解决linux系统WIFI无法使用5GHz频率的问题

李迟按：

这篇文章讲述的是在ubuntu14.04系统上使用WIFI功能5GHz频率的问题，问题本身不大，但基于笔者经验和认知，还是走了些弯路，这里记录一下解决过程，写点东西，留点回忆。

遇到问题

对于WIFI热点的创建，除了从未知到入门这一大坎外，其它的路途还是很顺利的。上峰要求的WIFI是5GHz，但作为技术要求，我必须要考虑2.4GHz和5GHz。首先在一台Ubuntu14.04系统上测试5GHz频率热点，一切正常。但换到另一台裁剪过的Ubuntu14.04上就有问题(正常的ubuntu体积比较大，而这台裁剪过的系统只有500MB)。

问题是，使用iw list查看，所有的5GHz的信道都不能使用，信息如下：

root@latelee:~# iw list
Wiphy phy0
        Band 2:
                Capabilities: 0x19e3
                        RX LDPC
                        HT20/HT40
                        Static SM Power Save
                        RX HT20 SGI
                        RX HT40 SGI
                        TX STBC
                        RX STBC 1-stream
                        Max AMSDU length: 7935 bytes
                        DSSS/CCK HT40
                Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
                Minimum RX AMPDU time spacing: 8 usec (0x06)
                HT TX/RX MCS rate indexes supported: 0-15
                Frequencies:
                        * 5180 MHz [36] (30.0 dBm) (passive scanning, no IBSS)
                        * 5200 MHz [40] (30.0 dBm) (passive scanning, no IBSS)
                        * 5220 MHz [44] (30.0 dBm) (passive scanning, no IBSS)
                        * 5240 MHz [48] (30.0 dBm) (passive scanning, no IBSS)
                        * 5260 MHz [52] (30.0 dBm) (passive scanning, no IBSS, radar detection)
                        * 5280 MHz [56] (30.0 dBm) (passive scanning, no IBSS, radar detection)
                        * 5300 MHz [60] (30.0 dBm) (passive scanning, no IBSS, radar detection)
                        * 5320 MHz [64] (30.0 dBm) (passive scanning, no IBSS, radar detection)
                        * 5500 MHz [100] (disabled)
                        * 5520 MHz [104] (disabled)
                        * 5540 MHz [108] (disabled)
                        * 5560 MHz [112] (disabled)
                        * 5580 MHz [116] (disabled)
                        * 5600 MHz [120] (disabled)
                        * 5620 MHz [124] (disabled)
                        * 5640 MHz [128] (disabled)
                        * 5660 MHz [132] (disabled)
                        * 5680 MHz [136] (disabled)
                        * 5700 MHz [140] (disabled)
                        * 5745 MHz [149] (30.0 dBm) (passive scanning, no IBSS)
                        * 5765 MHz [153] (30.0 dBm) (passive scanning, no IBSS)
                        * 5785 MHz [157] (30.0 dBm) (passive scanning, no IBSS)
                        * 5805 MHz [161] (30.0 dBm) (passive scanning, no IBSS)
                        * 5825 MHz [165] (30.0 dBm) (passive scanning, no IBSS)

从网上查到的信息，当信道后面有disabled或passive scanning字样时，这个信道是无法正常使用(于AP模式)的。从启动信息也可以看到有些信道是被禁止的，如下：

