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 struct acpi_hid_uid {
16 	struct acpi_device_id hid[2];
17 	char uid[11]; /* UINT_MAX + null byte */
18 };
19 
20 static int __init match_acpi_dev(struct device *dev, const void *data)
21 {
22 	struct acpi_hid_uid hid_uid = *(const struct acpi_hid_uid *)data;
23 	struct acpi_device *adev = to_acpi_device(dev);
24 
25 	if (acpi_match_device_ids(adev, hid_uid.hid))
26 		return 0;
27 
28 	if (adev->pnp.unique_id)
29 		return !strcmp(adev->pnp.unique_id, hid_uid.uid);
30 	else
31 		return !strcmp("0", hid_uid.uid);
32 }
33 
34 static long __init parse_acpi_path(struct efi_dev_path *node,
35 				   struct device *parent, struct device **child)
36 {
37 	struct acpi_hid_uid hid_uid = {};
38 	struct device *phys_dev;
39 
40 	if (node->length != 12)
41 		return -EINVAL;
42 
43 	sprintf(hid_uid.hid[0].id, "%c%c%c%04X",
44 		'A' + ((node->acpi.hid >> 10) & 0x1f) - 1,
45 		'A' + ((node->acpi.hid >>  5) & 0x1f) - 1,
46 		'A' + ((node->acpi.hid >>  0) & 0x1f) - 1,
47 			node->acpi.hid >> 16);
48 	sprintf(hid_uid.uid, "%u", node->acpi.uid);
49 
50 	*child = bus_find_device(&acpi_bus_type, NULL, &hid_uid,
51 				 match_acpi_dev);
52 	if (!*child)
53 		return -ENODEV;
54 
55 	phys_dev = acpi_get_first_physical_node(to_acpi_device(*child));
56 	if (phys_dev) {
57 		get_device(phys_dev);
58 		put_device(*child);
59 		*child = phys_dev;
60 	}
61 
62 	return 0;
63 }
64 
65 static int __init match_pci_dev(struct device *dev, void *data)
66 {
67 	unsigned int devfn = *(unsigned int *)data;
68 
69 	return dev_is_pci(dev) && to_pci_dev(dev)->devfn == devfn;
70 }
71 
72 static long __init parse_pci_path(struct efi_dev_path *node,
73 				  struct device *parent, struct device **child)
74 {
75 	unsigned int devfn;
76 
77 	if (node->length != 6)
78 		return -EINVAL;
79 	if (!parent)
80 		return -EINVAL;
81 
82 	devfn = PCI_DEVFN(node->pci.dev, node->pci.fn);
83 
84 	*child = device_find_child(parent, &devfn, match_pci_dev);
85 	if (!*child)
86 		return -ENODEV;
87 
88 	return 0;
89 }
90 
91 /*
92  * Insert parsers for further node types here.
93  *
94  * Each parser takes a pointer to the @node and to the @parent (will be NULL
95  * for the first device path node). If a device corresponding to @node was
96  * found below @parent, its reference count should be incremented and the
97  * device returned in @child.
98  *
99  * The return value should be 0 on success or a negative int on failure.
100  * The special return values 0x01 (EFI_DEV_END_INSTANCE) and 0xFF
101  * (EFI_DEV_END_ENTIRE) signal the end of the device path, only
102  * parse_end_path() is supposed to return this.
103  *
104  * Be sure to validate the node length and contents before commencing the
105  * search for a device.
106  */
107 
108 static long __init parse_end_path(struct efi_dev_path *node,
109 				  struct device *parent, struct device **child)
110 {
111 	if (node->length != 4)
112 		return -EINVAL;
113 	if (node->sub_type != EFI_DEV_END_INSTANCE &&
114 	    node->sub_type != EFI_DEV_END_ENTIRE)
115 		return -EINVAL;
116 	if (!parent)
117 		return -ENODEV;
118 
119 	*child = get_device(parent);
120 	return node->sub_type;
121 }
122 
123 /**
124  * efi_get_device_by_path - find device by EFI Device Path
125  * @node: EFI Device Path
126  * @len: maximum length of EFI Device Path in bytes
127  *
128  * Parse a series of EFI Device Path nodes at @node and find the corresponding
129  * device.  If the device was found, its reference count is incremented and a
130  * pointer to it is returned.  The caller needs to drop the reference with
131  * put_device() after use.  The @node pointer is updated to point to the
132  * location immediately after the "End of Hardware Device Path" node.
133  *
134  * If another Device Path instance follows, @len is decremented by the number
135  * of bytes consumed.  Otherwise @len is set to %0.
136  *
137  * If a Device Path node is malformed or its corresponding device is not found,
138  * @node is updated to point to this offending node and an ERR_PTR is returned.
139  *
140  * If @len is initially %0, the function returns %NULL.  Thus, to iterate over
141  * all instances in a path, the following idiom may be used:
142  *
143  *	while (!IS_ERR_OR_NULL(dev = efi_get_device_by_path(&node, &len))) {
144  *		// do something with dev
145  *		put_device(dev);
146  *	}
147  *	if (IS_ERR(dev))
148  *		// report error
149  *
150  * Devices can only be found if they're already instantiated. Most buses
151  * instantiate devices in the "subsys" initcall level, hence the earliest
152  * initcall level in which this function should be called is "fs".
153  *
154  * Returns the device on success or
155  *	%ERR_PTR(-ENODEV) if no device was found,
156  *	%ERR_PTR(-EINVAL) if a node is malformed or exceeds @len,
157  *	%ERR_PTR(-ENOTSUPP) if support for a node type is not yet implemented.
158  */
159 struct device * __init efi_get_device_by_path(struct efi_dev_path **node,
160 					      size_t *len)
161 {
162 	struct device *parent = NULL, *child;
163 	long ret = 0;
164 
165 	if (!*len)
166 		return NULL;
167 
168 	while (!ret) {
169 		if (*len < 4 || *len < (*node)->length)
170 			ret = -EINVAL;
171 		else if ((*node)->type     == EFI_DEV_ACPI &&
172 			 (*node)->sub_type == EFI_DEV_BASIC_ACPI)
173 			ret = parse_acpi_path(*node, parent, &child);
174 		else if ((*node)->type     == EFI_DEV_HW &&
175 			 (*node)->sub_type == EFI_DEV_PCI)
176 			ret = parse_pci_path(*node, parent, &child);
177 		else if (((*node)->type    == EFI_DEV_END_PATH ||
178 			  (*node)->type    == EFI_DEV_END_PATH2))
179 			ret = parse_end_path(*node, parent, &child);
180 		else
181 			ret = -ENOTSUPP;
182 
183 		put_device(parent);
184 		if (ret < 0)
185 			return ERR_PTR(ret);
186 
187 		parent = child;
188 		*node  = (void *)*node + (*node)->length;
189 		*len  -= (*node)->length;
190 	}
191 
192 	if (ret == EFI_DEV_END_ENTIRE)
193 		*len = 0;
194 
195 	return child;
196 }
197