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Luis R. Rodriguezb2e1b302008-09-09 23:19:48 -07001Linux wireless regulatory documentation
2---------------------------------------
3
4This document gives a brief review over how the Linux wireless
5regulatory infrastructure works.
6
7More up to date information can be obtained at the project's web page:
8
9http://wireless.kernel.org/en/developers/Regulatory
10
11Keeping regulatory domains in userspace
12---------------------------------------
13
14Due to the dynamic nature of regulatory domains we keep them
15in userspace and provide a framework for userspace to upload
16to the kernel one regulatory domain to be used as the central
17core regulatory domain all wireless devices should adhere to.
18
19How to get regulatory domains to the kernel
20-------------------------------------------
21
22Userspace gets a regulatory domain in the kernel by having
23a userspace agent build it and send it via nl80211. Only
24expected regulatory domains will be respected by the kernel.
25
26A currently available userspace agent which can accomplish this
27is CRDA - central regulatory domain agent. Its documented here:
28
29http://wireless.kernel.org/en/developers/Regulatory/CRDA
30
31Essentially the kernel will send a udev event when it knows
32it needs a new regulatory domain. A udev rule can be put in place
33to trigger crda to send the respective regulatory domain for a
34specific ISO/IEC 3166 alpha2.
35
36Below is an example udev rule which can be used:
37
38# Example file, should be put in /etc/udev/rules.d/regulatory.rules
39KERNEL=="regulatory*", ACTION=="change", SUBSYSTEM=="platform", RUN+="/sbin/crda"
40
41The alpha2 is passed as an environment variable under the variable COUNTRY.
42
43Who asks for regulatory domains?
44--------------------------------
45
46* Users
47
48Users can use iw:
49
50http://wireless.kernel.org/en/users/Documentation/iw
51
52An example:
53
54 # set regulatory domain to "Costa Rica"
55 iw reg set CR
56
57This will request the kernel to set the regulatory domain to
58the specificied alpha2. The kernel in turn will then ask userspace
59to provide a regulatory domain for the alpha2 specified by the user
60by sending a uevent.
61
62* Wireless subsystems for Country Information elements
63
64The kernel will send a uevent to inform userspace a new
65regulatory domain is required. More on this to be added
66as its integration is added.
67
68* Drivers
69
70If drivers determine they need a specific regulatory domain
71set they can inform the wireless core using regulatory_hint().
72They have two options -- they either provide an alpha2 so that
73crda can provide back a regulatory domain for that country or
74they can build their own regulatory domain based on internal
75custom knowledge so the wireless core can respect it.
76
77*Most* drivers will rely on the first mechanism of providing a
78regulatory hint with an alpha2. For these drivers there is an additional
79check that can be used to ensure compliance based on custom EEPROM
80regulatory data. This additional check can be used by drivers by
81registering on its struct wiphy a reg_notifier() callback. This notifier
82is called when the core's regulatory domain has been changed. The driver
83can use this to review the changes made and also review who made them
84(driver, user, country IE) and determine what to allow based on its
85internal EEPROM data. Devices drivers wishing to be capable of world
86roaming should use this callback. More on world roaming will be
87added to this document when its support is enabled.
88
89Device drivers who provide their own built regulatory domain
90do not need a callback as the channels registered by them are
91the only ones that will be allowed and therefore *additional*
92cannels cannot be enabled.
93
94Example code - drivers hinting an alpha2:
95------------------------------------------
96
97This example comes from the zd1211rw device driver. You can start
98by having a mapping of your device's EEPROM country/regulatory
99domain value to to a specific alpha2 as follows:
100
101static struct zd_reg_alpha2_map reg_alpha2_map[] = {
102 { ZD_REGDOMAIN_FCC, "US" },
103 { ZD_REGDOMAIN_IC, "CA" },
104 { ZD_REGDOMAIN_ETSI, "DE" }, /* Generic ETSI, use most restrictive */
105 { ZD_REGDOMAIN_JAPAN, "JP" },
106 { ZD_REGDOMAIN_JAPAN_ADD, "JP" },
107 { ZD_REGDOMAIN_SPAIN, "ES" },
108 { ZD_REGDOMAIN_FRANCE, "FR" },
109
110Then you can define a routine to map your read EEPROM value to an alpha2,
111as follows:
112
113static int zd_reg2alpha2(u8 regdomain, char *alpha2)
114{
115 unsigned int i;
116 struct zd_reg_alpha2_map *reg_map;
117 for (i = 0; i < ARRAY_SIZE(reg_alpha2_map); i++) {
118 reg_map = &reg_alpha2_map[i];
119 if (regdomain == reg_map->reg) {
120 alpha2[0] = reg_map->alpha2[0];
121 alpha2[1] = reg_map->alpha2[1];
122 return 0;
123 }
124 }
125 return 1;
126}
127
128Lastly, you can then hint to the core of your discovered alpha2, if a match
129was found. You need to do this after you have registered your wiphy. You
130are expected to do this during initialization.
131
132 r = zd_reg2alpha2(mac->regdomain, alpha2);
133 if (!r)
134 regulatory_hint(hw->wiphy, alpha2, NULL);
135
136Example code - drivers providing a built in regulatory domain:
137--------------------------------------------------------------
138
139If you have regulatory information you can obtain from your
140driver and you *need* to use this we let you build a regulatory domain
141structure and pass it to the wireless core. To do this you should
142kmalloc() a structure big enough to hold your regulatory domain
143structure and you should then fill it with your data. Finally you simply
144call regulatory_hint() with the regulatory domain structure in it.
145
146Bellow is a simple example, with a regulatory domain cached using the stack.
147Your implementation may vary (read EEPROM cache instead, for example).
148
149Example cache of some regulatory domain
150
151struct ieee80211_regdomain mydriver_jp_regdom = {
152 .n_reg_rules = 3,
153 .alpha2 = "JP",
154 //.alpha2 = "99", /* If I have no alpha2 to map it to */
155 .reg_rules = {
156 /* IEEE 802.11b/g, channels 1..14 */
157 REG_RULE(2412-20, 2484+20, 40, 6, 20, 0),
158 /* IEEE 802.11a, channels 34..48 */
159 REG_RULE(5170-20, 5240+20, 40, 6, 20,
160 NL80211_RRF_PASSIVE_SCAN),
161 /* IEEE 802.11a, channels 52..64 */
162 REG_RULE(5260-20, 5320+20, 40, 6, 20,
163 NL80211_RRF_NO_IBSS |
164 NL80211_RRF_DFS),
165 }
166};
167
168Then in some part of your code after your wiphy has been registered:
169
170 int r;
171 struct ieee80211_regdomain *rd;
172 int size_of_regd;
173 int num_rules = mydriver_jp_regdom.n_reg_rules;
174 unsigned int i;
175
176 size_of_regd = sizeof(struct ieee80211_regdomain) +
177 (num_rules * sizeof(struct ieee80211_reg_rule));
178
179 rd = kzalloc(size_of_regd, GFP_KERNEL);
180 if (!rd)
181 return -ENOMEM;
182
183 memcpy(rd, &mydriver_jp_regdom, sizeof(struct ieee80211_regdomain));
184
185 for (i=0; i < num_rules; i++) {
186 memcpy(&rd->reg_rules[i], &mydriver_jp_regdom.reg_rules[i],
187 sizeof(struct ieee80211_reg_rule));
188 }
189 r = regulatory_hint(hw->wiphy, NULL, rd);
190 if (r) {
191 kfree(rd);
192 return r;
193 }
194