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 
parse_acpi_path(const struct efi_dev_path * node,struct device * parent,struct device ** child)15 static long __init parse_acpi_path(const struct efi_dev_path *node,
16 				   struct device *parent, struct device **child)
17 {
18 	struct acpi_device *adev;
19 	struct device *phys_dev;
20 	char hid[ACPI_ID_LEN];
21 	u64 uid;
22 	int ret;
23 
24 	if (node->header.length != 12)
25 		return -EINVAL;
26 
27 	sprintf(hid, "%c%c%c%04X",
28 		'A' + ((node->acpi.hid >> 10) & 0x1f) - 1,
29 		'A' + ((node->acpi.hid >>  5) & 0x1f) - 1,
30 		'A' + ((node->acpi.hid >>  0) & 0x1f) - 1,
31 			node->acpi.hid >> 16);
32 
33 	for_each_acpi_dev_match(adev, hid, NULL, -1) {
34 		ret = acpi_dev_uid_to_integer(adev, &uid);
35 		if (ret == 0 && node->acpi.uid == uid)
36 			break;
37 		if (ret == -ENODATA && node->acpi.uid == 0)
38 			break;
39 	}
40 	if (!adev)
41 		return -ENODEV;
42 
43 	phys_dev = acpi_get_first_physical_node(adev);
44 	if (phys_dev) {
45 		*child = get_device(phys_dev);
46 		acpi_dev_put(adev);
47 	} else
48 		*child = &adev->dev;
49 
50 	return 0;
51 }
52 
match_pci_dev(struct device * dev,void * data)53 static int __init match_pci_dev(struct device *dev, void *data)
54 {
55 	unsigned int devfn = *(unsigned int *)data;
56 
57 	return dev_is_pci(dev) && to_pci_dev(dev)->devfn == devfn;
58 }
59 
parse_pci_path(const struct efi_dev_path * node,struct device * parent,struct device ** child)60 static long __init parse_pci_path(const struct efi_dev_path *node,
61 				  struct device *parent, struct device **child)
62 {
63 	unsigned int devfn;
64 
65 	if (node->header.length != 6)
66 		return -EINVAL;
67 	if (!parent)
68 		return -EINVAL;
69 
70 	devfn = PCI_DEVFN(node->pci.dev, node->pci.fn);
71 
72 	*child = device_find_child(parent, &devfn, match_pci_dev);
73 	if (!*child)
74 		return -ENODEV;
75 
76 	return 0;
77 }
78 
79 /*
80  * Insert parsers for further node types here.
81  *
82  * Each parser takes a pointer to the @node and to the @parent (will be NULL
83  * for the first device path node). If a device corresponding to @node was
84  * found below @parent, its reference count should be incremented and the
85  * device returned in @child.
86  *
87  * The return value should be 0 on success or a negative int on failure.
88  * The special return values 0x01 (EFI_DEV_END_INSTANCE) and 0xFF
89  * (EFI_DEV_END_ENTIRE) signal the end of the device path, only
90  * parse_end_path() is supposed to return this.
91  *
92  * Be sure to validate the node length and contents before commencing the
93  * search for a device.
94  */
95 
parse_end_path(const struct efi_dev_path * node,struct device * parent,struct device ** child)96 static long __init parse_end_path(const struct efi_dev_path *node,
97 				  struct device *parent, struct device **child)
98 {
99 	if (node->header.length != 4)
100 		return -EINVAL;
101 	if (node->header.sub_type != EFI_DEV_END_INSTANCE &&
102 	    node->header.sub_type != EFI_DEV_END_ENTIRE)
103 		return -EINVAL;
104 	if (!parent)
105 		return -ENODEV;
106 
107 	*child = get_device(parent);
108 	return node->header.sub_type;
109 }
110 
111 /**
112  * efi_get_device_by_path - find device by EFI Device Path
113  * @node: EFI Device Path
114  * @len: maximum length of EFI Device Path in bytes
115  *
116  * Parse a series of EFI Device Path nodes at @node and find the corresponding
117  * device.  If the device was found, its reference count is incremented and a
118  * pointer to it is returned.  The caller needs to drop the reference with
119  * put_device() after use.  The @node pointer is updated to point to the
120  * location immediately after the "End of Hardware Device Path" node.
121  *
122  * If another Device Path instance follows, @len is decremented by the number
123  * of bytes consumed.  Otherwise @len is set to %0.
124  *
125  * If a Device Path node is malformed or its corresponding device is not found,
126  * @node is updated to point to this offending node and an ERR_PTR is returned.
127  *
128  * If @len is initially %0, the function returns %NULL.  Thus, to iterate over
129  * all instances in a path, the following idiom may be used:
130  *
131  *	while (!IS_ERR_OR_NULL(dev = efi_get_device_by_path(&node, &len))) {
132  *		// do something with dev
133  *		put_device(dev);
134  *	}
135  *	if (IS_ERR(dev))
136  *		// report error
137  *
138  * Devices can only be found if they're already instantiated. Most buses
139  * instantiate devices in the "subsys" initcall level, hence the earliest
140  * initcall level in which this function should be called is "fs".
141  *
142  * Returns the device on success or
143  *	%ERR_PTR(-ENODEV) if no device was found,
144  *	%ERR_PTR(-EINVAL) if a node is malformed or exceeds @len,
145  *	%ERR_PTR(-ENOTSUPP) if support for a node type is not yet implemented.
146  */
efi_get_device_by_path(const struct efi_dev_path ** node,size_t * len)147 struct device * __init efi_get_device_by_path(const struct efi_dev_path **node,
148 					      size_t *len)
149 {
150 	struct device *parent = NULL, *child;
151 	long ret = 0;
152 
153 	if (!*len)
154 		return NULL;
155 
156 	while (!ret) {
157 		if (*len < 4 || *len < (*node)->header.length)
158 			ret = -EINVAL;
159 		else if ((*node)->header.type		== EFI_DEV_ACPI &&
160 			 (*node)->header.sub_type	== EFI_DEV_BASIC_ACPI)
161 			ret = parse_acpi_path(*node, parent, &child);
162 		else if ((*node)->header.type		== EFI_DEV_HW &&
163 			 (*node)->header.sub_type	== EFI_DEV_PCI)
164 			ret = parse_pci_path(*node, parent, &child);
165 		else if (((*node)->header.type		== EFI_DEV_END_PATH ||
166 			  (*node)->header.type		== EFI_DEV_END_PATH2))
167 			ret = parse_end_path(*node, parent, &child);
168 		else
169 			ret = -ENOTSUPP;
170 
171 		put_device(parent);
172 		if (ret < 0)
173 			return ERR_PTR(ret);
174 
175 		parent = child;
176 		*node  = (void *)*node + (*node)->header.length;
177 		*len  -= (*node)->header.length;
178 	}
179 
180 	if (ret == EFI_DEV_END_ENTIRE)
181 		*len = 0;
182 
183 	return child;
184 }
185