial core controller
+ * device if the last instance.
+ */
+void serial_core_unregister_port(struct uart_driver *drv, struct uart_port *port)
+{
+	struct device *phys_dev = port->dev;
+	struct device *port_dev = port->port_dev;
+	struct device *ctrl_dev = port_dev->parent;
+	int ctrl_id = port->ctrl_id;
+
+	serial_core_remove_one_port(drv, port);
+
+	mutex_lock(&port_mutex);
+
+	/* Note that struct uart_port *port is no longer valid at this point */
+	serial_core_port_device_remove(port_dev);
+
+	/* Drop the serial core controller device if no ports are using it */
+	if (!serial_core_ctrl_find(drv, phys_dev, ctrl_id))
+		serial_base_device_remove(to_serial_base_device(ctrl_dev));
+
+	mutex_unlock(&port_mutex);
+}
+EXPORT_SYMBOL_NS(serial_core_unregister_port, SERIAL_CORE);
+
 /**
  * uart_handle_dcd_change - handle a change of carrier detect state
  * @uport: uart_port structure for the open port
diff --git a/drivers/tty/serial/serial_ctrl.c b/drivers/tty/serial/serial_ctrl.c
new file mode 100644
--- /dev/null
+++ b/drivers/tty/serial/serial_ctrl.c
@@ -0,0 +1,72 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * Serial core controller driver
+ *
+ * This driver manages the serial core controller struct device instances.
+ * The serial core controller devices are children of the physical serial
+ * port device.
+ */
+
+#include <linux/module.h>
+#include <linux/pm_runtime.h>
+#include <linux/serial_core.h>
+
+#include "serial_base.h"
+
+static DEFINE_RUNTIME_DEV_PM_OPS(serial_ctrl_pm, NULL, NULL, NULL);
+
+static int serial_ctrl_probe(struct device *dev)
+{
+	pm_runtime_enable(dev);
+
+	return 0;
+}
+
+static int serial_ctrl_remove(struct device *dev)
+{
+	pm_runtime_disable(dev);
+
+	return 0;
+}
+
+/*
+ * Serial core controller device init functions. Note that the physical
+ * serial port device driver may not have completed probe at this point.
+ */
+int serial_ctrl_register_port(struct uart_driver *drv, struct uart_port *port)
+{
+	return serial_core_register_port(drv, port);
+}
+EXPORT_SYMBOL_NS(serial_ctrl_register_port, SERIAL_CORE);
+
+void serial_ctrl_unregister_port(struct uart_driver *drv, struct uart_port *port)
+{
+	serial_core_unregister_port(drv, port);
+}
+EXPORT_SYMBOL_NS(serial_ctrl_unregister_port, SERIAL_CORE);
+
+static struct device_driver serial_ctrl_driver = {
+	.name = "ctrl",
+	.suppress_bind_attrs = true,
+	.probe = serial_ctrl_probe,
+	.remove = serial_ctrl_remove,
+};
+
+static int serial_ctrl_init(void)
+{
+	return serial_base_driver_register(&serial_ctrl_driver);
+}
+
+static void serial_ctrl_exit(void)
+{
+	serial_base_driver_unregister(&serial_ctrl_driver);
+}
+
+module_init(serial_ctrl_init);
+module_exit(serial_ctrl_exit);
+
+MODULE_AUTHOR("Tony Lindgren <tony@atomide.com>");
+MODULE_DESCRIPTION("Serial core controller driver");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS(SERIAL_CORE);
diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c
new file mode 100644
--- /dev/null
+++ b/drivers/tty/serial/serial_port.c
@@ -0,0 +1,101 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * Serial core port device driver
+ */
+
+#include <linux/module.h>
+#include <linux/pm_runtime.h>
+#include <linux/serial_core.h>
+
+#include "serial_base.h"
+
+#define SERIAL_PORT_AUTOSUSPEND_DELAY_MS	500
+
+/* Only considers pending TX for now. Caller must take care of locking */
+static int __serial_port_busy(struct uart_port *port)
+{
+	return !uart_tx_stopped(port) &&
+		uart_circ_chars_pending(&port->state->xmit);
+}
+
+static int serial_port_runtime_resume(struct device *dev)
+{
+	struct serial_base_device *scd = to_serial_base_device(dev);
+	struct uart_port *port = scd->port;
+	unsigned long flags;
+
+	/* Flush any pending TX for the port */
+	spin_lock_irqsave(&port->lock, flags);
+	if (__serial_port_busy(port))
+		port->ops->start_tx(port);
+	spin_unlock_irqrestore(&port->lock, flags);
+	pm_runtime_mark_last_busy(dev);
+
+	return 0;
+}
+
+static DEFINE_RUNTIME_DEV_PM_OPS(serial_port_pm, NULL,
+				 serial_port_runtime_resume,
+				 NULL);
+
+static int serial_port_probe(struct device *dev)
+{
+	pm_runtime_enable(dev);
+	pm_runtime_set_autosuspend_delay(dev, SERIAL_PORT_AUTOSUSPEND_DELAY_MS);
+	pm_runtime_use_autosuspend(dev);
+
+	return 0;
+}
+
+static int serial_port_remove(struct device *dev)
+{
+	pm_runtime_dont_use_autosuspend(dev);
+	pm_runtime_disable(dev);
+
+	return 0;
+}
+
+/*
+ * Serial core port device init functions. Note that the physical serial
+ * port device driver may not have completed probe at this point.
+ */
+int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
+{
+	return serial_ctrl_register_port(drv, port);
+}
+EXPORT_SYMBOL(uart_add_one_port);
+
+int uart_remove_one_port(struct uart_driver *drv, struct uart_port *port)
+{
+	serial_ctrl_unregister_port(drv, port);
+
+	return 0;
+}
+EXPORT_SYMBOL(uart_remove_one_port);
+
+static struct device_driver serial_port_driver = {
+	.name = "port",
+	.suppress_bind_attrs = true,
+	.probe = serial_port_probe,
+	.remove = serial_port_remove,
+	.pm = pm_ptr(&serial_port_pm),
+};
+
+static int serial_port_init(void)
+{
+	return serial_base_driver_register(&serial_port_driver);
+}
+
+static void serial_port_exit(void)
+{
+	serial_base_driver_unregister(&serial_port_driver);
+}
+
+module_init(serial_port_init);
+module_exit(serial_port_exit);
+
+MODULE_AUTHOR("Tony Lindgren <tony@atomide.com>");
+MODULE_DESCRIPTION("Serial controller port driver");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS(SERIAL_CORE);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -458,6 +458,7 @@  struct uart_port {
 						struct serial_rs485 *rs485);
 	int			(*iso7816_config)(struct uart_port *,
 						  struct serial_iso7816 *iso7816);
+	int			ctrl_id;		/* optional serial core controller id */
 	unsigned int		irq;			/* irq number */
 	unsigned long		irqflags;		/* irq flags  */
 	unsigned int		uartclk;		/* base uart clock */
@@ -563,7 +564,8 @@  struct uart_port {
 	unsigned int		minor;
 	resource_size_t		mapbase;		/* for ioremap */
 	resource_size_t		mapsize;
-	struct device		*dev;			/* parent device */
+	struct device		*dev;			/* serial port physical parent device */
+	struct device		*port_dev;		/* serial core port device */
 
 	unsigned long		sysrq;			/* sysrq timeout */
 	unsigned int		sysrq_ch;		/* char for sysrq */