[   10.921565] ath10k: qca988x hw2.0 (0x4100016c, 0x043222ff) fw 10.1.467.1-1 api 2 htt 2.1
[   10.921572] ath10k: debug 0 debugfs 0 tracing 0 dfs 0
[   11.414145] ath: EEPROM regdomain: 0x0
[   11.414151] ath: EEPROM indicates default country code should be used
[   11.414154] ath: doing EEPROM country->regdmn map search
[   11.414157] ath: country maps to regdmn code: 0x3a
[   11.414159] ath: Country alpha2 being used: US
[   11.414162] ath: Regpair used: 0x3a
[   11.414225] cfg80211: Updating information on frequency 2412 MHz with regulatory rule:
[   11.414229] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414233] cfg80211: Updating information on frequency 2417 MHz with regulatory rule:
[   11.414236] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414240] cfg80211: Updating information on frequency 2422 MHz with regulatory rule:
[   11.414243] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414246] cfg80211: Updating information on frequency 2427 MHz with regulatory rule:
[   11.414249] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414252] cfg80211: Updating information on frequency 2432 MHz with regulatory rule:
[   11.414256] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414259] cfg80211: Updating information on frequency 2437 MHz with regulatory rule:
[   11.414262] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414265] cfg80211: Updating information on frequency 2442 MHz with regulatory rule:
[   11.414269] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414272] cfg80211: Updating information on frequency 2447 MHz with regulatory rule:
[   11.414275] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414278] cfg80211: Updating information on frequency 2452 MHz with regulatory rule:
[   11.414282] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414285] cfg80211: Updating information on frequency 2457 MHz with regulatory rule:
[   11.414288] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414291] cfg80211: Updating information on frequency 2462 MHz with regulatory rule:
[   11.414294] cfg80211: 2402000 KHz - 2472000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414298] cfg80211: Updating information on frequency 2467 MHz with regulatory rule:
[   11.414301] cfg80211: 2457000 KHz - 2482000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414304] cfg80211: Updating information on frequency 2472 MHz with regulatory rule:
[   11.414307] cfg80211: 2457000 KHz - 2482000 KHz @ 40000 KHz), (600 mBi, 2000 mBm)
[   11.414311] cfg80211: Updating information on frequency 2484 MHz with regulatory rule:
[   11.414314] cfg80211: 2474000 KHz - 2494000 KHz @ 20000 KHz), (600 mBi, 2000 mBm)
[   11.414317] cfg80211: Updating information on frequency 5180 MHz with regulatory rule:
[   11.414321] cfg80211: 5170000 KHz - 5250000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414324] cfg80211: Updating information on frequency 5200 MHz with regulatory rule:
[   11.414327] cfg80211: 5170000 KHz - 5250000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414331] cfg80211: Updating information on frequency 5220 MHz with regulatory rule:
[   11.414334] cfg80211: 5170000 KHz - 5250000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414337] cfg80211: Updating information on frequency 5240 MHz with regulatory rule:
[   11.414340] cfg80211: 5170000 KHz - 5250000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414344] cfg80211: Updating information on frequency 5260 MHz with regulatory rule:
[   11.414347] cfg80211: 5250000 KHz - 5330000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414350] cfg80211: Updating information on frequency 5280 MHz with regulatory rule:
[   11.414354] cfg80211: 5250000 KHz - 5330000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414357] cfg80211: Updating information on frequency 5300 MHz with regulatory rule:
[   11.414360] cfg80211: 5250000 KHz - 5330000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414363] cfg80211: Updating information on frequency 5320 MHz with regulatory rule:
[   11.414367] cfg80211: 5250000 KHz - 5330000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414370] cfg80211: Updating information on frequency 5500 MHz with regulatory rule:
[   11.414373] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414376] cfg80211: Updating information on frequency 5520 MHz with regulatory rule:
[   11.414380] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414383] cfg80211: Updating information on frequency 5540 MHz with regulatory rule:
[   11.414386] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414389] cfg80211: Updating information on frequency 5560 MHz with regulatory rule:
[   11.414393] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414396] cfg80211: Updating information on frequency 5580 MHz with regulatory rule:
[   11.414399] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414403] cfg80211: Updating information on frequency 5600 MHz with regulatory rule:
[   11.414406] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414409] cfg80211: Updating information on frequency 5620 MHz with regulatory rule:
[   11.414412] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414416] cfg80211: Updating information on frequency 5640 MHz with regulatory rule:
[   11.414419] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414422] cfg80211: Updating information on frequency 5660 MHz with regulatory rule:
[   11.414426] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414429] cfg80211: Updating information on frequency 5680 MHz with regulatory rule:
[   11.414432] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414435] cfg80211: Updating information on frequency 5700 MHz with regulatory rule:
[   11.414439] cfg80211: 5490000 KHz - 5730000 KHz @ 160000 KHz), (600 mBi, 2000 mBm)
[   11.414441] cfg80211: Disabling freq 5745 MHz
[   11.414444] cfg80211: Disabling freq 5765 MHz
[   11.414446] cfg80211: Disabling freq 5785 MHz
[   11.414449] cfg80211: Disabling freq 5805 MHz
[   11.414451] cfg80211: Disabling freq 5825 MHz
[   11.415005] cfg80211: Calling CRDA to update world regulatory domain

尝试解决

从网上找到一篇文章，问题和我遇到的很类似，难得的是，作者用的网卡驱动和我的一模一样。于是参考其中的做法，将linux驱动的regd.c文件源码进行修改。然而还是不成功。看到问题不是驱动方面。

接着check一下网卡驱动、固件这些文件是否OK。对应的驱动信息如下：

root@latelee:~# modinfo ath10k_pci
filename:       /lib/modules/3.17.1+/kernel/drivers/net/wireless/ath/ath10k/ath10k_pci.ko
firmware:       ath10k/QCA988X/hw2.0/board.bin
firmware:       ath10k/QCA988X/hw2.0/firmware-2.bin
license:        Dual BSD/GPL
description:    Driver support for Atheros QCA988X PCIe devices
author:         Qualcomm Atheros
depends:        ath10k_core
intree:         Y
vermagic:       3.17.1+ SMP mod_unload modversions 686 
parm:           target_ps:Enable ath10k Target (SoC) PS option (uint)
parm:           irq_mode:0: auto, 1: legacy, 2: msi (default: 0) (uint)
parm:           reset_mode:0: auto, 1: warm only (default: 0) (uint)

驱动找到了，固件也有了，都是已经具备并且都正常的。

解决

继续看linux无线wiki关于CRDA的资料，找到如下关键的段落：

We use userspace events (uevents) to let the kernel speak to userspace. Below is an example udev rule you can place into your distribution's udev rules directory (usually /etc/udev/rules.d/). Note that most distributions have udev configured with inotify on the udev rules directory, so there is no need to restart udev after adding the new rule.


# Example file, should be put in /etc/udev/rules.d/regulatory.rules
KERNEL=="regulatory*", ACTION=="change", SUBSYSTEM=="platform", RUN+="/sbin/crda"

其实我已经看过，之所以没有留意这个，是因为我看过/etc/udev/rules.d/这个目录是不存在的。但我却不知道，它已经变成/lib/udev/rules.d/目录了。于是在原装的Ubuntu系统中找到带“regulatory.rules”字样的文件，放到裁剪过的系统对应目录，问题终于解决了。

总结

为了使用WIFI的5GHz频率，有很多事是要注意的：

1、无线网卡是否支持5GHz。

2、需要CRDA可执行文件：/sbin/crda

3、需要CRDA目录：/lib/crda/

4、udev文件：/lib/udev/rules.d/85-regulatory.rules

最后再提一下，如果要自己移植，最好的方法是使用一台原装的系统进行测试，这样至于有一个正确的环境做对比，以减少弯路。

参考资料：

关于CRDA的Linux官方介绍：https://wireless.wiki.kernel.org/en/developers/Regulatory/CRDA

《HOSTAPD+ATH10K+802.11AC AP的实现方法》：http://www.jackyhe.com/?p=263

李迟  2015.7.24 周日上午