serial: core: Start managing serial controllers to enable runtime PM

We want to enable runtime PM for serial port device drivers in a generic
way. To do this, we want to have the serial core layer manage the
registered physical serial controller devices.

To manage serial controllers, let's set up a struct bus and struct device
for the serial core controller as suggested by Greg and Jiri. The serial
core controller devices are children of the physical serial port device.
The serial core controller device is needed to support multiple different
kind of ports connected to single physical serial port device.

Let's also set up a struct device for the serial core port. The serial
core port instances are children of the serial core controller device.

With the serial core port device we can now flush pending TX on the
runtime PM resume as suggested by Johan.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Jiri Slaby <jirislaby@kernel.org>
Suggested-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230525113034.46880-1-tony@atomide.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 171 insertions, 21 deletions

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index f856c7fae2fd..29bd5ede0b25 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -17,6 +17,7 @@
 #include <linux/gpio/consumer.h>
 #include <linux/kernel.h>
 #include <linux/of.h>
+#include <linux/pm_runtime.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/device.h>
@@ -31,6 +32,8 @@
 #include <linux/irq.h>
 #include <linux/uaccess.h>
 
+#include "serial_base.h"
+
 /*
  * This is used to lock changes in serial line configuration.
  */
@@ -134,9 +137,30 @@ static void __uart_start(struct tty_struct *tty)
 {
 	struct uart_state *state = tty->driver_data;
 	struct uart_port *port = state->uart_port;
+	struct serial_port_device *port_dev;
+	int err;
+
+	if (!port || port->flags & UPF_DEAD || uart_tx_stopped(port))
+		return;
+
+	port_dev = port->port_dev;
+
+	/* Increment the runtime PM usage count for the active check below */
+	err = pm_runtime_get(&port_dev->dev);
+	if (err < 0) {
+		pm_runtime_put_noidle(&port_dev->dev);
+		return;
+	}
 
-	if (port && !(port->flags & UPF_DEAD) && !uart_tx_stopped(port))
+	/*
+	 * Start TX if enabled, and kick runtime PM. If the device is not
+	 * enabled, serial_port_runtime_resume() calls start_tx() again
+	 * after enabling the device.
+	 */
+	if (pm_runtime_active(&port_dev->dev))
 		port->ops->start_tx(port);
+	pm_runtime_mark_last_busy(&port_dev->dev);
+	pm_runtime_put_autosuspend(&port_dev->dev);
 }
 
 static void uart_start(struct tty_struct *tty)
@@ -3048,7 +3072,7 @@ 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.
  *
@@ -3057,8 +3081,9 @@ static const struct attribute_group tty_dev_attr_group = {
  * This allows the driver @drv to register its own uart_port structure with the
  * 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.
+ * Caller must hold port_mutex.
  */
-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;
@@ -3072,7 +3097,6 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 	state = drv->state + uport->line;
 	port = &state->port;
 
-	mutex_lock(&port_mutex);
 	mutex_lock(&port->mutex);
 	if (state->uart_port) {
 		ret = -EINVAL;
@@ -3137,21 +3161,14 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 		       uport->line);
 	}
 
-	/*
-	 * Ensure UPF_DEAD is not set.
-	 */
-	uport->flags &= ~UPF_DEAD;
-
  out:
 	mutex_unlock(&port->mutex);
-	mutex_unlock(&port_mutex);
 
 	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
  *
@@ -3159,20 +3176,16 @@ 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.
+ * Caller must hold port_mutex.
  */
-void uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
+static void 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;
 	struct uart_port *uart_port;
 	struct tty_struct *tty;
 
-	mutex_lock(&port_mutex);
-
-	/*
-	 * Mark the port "dead" - this prevents any opens from
-	 * succeeding while we shut down the port.
-	 */
 	mutex_lock(&port->mutex);
 	uart_port = uart_port_check(state);
 	if (uart_port != uport)
@@ -3183,7 +3196,6 @@ void uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
 		mutex_unlock(&port->mutex);
 		goto out;
 	}
-	uport->flags |= UPF_DEAD;
 	mutex_unlock(&port->mutex);
 
