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Commit ce0879e324df007f12cc25227102847b92fcafb7

Authored by Johannes Berg
Committed by John W. Linville
1 parent 7e9debe978
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

rfkill: improve docs 

Now that the dust has settled a bit, improve the docs on rfkill
and include more information about /dev/rfkill.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

Showing 1 changed file with 69 additions and 68 deletions Side-by-side Diff

Documentation/rfkill.txt
Diff comments   View file @ ce0879e
... ... @@ -3,9 +3,8 @@
3 3  
4 4 1. Introduction
5 5 2. Implementation details
6   -3. Kernel driver guidelines
7   -4. Kernel API
8   -5. Userspace support
  6 +3. Kernel API
  7 +4. Userspace support
9 8  
10 9  
11 10 1. Introduction
12 11  
13 12  
14 13  
15 14  
16 15  
17 16  
18 17  
19 18  
20 19  
21 20  
22 21  
23 22  
24 23  
25 24  
26 25  
... ... @@ -19,83 +18,63 @@
19 18 situations where transmitters need to be turned off, for example on
20 19 aircraft.
21 20  
  21 +The rfkill subsystem has a concept of "hard" and "soft" block, which
  22 +differ little in their meaning (block == transmitters off) but rather in
  23 +whether they can be changed or not:
  24 + - hard block: read-only radio block that cannot be overriden by software
  25 + - soft block: writable radio block (need not be readable) that is set by
  26 + the system software.
22 27  
23 28  
24 29 2. Implementation details
25 30  
26   -The rfkill subsystem is composed of various components: the rfkill class, the
27   -rfkill-input module (an input layer handler), and some specific input layer
28   -events.
  31 +The rfkill subsystem is composed of three main components:
  32 + * the rfkill core,
  33 + * the deprecated rfkill-input module (an input layer handler, being
  34 + replaced by userspace policy code) and
  35 + * the rfkill drivers.
29 36  
30   -The rfkill class is provided for kernel drivers to register their radio
31   -transmitter with the kernel, provide methods for turning it on and off and,
32   -optionally, letting the system know about hardware-disabled states that may
33   -be implemented on the device. This code is enabled with the CONFIG_RFKILL
34   -Kconfig option, which drivers can "select".
  37 +The rfkill core provides API for kernel drivers to register their radio
  38 +transmitter with the kernel, methods for turning it on and off and, letting
  39 +the system know about hardware-disabled states that may be implemented on
  40 +the device.
35 41  
36   -The rfkill class code also notifies userspace of state changes, this is
37   -achieved via uevents. It also provides some sysfs files for userspace to
38   -check the status of radio transmitters. See the "Userspace support" section
39   -below.
  42 +The rfkill core code also notifies userspace of state changes, and provides
  43 +ways for userspace to query the current states. See the "Userspace support"
  44 +section below.
40 45  
41   -
42   -The rfkill-input code implements a basic response to rfkill buttons -- it
43   -implements turning on/off all devices of a certain class (or all).
44   -
45 46 When the device is hard-blocked (either by a call to rfkill_set_hw_state()
46   -or from query_hw_block) set_block() will be invoked but drivers can well
47   -ignore the method call since they can use the return value of the function
48   -rfkill_set_hw_state() to sync the software state instead of keeping track
49   -of calls to set_block().
  47 +or from query_hw_block) set_block() will be invoked for additional software
  48 +block, but drivers can ignore the method call since they can use the return
  49 +value of the function rfkill_set_hw_state() to sync the software state
  50 +instead of keeping track of calls to set_block(). In fact, drivers should
  51 +use the return value of rfkill_set_hw_state() unless the hardware actually
  52 +keeps track of soft and hard block separately.
50 53  
51 54  
52   -The entire functionality is spread over more than one subsystem:
  55 +3. Kernel API
53 56  
54   - * The kernel input layer generates KEY_WWAN, KEY_WLAN etc. and
55   - SW_RFKILL_ALL -- when the user presses a button. Drivers for radio
56   - transmitters generally do not register to the input layer, unless the
57   - device really provides an input device (i.e. a button that has no
58   - effect other than generating a button press event)
59 57  
60   - * The rfkill-input code hooks up to these events and switches the soft-block
61   - of the various radio transmitters, depending on the button type.
  58 +Drivers for radio transmitters normally implement an rfkill driver.
62 59  
63   - * The rfkill drivers turn off/on their transmitters as requested.
64   -
65   - * The rfkill class will generate userspace notifications (uevents) to tell
66   - userspace what the current state is.
67   -
68   -
69   -
70   -3. Kernel driver guidelines
71   -
72   -
73   -Drivers for radio transmitters normally implement only the rfkill class.
74   -These drivers may not unblock the transmitter based on own decisions, they
