1 .. SPDX-License-Identifier: GPL-2.0
2
3 =======================================
4 Linux wireless regulatory documentation
5 =======================================
6
7 This document gives a brief review over how the Linux wireless
8 regulatory infrastructure works.
9
10 More up to date information can be obtained at the project's web page:
11
12 https://wireless.wiki.kernel.org/en/developers/Regulatory
13
14 Keeping regulatory domains in userspace
15 ---------------------------------------
16
17 Due to the dynamic nature of regulatory domains we keep them
18 in userspace and provide a framework for userspace to upload
19 to the kernel one regulatory domain to be used as the central
20 core regulatory domain all wireless devices should adhere to.
21
22 How to get regulatory domains to the kernel
23 -------------------------------------------
24
25 When the regulatory domain is first set up, the kernel will request a
26 database file (regulatory.db) containing all the regulatory rules. It
27 will then use that database when it needs to look up the rules for a
28 given country.
29
30 How to get regulatory domains to the kernel (old CRDA solution)
31 ---------------------------------------------------------------
32
33 Userspace gets a regulatory domain in the kernel by having
34 a userspace agent build it and send it via nl80211. Only
35 expected regulatory domains will be respected by the kernel.
36
37 A currently available userspace agent which can accomplish this
38 is CRDA - central regulatory domain agent. Its documented here:
39
40 https://wireless.wiki.kernel.org/en/developers/Regulatory/CRDA
41
42 Essentially the kernel will send a udev event when it knows
43 it needs a new regulatory domain. A udev rule can be put in place
44 to trigger crda to send the respective regulatory domain for a
45 specific ISO/IEC 3166 alpha2.
46
47 Below is an example udev rule which can be used:
48
49 # Example file, should be put in /etc/udev/rules.d/regulatory.rules
50 KERNEL=="regulatory*", ACTION=="change", SUBSYSTEM=="platform", RUN+="/sbin/crda"
51
52 The alpha2 is passed as an environment variable under the variable COUNTRY.
53
54 Who asks for regulatory domains?
55 --------------------------------
56
57 * Users
58
59 Users can use iw:
60
61 https://wireless.wiki.kernel.org/en/users/Documentation/iw
62
63 An example::
64
65 # set regulatory domain to "Costa Rica"
66 iw reg set CR
67
68 This will request the kernel to set the regulatory domain to
69 the specified alpha2. The kernel in turn will then ask userspace
70 to provide a regulatory domain for the alpha2 specified by the user
71 by sending a uevent.
72
73 * Wireless subsystems for Country Information elements
74
75 The kernel will send a uevent to inform userspace a new
76 regulatory domain is required. More on this to be added
77 as its integration is added.
78
79 * Drivers
80
81 If drivers determine they need a specific regulatory domain
82 set they can inform the wireless core using regulatory_hint().
83 They have two options -- they either provide an alpha2 so that
84 crda can provide back a regulatory domain for that country or
85 they can build their own regulatory domain based on internal
86 custom knowledge so the wireless core can respect it.
87
88 *Most* drivers will rely on the first mechanism of providing a
89 regulatory hint with an alpha2. For these drivers there is an additional
90 check that can be used to ensure compliance based on custom EEPROM
91 regulatory data. This additional check can be used by drivers by
92 registering on its struct wiphy a reg_notifier() callback. This notifier
93 is called when the core's regulatory domain has been changed. The driver
94 can use this to review the changes made and also review who made them
95 (driver, user, country IE) and determine what to allow based on its
96 internal EEPROM data. Devices drivers wishing to be capable of world
97 roaming should use this callback. More on world roaming will be
98 added to this document when its support is enabled.
99
100 Device drivers who provide their own built regulatory domain
101 do not need a callback as the channels registered by them are
102 the only ones that will be allowed and therefore *additional*
103 channels cannot be enabled.