 	/*
@@ -3215,6 +3227,7 @@ void 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;
 
 	mutex_lock(&port->mutex);
 	WARN_ON(atomic_dec_return(&state->refcount) < 0);
@@ -3224,7 +3237,6 @@ void uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
 out:
 	mutex_unlock(&port_mutex);
 }
-EXPORT_SYMBOL(uart_remove_one_port);
 
 /**
  * uart_match_port - are the two ports equivalent?
@@ -3259,6 +3271,144 @@ bool uart_match_port(const struct uart_port *port1,
 }
 EXPORT_SYMBOL(uart_match_port);
 
+static struct serial_ctrl_device *
+serial_core_get_ctrl_dev(struct serial_port_device *port_dev)
+{
+	struct device *dev = &port_dev->dev;
+
+	return to_serial_base_ctrl_device(dev->parent);
+}
+
+/*
+ * 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 serial_ctrl_device *serial_core_ctrl_find(struct uart_driver *drv,
+							struct device *phys_dev,
+							int ctrl_id)
+{
+	struct uart_state *state;
+	int i;
+
+	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 serial_core_get_ctrl_dev(state->uart_port->port_dev);
+	}
+
+	return NULL;
+}
+
+static struct serial_ctrl_device *serial_core_ctrl_device_add(struct uart_port *port)
+{
+	return serial_base_ctrl_add(port, port->dev);
+}
+
+static int serial_core_port_device_add(struct serial_ctrl_device *ctrl_dev,
+				       struct uart_port *port)
+{
+	struct serial_port_device *port_dev;
+
+	port_dev = serial_base_port_add(port, ctrl_dev);
+	if (IS_ERR(port_dev))
+		return PTR_ERR(port_dev);
+
+	port->port_dev = port_dev;
+
+	return 0;
+}
+
+/*
+ * 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 serial_ctrl_device *ctrl_dev, *new_ctrl_dev = NULL;
+	int ret;
+
+	mutex_lock(&port_mutex);
+
+	/*
+	 * Prevent serial_port_runtime_resume() from trying to use the port
+	 * until serial_core_add_one_port() has completed
+	 */
+	port->flags |= UPF_DEAD;
+
+	/* Inititalize a serial core controller device if needed */
+	ctrl_dev = serial_core_ctrl_find(drv, port->dev, port->ctrl_id);
+	if (!ctrl_dev) {
+		new_ctrl_dev = serial_core_ctrl_device_add(port);
+		if (!new_ctrl_dev) {
+			ret = -ENODEV;
+			goto err_unlock;
+		}
+		ctrl_dev = new_ctrl_dev;
+	}
+
+	/*
+	 * Initialize a serial core port device. Tag the port dead to prevent
+	 * serial_port_runtime_resume() trying to do anything until port has
+	 * been registered. It gets cleared by serial_core_add_one_port().
+	 */
+	ret = serial_core_port_device_add(ctrl_dev, port);
+	if (ret)
+		goto err_unregister_ctrl_dev;
+
+	ret = serial_core_add_one_port(drv, port);
+	if (ret)
+		goto err_unregister_port_dev;
+
+	port->flags &= ~UPF_DEAD;
+
+	mutex_unlock(&port_mutex);
+
+	return 0;
+
+err_unregister_port_dev:
+	serial_base_port_device_remove(port->port_dev);
+
+err_unregister_ctrl_dev:
+	serial_base_ctrl_device_remove(new_ctrl_dev);
+
+err_unlock:
+	mutex_unlock(&port_mutex);
+
+	return ret;
+}
+
+/*
+ * 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 serial_port_device *port_dev = port->port_dev;
+	struct serial_ctrl_device *ctrl_dev = serial_core_get_ctrl_dev(port_dev);
+	int ctrl_id = port->ctrl_id;
+
+	mutex_lock(&port_mutex);
+
+	port->flags |= UPF_DEAD;
+
+	serial_core_remove_one_port(drv, port);
+
+	/* Note that struct uart_port *port is no longer valid at this point */
+	serial_base_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_ctrl_device_remove(ctrl_dev);
+
+	mutex_unlock(&port_mutex);
+}
+
 /**
  * uart_handle_dcd_change - handle a change of carrier detect state
  * @uport: uart_port structure for the open port