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
 15static 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
 51static 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
 58static 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
 94static 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 */
145struct 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}