104
105 Example code - drivers hinting an alpha2:
106 ------------------------------------------
107
108 This example comes from the zd1211rw device driver. You can start
109 by having a mapping of your device's EEPROM country/regulatory
110 domain value to a specific alpha2 as follows::
111
112 static struct zd_reg_alpha2_map reg_alpha2_map[] = {
113 { ZD_REGDOMAIN_FCC, "US" },
114 { ZD_REGDOMAIN_IC, "CA" },
115 { ZD_REGDOMAIN_ETSI, "DE" }, /* Generic ETSI, use most restrictive */
116 { ZD_REGDOMAIN_JAPAN, "JP" },
117 { ZD_REGDOMAIN_JAPAN_ADD, "JP" },
118 { ZD_REGDOMAIN_SPAIN, "ES" },
119 { ZD_REGDOMAIN_FRANCE, "FR" },
120
121 Then you can define a routine to map your read EEPROM value to an alpha2,
122 as follows::
123
124 static int zd_reg2alpha2(u8 regdomain, char *alpha2)
125 {
126 unsigned int i;
127 struct zd_reg_alpha2_map *reg_map;
128 for (i = 0; i < ARRAY_SIZE(reg_alpha2_map); i++) {
129 reg_map = ®_alpha2_map[i];
130 if (regdomain == reg_map->reg) {
131 alpha2[0] = reg_map->alpha2[0];
132 alpha2[1] = reg_map->alpha2[1];
133 return 0;
134 }
135 }
136 return 1;
137 }
138
139 Lastly, you can then hint to the core of your discovered alpha2, if a match
140 was found. You need to do this after you have registered your wiphy. You
141 are expected to do this during initialization.
142
143 ::
144
145 r = zd_reg2alpha2(mac->regdomain, alpha2);
146 if (!r)
147 regulatory_hint(hw->wiphy, alpha2);
148
149 Example code - drivers providing a built in regulatory domain:
150 --------------------------------------------------------------
151
152 [NOTE: This API is not currently available, it can be added when required]
153
154 If you have regulatory information you can obtain from your
155 driver and you *need* to use this we let you build a regulatory domain
156 structure and pass it to the wireless core. To do this you should
157 kmalloc() a structure big enough to hold your regulatory domain
158 structure and you should then fill it with your data. Finally you simply
159 call regulatory_hint() with the regulatory domain structure in it.
160
161 Below is a simple example, with a regulatory domain cached using the stack.
162 Your implementation may vary (read EEPROM cache instead, for example).
163
164 Example cache of some regulatory domain::
165
166 struct ieee80211_regdomain mydriver_jp_regdom = {
167 .n_reg_rules = 3,
168 .alpha2 = "JP",
169 //.alpha2 = "99", /* If I have no alpha2 to map it to */
170 .reg_rules = {
171 /* IEEE 802.11b/g, channels 1..14 */
172 REG_RULE(2412-10, 2484+10, 40, 6, 20, 0),
173 /* IEEE 802.11a, channels 34..48 */
174 REG_RULE(5170-10, 5240+10, 40, 6, 20,
175 NL80211_RRF_NO_IR),
176 /* IEEE 802.11a, channels 52..64 */
177 REG_RULE(5260-10, 5320+10, 40, 6, 20,
178 NL80211_RRF_NO_IR|
179 NL80211_RRF_DFS),
180 }
181 };
182
183 Then in some part of your code after your wiphy has been registered::
184
185 struct ieee80211_regdomain *rd;
186 int size_of_regd;
187 int num_rules = mydriver_jp_regdom.n_reg_rules;
188 unsigned int i;
189
190 size_of_regd = sizeof(struct ieee80211_regdomain) +
191 (num_rules * sizeof(struct ieee80211_reg_rule));
192
193 rd = kzalloc(size_of_regd, GFP_KERNEL);
194 if (!rd)
195 return -ENOMEM;
196
197 memcpy(rd, &mydriver_jp_regdom, sizeof(struct ieee80211_regdomain));
198
199 for (i=0; i < num_rules; i++)
200 memcpy(&rd->reg_rules[i],
201 &mydriver_jp_regdom.reg_rules[i],
202 sizeof(struct ieee80211_reg_rule));
203 regulatory_struct_hint(rd);
204
205 Statically compiled regulatory database
206 ---------------------------------------
207
208 When a database should be fixed into the kernel, it can be provided as a
209 firmware file at build time that is then linked into the kernel.
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