xref: /openbmc/linux/drivers/tty/serial/serial_port.c (revision f0931824)
1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * Serial core port device driver
4  *
5  * Copyright (C) 2023 Texas Instruments Incorporated - https://www.ti.com/
6  * Author: Tony Lindgren <tony@atomide.com>
7  */
8 
9 #include <linux/device.h>
10 #include <linux/module.h>
11 #include <linux/pm_runtime.h>
12 #include <linux/serial_core.h>
13 #include <linux/spinlock.h>
14 
15 #include "serial_base.h"
16 
17 #define SERIAL_PORT_AUTOSUSPEND_DELAY_MS	500
18 
19 /* Only considers pending TX for now. Caller must take care of locking */
20 static int __serial_port_busy(struct uart_port *port)
21 {
22 	return !uart_tx_stopped(port) &&
23 		uart_circ_chars_pending(&port->state->xmit);
24 }
25 
26 static int serial_port_runtime_resume(struct device *dev)
27 {
28 	struct serial_port_device *port_dev = to_serial_base_port_device(dev);
29 	struct uart_port *port;
30 	unsigned long flags;
31 
32 	port = port_dev->port;
33 
34 	if (port->flags & UPF_DEAD)
35 		goto out;
36 
37 	/* Flush any pending TX for the port */
38 	spin_lock_irqsave(&port->lock, flags);
39 	if (!port_dev->tx_enabled)
40 		goto unlock;
41 	if (__serial_port_busy(port))
42 		port->ops->start_tx(port);
43 
44 unlock:
45 	spin_unlock_irqrestore(&port->lock, flags);
46 
47 out:
48 	pm_runtime_mark_last_busy(dev);
49 
50 	return 0;
51 }
52 
53 static int serial_port_runtime_suspend(struct device *dev)
54 {
55 	struct serial_port_device *port_dev = to_serial_base_port_device(dev);
56 	struct uart_port *port = port_dev->port;
57 	unsigned long flags;
58 	bool busy;
59 
60 	if (port->flags & UPF_DEAD)
61 		return 0;
62 
63 	uart_port_lock_irqsave(port, &flags);
64 	if (!port_dev->tx_enabled) {
65 		uart_port_unlock_irqrestore(port, flags);
66 		return 0;
67 	}
68 
69 	busy = __serial_port_busy(port);
70 	if (busy)
71 		port->ops->start_tx(port);
72 	uart_port_unlock_irqrestore(port, flags);
73 
74 	if (busy)
75 		pm_runtime_mark_last_busy(dev);
76 
77 	return busy ? -EBUSY : 0;
78 }
79 
80 static void serial_base_port_set_tx(struct uart_port *port,
81 				    struct serial_port_device *port_dev,
82 				    bool enabled)
83 {
84 	unsigned long flags;
85 
86 	uart_port_lock_irqsave(port, &flags);
87 	port_dev->tx_enabled = enabled;
88 	uart_port_unlock_irqrestore(port, flags);
89 }
90 
91 void serial_base_port_startup(struct uart_port *port)
92 {
93 	struct serial_port_device *port_dev = port->port_dev;
94 
95 	serial_base_port_set_tx(port, port_dev, true);
96 }
97 
98 void serial_base_port_shutdown(struct uart_port *port)
99 {
100 	struct serial_port_device *port_dev = port->port_dev;
101 
102 	serial_base_port_set_tx(port, port_dev, false);
103 }
104 
105 static DEFINE_RUNTIME_DEV_PM_OPS(serial_port_pm,
106 				 serial_port_runtime_suspend,
107 				 serial_port_runtime_resume, NULL);
108 
109 static int serial_port_probe(struct device *dev)
110 {
111 	pm_runtime_enable(dev);
112 	pm_runtime_set_autosuspend_delay(dev, SERIAL_PORT_AUTOSUSPEND_DELAY_MS);
113 	pm_runtime_use_autosuspend(dev);
114 
115 	return 0;
116 }
117 
118 static int serial_port_remove(struct device *dev)
119 {
120 	pm_runtime_dont_use_autosuspend(dev);
121 	pm_runtime_disable(dev);
122 
123 	return 0;
124 }
125 
126 /*
127  * Serial core port device init functions. Note that the physical serial
128  * port device driver may not have completed probe at this point.
129  */
130 int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
131 {
132 	return serial_ctrl_register_port(drv, port);
133 }
134 EXPORT_SYMBOL(uart_add_one_port);
135 
136 void uart_remove_one_port(struct uart_driver *drv, struct uart_port *port)
137 {
138 	serial_ctrl_unregister_port(drv, port);
139 }
140 EXPORT_SYMBOL(uart_remove_one_port);
141 
142 static struct device_driver serial_port_driver = {
143 	.name = "port",
144 	.suppress_bind_attrs = true,
145 	.probe = serial_port_probe,
146 	.remove = serial_port_remove,
147 	.pm = pm_ptr(&serial_port_pm),
148 };
149 
150 int serial_base_port_init(void)
151 {
152 	return serial_base_driver_register(&serial_port_driver);
153 }
154 
155 void serial_base_port_exit(void)
156 {
157 	serial_base_driver_unregister(&serial_port_driver);
158 }
159 
160 MODULE_AUTHOR("Tony Lindgren <tony@atomide.com>");
161 MODULE_DESCRIPTION("Serial controller port driver");
162 MODULE_LICENSE("GPL");
163