Input: convert input-programming doc into ReST format
This file require minimum adjustments to be a valid ReST file. Do it, in order to be able to parse it with Sphinx. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
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~~~~~~~~~~~~~~~~~~~~~~~~~
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Programming input drivers
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~~~~~~~~~~~~~~~~~~~~~~~~~
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1. Creating an input device driver
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Creating an input device driver
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===============================
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1.0 The simplest example
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~~~~~~~~~~~~~~~~~~~~~~~~
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The simplest example
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~~~~~~~~~~~~~~~~~~~~
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Here comes a very simple example of an input device driver. The device has
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just one button and the button is accessible at i/o port BUTTON_PORT. When
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pressed or released a BUTTON_IRQ happens. The driver could look like:
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pressed or released a BUTTON_IRQ happens. The driver could look like::
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#include <linux/input.h>
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#include <linux/module.h>
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@ -70,8 +71,8 @@ static void __exit button_exit(void)
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module_init(button_init);
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module_exit(button_exit);
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1.1 What the example does
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~~~~~~~~~~~~~~~~~~~~~~~~~
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What the example does
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~~~~~~~~~~~~~~~~~~~~~
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First it has to include the <linux/input.h> file, which interfaces to the
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input subsystem. This provides all the definitions needed.
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@ -85,7 +86,7 @@ and sets up input bitfields. This way the device driver tells the other
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parts of the input systems what it is - what events can be generated or
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accepted by this input device. Our example device can only generate EV_KEY
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type events, and from those only BTN_0 event code. Thus we only set these
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two bits. We could have used
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two bits. We could have used::
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set_bit(EV_KEY, button_dev.evbit);
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set_bit(BTN_0, button_dev.keybit);
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@ -93,7 +94,7 @@ two bits. We could have used
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as well, but with more than single bits the first approach tends to be
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shorter.
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Then the example driver registers the input device structure by calling
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Then the example driver registers the input device structure by calling::
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input_register_device(&button_dev);
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@ -102,12 +103,12 @@ calls device handler modules _connect functions to tell them a new input
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device has appeared. input_register_device() may sleep and therefore must
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not be called from an interrupt or with a spinlock held.
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While in use, the only used function of the driver is
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While in use, the only used function of the driver is::
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button_interrupt()
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which upon every interrupt from the button checks its state and reports it
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via the
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via the::
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input_report_key()
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@ -116,7 +117,7 @@ routine isn't reporting two same value events (press, press for example) to
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the input system, because the input_report_* functions check that
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themselves.
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Then there is the
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Then there is the::
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input_sync()
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@ -125,15 +126,15 @@ This doesn't seem important in the one button case, but is quite important
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for for example mouse movement, where you don't want the X and Y values
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to be interpreted separately, because that'd result in a different movement.
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1.2 dev->open() and dev->close()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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dev->open() and dev->close()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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In case the driver has to repeatedly poll the device, because it doesn't
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have an interrupt coming from it and the polling is too expensive to be done
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all the time, or if the device uses a valuable resource (eg. interrupt), it
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can use the open and close callback to know when it can stop polling or
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release the interrupt and when it must resume polling or grab the interrupt
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again. To do that, we would add this to our example driver:
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again. To do that, we would add this to our example driver::
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static int button_open(struct input_dev *dev)
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{
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@ -166,11 +167,11 @@ disconnects. Calls to both callbacks are serialized.
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The open() callback should return a 0 in case of success or any nonzero value
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in case of failure. The close() callback (which is void) must always succeed.
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1.3 Basic event types
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~~~~~~~~~~~~~~~~~~~~~
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Basic event types
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~~~~~~~~~~~~~~~~~
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The most simple event type is EV_KEY, which is used for keys and buttons.
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It's reported to the input system via:
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It's reported to the input system via::
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input_report_key(struct input_dev *dev, int code, int value)
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@ -188,7 +189,7 @@ events are namely for joysticks and digitizers - devices that do work in an
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absolute coordinate systems.
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Having the device report EV_REL buttons is as simple as with EV_KEY, simply
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set the corresponding bits and call the
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set the corresponding bits and call the::
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input_report_rel(struct input_dev *dev, int code, int value)
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@ -197,14 +198,14 @@ function. Events are generated only for nonzero value.
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However EV_ABS requires a little special care. Before calling
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input_register_device, you have to fill additional fields in the input_dev
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struct for each absolute axis your device has. If our button device had also
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the ABS_X axis:
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the ABS_X axis::
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button_dev.absmin[ABS_X] = 0;
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button_dev.absmax[ABS_X] = 255;
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button_dev.absfuzz[ABS_X] = 4;
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button_dev.absflat[ABS_X] = 8;
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Or, you can just say:
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Or, you can just say::
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input_set_abs_params(button_dev, ABS_X, 0, 255, 4, 8);
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@ -218,18 +219,18 @@ If you don't need absfuzz and absflat, you can set them to zero, which mean
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that the thing is precise and always returns to exactly the center position
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(if it has any).
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1.4 BITS_TO_LONGS(), BIT_WORD(), BIT_MASK()
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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BITS_TO_LONGS(), BIT_WORD(), BIT_MASK()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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These three macros from bitops.h help some bitfield computations:
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These three macros from bitops.h help some bitfield computations::
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BITS_TO_LONGS(x) - returns the length of a bitfield array in longs for
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x bits
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BIT_WORD(x) - returns the index in the array in longs for bit x
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BIT_MASK(x) - returns the index in a long for bit x
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1.5 The id* and name fields
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The id* and name fields
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~~~~~~~~~~~~~~~~~~~~~~~
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The dev->name should be set before registering the input device by the input
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device driver. It's a string like 'Generic button device' containing a
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The id and name fields can be passed to userland via the evdev interface.
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1.6 The keycode, keycodemax, keycodesize fields
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The keycode, keycodemax, keycodesize fields
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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These three fields should be used by input devices that have dense keymaps.
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The keycode is an array used to map from scancodes to input system keycodes.
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rely on kernel's default implementation of setting and querying keycode
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mappings.
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1.7 dev->getkeycode() and dev->setkeycode()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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dev->getkeycode() and dev->setkeycode()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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getkeycode() and setkeycode() callbacks allow drivers to override default
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keycode/keycodesize/keycodemax mapping mechanism provided by input core
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and implement sparse keycode maps.
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1.8 Key autorepeat
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~~~~~~~~~~~~~~~~~~
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Key autorepeat
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~~~~~~~~~~~~~~
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... is simple. It is handled by the input.c module. Hardware autorepeat is
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not used, because it's not present in many devices and even where it is
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autorepeat for your device, just set EV_REP in dev->evbit. All will be
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handled by the input system.
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1.9 Other event types, handling output events
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Other event types, handling output events
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The other event types up to now are:
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EV_LED - used for the keyboard LEDs.
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EV_SND - used for keyboard beeps.
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- EV_LED - used for the keyboard LEDs.
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- EV_SND - used for keyboard beeps.
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They are very similar to for example key events, but they go in the other
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direction - from the system to the input device driver. If your input device
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driver can handle these events, it has to set the respective bits in evbit,
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*and* also the callback routine:
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*and* also the callback routine::
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button_dev->event = button_event;
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int button_event(struct input_dev *dev, unsigned int type, unsigned int code, int value);
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int button_event(struct input_dev *dev, unsigned int type,
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unsigned int code, int value)
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{
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if (type == EV_SND && code == SND_BELL) {
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outb(value, BUTTON_BELL);
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