xref: /linux/drivers/platform/x86/serdev_helpers.h (revision 79790b6818e96c58fe2bffee1b418c16e64e7b80)
1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3  * In some cases UART attached devices which require an in kernel driver,
4  * e.g. UART attached Bluetooth HCIs are described in the ACPI tables
5  * by an ACPI device with a broken or missing UartSerialBusV2() resource.
6  *
7  * This causes the kernel to create a /dev/ttyS# char-device for the UART
8  * instead of creating an in kernel serdev-controller + serdev-device pair
9  * for the in kernel driver.
10  *
11  * The quirk handling in acpi_quirk_skip_serdev_enumeration() makes the kernel
12  * create a serdev-controller device for these UARTs instead of a /dev/ttyS#.
13  *
14  * Instantiating the actual serdev-device to bind to is up to pdx86 code,
15  * this header provides a helper for getting the serdev-controller device.
16  */
17 #include <linux/acpi.h>
18 #include <linux/device.h>
19 #include <linux/err.h>
20 #include <linux/printk.h>
21 #include <linux/sprintf.h>
22 #include <linux/string.h>
23 
24 static inline struct device *
get_serdev_controller(const char * serial_ctrl_hid,const char * serial_ctrl_uid,int serial_ctrl_port,const char * serdev_ctrl_name)25 get_serdev_controller(const char *serial_ctrl_hid,
26 		      const char *serial_ctrl_uid,
27 		      int serial_ctrl_port,
28 		      const char *serdev_ctrl_name)
29 {
30 	struct device *ctrl_dev, *child;
31 	struct acpi_device *ctrl_adev;
32 	char name[32];
33 	int i;
34 
35 	ctrl_adev = acpi_dev_get_first_match_dev(serial_ctrl_hid, serial_ctrl_uid, -1);
36 	if (!ctrl_adev) {
37 		pr_err("error could not get %s/%s serial-ctrl adev\n",
38 		       serial_ctrl_hid, serial_ctrl_uid);
39 		return ERR_PTR(-ENODEV);
40 	}
41 
42 	/* get_first_physical_node() returns a weak ref */
43 	ctrl_dev = get_device(acpi_get_first_physical_node(ctrl_adev));
44 	if (!ctrl_dev) {
45 		pr_err("error could not get %s/%s serial-ctrl physical node\n",
46 		       serial_ctrl_hid, serial_ctrl_uid);
47 		ctrl_dev = ERR_PTR(-ENODEV);
48 		goto put_ctrl_adev;
49 	}
50 
51 	/* Walk host -> uart-ctrl -> port -> serdev-ctrl */
52 	for (i = 0; i < 3; i++) {
53 		switch (i) {
54 		case 0:
55 			snprintf(name, sizeof(name), "%s:0", dev_name(ctrl_dev));
56 			break;
57 		case 1:
58 			snprintf(name, sizeof(name), "%s.%d",
59 				 dev_name(ctrl_dev), serial_ctrl_port);
60 			break;
61 		case 2:
62 			strscpy(name, serdev_ctrl_name, sizeof(name));
63 			break;
64 		}
65 
66 		child = device_find_child_by_name(ctrl_dev, name);
67 		put_device(ctrl_dev);
68 		if (!child) {
69 			pr_err("error could not find '%s' device\n", name);
70 			ctrl_dev = ERR_PTR(-ENODEV);
71 			goto put_ctrl_adev;
72 		}
73 
74 		ctrl_dev = child;
75 	}
76 
77 put_ctrl_adev:
78 	acpi_dev_put(ctrl_adev);
79 	return ctrl_dev;
80 }
81