75   -should act on information provided by the rfkill class only.
76   -
77 60 Platform drivers might implement input devices if the rfkill button is just
78 61 that, a button. If that button influences the hardware then you need to
79   -implement an rfkill class instead. This also applies if the platform provides
  62 +implement an rfkill driver instead. This also applies if the platform provides
80 63 a way to turn on/off the transmitter(s).
81 64  
82   -During suspend/hibernation, transmitters should only be left enabled when
83   -wake-on wlan or similar functionality requires it and the device wasn't
84   -blocked before suspend/hibernate. Note that it may be necessary to update
85   -the rfkill subsystem's idea of what the current state is at resume time if
86   -the state may have changed over suspend.
  65 +For some platforms, it is possible that the hardware state changes during
  66 +suspend/hibernation, in which case it will be necessary to update the rfkill
  67 +core with the current state is at resume time.
87 68  
  69 +To create an rfkill driver, driver's Kconfig needs to have
88 70  
  71 + depends on RFKILL || !RFKILL
89 72  
90   -4. Kernel API
  73 +to ensure the driver cannot be built-in when rfkill is modular. The !RFKILL
  74 +case allows the driver to be built when rfkill is not configured, which which
  75 +case all rfkill API can still be used but will be provided by static inlines
  76 +which compile to almost nothing.
91 77  
92   -To build a driver with rfkill subsystem support, the driver should depend on
93   -(or select) the Kconfig symbol RFKILL.
94   -
95   -The hardware the driver talks to may be write-only (where the current state
96   -of the hardware is unknown), or read-write (where the hardware can be queried
97   -about its current state).
98   -
99 78 Calling rfkill_set_hw_state() when a state change happens is required from
100 79 rfkill drivers that control devices that can be hard-blocked unless they also
101 80 assign the poll_hw_block() callback (then the rfkill core will poll the
102 81  
103 82  
... ... @@ -105,10 +84,33 @@
105 84  
106 85 5. Userspace support
107 86  
108   -The following sysfs entries exist for every rfkill device:
  87 +The recommended userspace interface to use is /dev/rfkill, which is a misc
  88 +character device that allows userspace to obtain and set the state of rfkill
  89 +devices and sets of devices. It also notifies userspace about device addition
  90 +and removal. The API is a simple read/write API that is defined in
  91 +linux/rfkill.h, with one ioctl that allows turning off the deprecated input
  92 +handler in the kernel for the transition period.
109 93  
  94 +Except for the one ioctl, communication with the kernel is done via read()
  95 +and write() of instances of 'struct rfkill_event'. In this structure, the
  96 +soft and hard block are properly separated (unlike sysfs, see below) and
  97 +userspace is able to get a consistent snapshot of all rfkill devices in the
  98 +system. Also, it is possible to switch all rfkill drivers (or all drivers of
  99 +a specified type) into a state which also updates the default state for
  100 +hotplugged devices.
  101 +
  102 +After an application opens /dev/rfkill, it can read the current state of
  103 +all devices, and afterwards can poll the descriptor for hotplug or state
  104 +change events.
  105 +
  106 +Applications must ignore operations (the "op" field) they do not handle,
  107 +this allows the API to be extended in the future.
  108 +
  109 +Additionally, each rfkill device is registered in sysfs and there has the
  110 +following attributes:
  111 +
110 112 name: Name assigned by driver to this key (interface or driver name).
111   - type: Name of the key type ("wlan", "bluetooth", etc).
  113 + type: Driver type string ("wlan", "bluetooth", etc).
112 114 state: Current state of the transmitter
113 115 0: RFKILL_STATE_SOFT_BLOCKED
114 116 transmitter is turned off by software
... ... @@ -117,7 +119,12 @@
117 119 2: RFKILL_STATE_HARD_BLOCKED
118 120 transmitter is forced off by something outside of
119 121 the driver's control.
120   - claim: 0: Kernel handles events (currently always reads that value)
  122 + This file is deprecated because it can only properly show
  123 + three of the four possible states, soft-and-hard-blocked is
  124 + missing.
  125 + claim: 0: Kernel handles events
  126 + This file is deprecated because there no longer is a way to
  127 + claim just control over a single rfkill instance.
121 128  
122 129 rfkill devices also issue uevents (with an action of "change"), with the
123 130 following environment variables set:
... ... @@ -128,10 +135,4 @@
128 135  
129 136 The contents of these variables corresponds to the "name", "state" and
130 137 "type" sysfs files explained above.
131   -
132   -An alternative userspace interface exists as a misc device /dev/rfkill,
133   -which allows userspace to obtain and set the state of rfkill devices and
134   -sets of devices. It also notifies userspace about device addition and
135   -removal. The API is a simple read/write API that is defined in
136   -linux/rfkill.h.