1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * dev-path-parser.c - EFI Device Path parser
4  * Copyright (C) 2016 Lukas Wunner <lukas@wunner.de>
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License (version 2) as
8  * published by the Free Software Foundation.
9  */
10 
11 #include <linux/acpi.h>
12 #include <linux/efi.h>
13 #include <linux/pci.h>
14 
15 static long __init parse_acpi_path(const struct efi_dev_path *node,
16 				   struct device *parent, struct device **child)
17 {
18 	char hid[ACPI_ID_LEN], uid[11]; /* UINT_MAX + null byte */
19 	struct acpi_device *adev;
20 	struct device *phys_dev;
21 
22 	if (node->header.length != 12)
23 		return -EINVAL;
24 
25 	sprintf(hid, "%c%c%c%04X",
26 		'A' + ((node->acpi.hid >> 10) & 0x1f) - 1,
27 		'A' + ((node->acpi.hid >>  5) & 0x1f) - 1,
28 		'A' + ((node->acpi.hid >>  0) & 0x1f) - 1,
29 			node->acpi.hid >> 16);
30 	sprintf(uid, "%u", node->acpi.uid);
31 
32 	for_each_acpi_dev_match(adev, hid, NULL, -1) {
33 		if (adev->pnp.unique_id && !strcmp(adev->pnp.unique_id, uid))
34 			break;
35 		if (!adev->pnp.unique_id && node->acpi.uid == 0)
36 			break;
37 	}
38 	if (!adev)
39 		return -ENODEV;
40 
41 	phys_dev = acpi_get_first_physical_node(adev);
42 	if (phys_dev) {
43 		*child = get_device(phys_dev);
44 		acpi_dev_put(adev);
45 	} else
46 		*child = &adev->dev;
47 
48 	return 0;
49 }
50 
51 static int __init match_pci_dev(struct device *dev, void *data)
52 {
53 	unsigned int devfn = *(unsigned int *)data;
54 
55 	return dev_is_pci(dev) && to_pci_dev(dev)->devfn == devfn;
56 }
57 
58 static long __init parse_pci_path(const struct efi_dev_path *node,
59 				  struct device *parent, struct device **child)
60 {
61 	unsigned int devfn;
62 
63 	if (node->header.length != 6)
64 		return -EINVAL;
65 	if (!parent)
66 		return -EINVAL;
67 
68 	devfn = PCI_DEVFN(node->pci.dev, node->pci.fn);
69 
70 	*child = device_find_child(parent, &devfn, match_pci_dev);
71 	if (!*child)
72 		return -ENODEV;
73 
74 	return 0;
75 }
76 
77 /*
78  * Insert parsers for further node types here.
79  *
80  * Each parser takes a pointer to the @node and to the @parent (will be NULL
81  * for the first device path node). If a device corresponding to @node was
82  * found below @parent, its reference count should be incremented and the
83  * device returned in @child.
84  *
85  * The return value should be 0 on success or a negative int on failure.
86  * The special return values 0x01 (EFI_DEV_END_INSTANCE) and 0xFF
87  * (EFI_DEV_END_ENTIRE) signal the end of the device path, only
88  * parse_end_path() is supposed to return this.
89  *
90  * Be sure to validate the node length and contents before commencing the
91  * search for a device.
92  */
93 
94 static long __init parse_end_path(const struct efi_dev_path *node,
95 				  struct device *parent, struct device **child)
96 {
97 	if (node->header.length != 4)
98 		return -EINVAL;
99 	if (node->header.sub_type != EFI_DEV_END_INSTANCE &&
100 	    node->header.sub_type != EFI_DEV_END_ENTIRE)
101 		return -EINVAL;
102 	if (!parent)
103 		return -ENODEV;
104 
105 	*child = get_device(parent);
106 	return node->header.sub_type;
107 }
108 
109 /**
110  * efi_get_device_by_path - find device by EFI Device Path
111  * @node: EFI Device Path
112  * @len: maximum length of EFI Device Path in bytes
113  *
114  * Parse a series of EFI Device Path nodes at @node and find the corresponding
115  * device.  If the device was found, its reference count is incremented and a
116  * pointer to it is returned.  The caller needs to drop the reference with
117  * put_device() after use.  The @node pointer is updated to point to the
118  * location immediately after the "End of Hardware Device Path" node.
119  *
120  * If another Device Path instance follows, @len is decremented by the number
121  * of bytes consumed.  Otherwise @len is set to %0.
122  *
123  * If a Device Path node is malformed or its corresponding device is not found,
124  * @node is updated to point to this offending node and an ERR_PTR is returned.
125  *
126  * If @len is initially %0, the function returns %NULL.  Thus, to iterate over
127  * all instances in a path, the following idiom may be used:
128  *
129  *	while (!IS_ERR_OR_NULL(dev = efi_get_device_by_path(&node, &len))) {
130  *		// do something with dev
131  *		put_device(dev);
132  *	}
133  *	if (IS_ERR(dev))
134  *		// report error
135  *
136  * Devices can only be found if they're already instantiated. Most buses
137  * instantiate devices in the "subsys" initcall level, hence the earliest
138  * initcall level in which this function should be called is "fs".
139  *
140  * Returns the device on success or
141  *	%ERR_PTR(-ENODEV) if no device was found,
142  *	%ERR_PTR(-EINVAL) if a node is malformed or exceeds @len,
143  *	%ERR_PTR(-ENOTSUPP) if support for a node type is not yet implemented.
144  */
145 struct device * __init efi_get_device_by_path(const struct efi_dev_path **node,
146 					      size_t *len)
147 {
148 	struct device *parent = NULL, *child;
149 	long ret = 0;
150 
151 	if (!*len)
152 		return NULL;
153 
154 	while (!ret) {
155 		if (*len < 4 || *len < (*node)->header.length)
156 			ret = -EINVAL;
157 		else if ((*node)->header.type		== EFI_DEV_ACPI &&
158 			 (*node)->header.sub_type	== EFI_DEV_BASIC_ACPI)
159 			ret = parse_acpi_path(*node, parent, &child);
160 		else if ((*node)->header.type		== EFI_DEV_HW &&
161 			 (*node)->header.sub_type	== EFI_DEV_PCI)
162 			ret = parse_pci_path(*node, parent, &child);
163 		else if (((*node)->header.type		== EFI_DEV_END_PATH ||
164 			  (*node)->header.type		== EFI_DEV_END_PATH2))
165 			ret = parse_end_path(*node, parent, &child);
166 		else
167 			ret = -ENOTSUPP;
168 
169 		put_device(parent);
170 		if (ret < 0)
171 			return ERR_PTR(ret);
172 
173 		parent = child;
174 		*node  = (void *)*node + (*node)->header.length;
175 		*len  -= (*node)->header.length;
176 	}
177 
178 	if (ret == EFI_DEV_END_ENTIRE)
179 		*len = 0;
180 
181 	return child;
182 }
183