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Diffstat (limited to 'Documentation/input/input-programming.rst')
| -rw-r--r-- | Documentation/input/input-programming.rst | 68 |
1 files changed, 57 insertions, 11 deletions
diff --git a/Documentation/input/input-programming.rst b/Documentation/input/input-programming.rst index 45a4c6e05e39..c9264814c7aa 100644 --- a/Documentation/input/input-programming.rst +++ b/Documentation/input/input-programming.rst @@ -85,15 +85,15 @@ accepted by this input device. Our example device can only generate EV_KEY type events, and from those only BTN_0 event code. Thus we only set these two bits. We could have used:: - set_bit(EV_KEY, button_dev.evbit); - set_bit(BTN_0, button_dev.keybit); + set_bit(EV_KEY, button_dev->evbit); + set_bit(BTN_0, button_dev->keybit); as well, but with more than single bits the first approach tends to be shorter. Then the example driver registers the input device structure by calling:: - input_register_device(&button_dev); + input_register_device(button_dev); This adds the button_dev structure to linked lists of the input driver and calls device handler modules _connect functions to tell them a new input @@ -120,7 +120,7 @@ Then there is the:: call to tell those who receive the events that we've sent a complete report. This doesn't seem important in the one button case, but is quite important -for for example mouse movement, where you don't want the X and Y values +for example for mouse movement, where you don't want the X and Y values to be interpreted separately, because that'd result in a different movement. dev->open() and dev->close() @@ -128,7 +128,7 @@ dev->open() and dev->close() In case the driver has to repeatedly poll the device, because it doesn't have an interrupt coming from it and the polling is too expensive to be done -all the time, or if the device uses a valuable resource (eg. interrupt), it +all the time, or if the device uses a valuable resource (e.g. interrupt), it can use the open and close callback to know when it can stop polling or release the interrupt and when it must resume polling or grab the interrupt again. To do that, we would add this to our example driver:: @@ -161,9 +161,55 @@ makes sure that dev->open() is called only when the first user connects to the device and that dev->close() is called when the very last user disconnects. Calls to both callbacks are serialized. -The open() callback should return a 0 in case of success or any nonzero value +The open() callback should return a 0 in case of success or any non-zero value in case of failure. The close() callback (which is void) must always succeed. +Inhibiting input devices +~~~~~~~~~~~~~~~~~~~~~~~~ + +Inhibiting a device means ignoring input events from it. As such it is about +maintaining relationships with input handlers - either already existing +relationships, or relationships to be established while the device is in +inhibited state. + +If a device is inhibited, no input handler will receive events from it. + +The fact that nobody wants events from the device is exploited further, by +calling device's close() (if there are users) and open() (if there are users) on +inhibit and uninhibit operations, respectively. Indeed, the meaning of close() +is to stop providing events to the input core and that of open() is to start +providing events to the input core. + +Calling the device's close() method on inhibit (if there are users) allows the +driver to save power. Either by directly powering down the device or by +releasing the runtime-PM reference it got in open() when the driver is using +runtime-PM. + +Inhibiting and uninhibiting are orthogonal to opening and closing the device by +input handlers. Userspace might want to inhibit a device in anticipation before +any handler is positively matched against it. + +Inhibiting and uninhibiting are orthogonal to device's being a wakeup source, +too. Being a wakeup source plays a role when the system is sleeping, not when +the system is operating. How drivers should program their interaction between +inhibiting, sleeping and being a wakeup source is driver-specific. + +Taking the analogy with the network devices - bringing a network interface down +doesn't mean that it should be impossible be wake the system up on LAN through +this interface. So, there may be input drivers which should be considered wakeup +sources even when inhibited. Actually, in many I2C input devices their interrupt +is declared a wakeup interrupt and its handling happens in driver's core, which +is not aware of input-specific inhibit (nor should it be). Composite devices +containing several interfaces can be inhibited on a per-interface basis and e.g. +inhibiting one interface shouldn't affect the device's capability of being a +wakeup source. + +If a device is to be considered a wakeup source while inhibited, special care +must be taken when programming its suspend(), as it might need to call device's +open(). Depending on what close() means for the device in question, not +opening() it before going to sleep might make it impossible to provide any +wakeup events. The device is going to sleep anyway. + Basic event types ~~~~~~~~~~~~~~~~~ @@ -173,8 +219,8 @@ It's reported to the input system via:: input_report_key(struct input_dev *dev, int code, int value) See uapi/linux/input-event-codes.h for the allowable values of code (from 0 to -KEY_MAX). Value is interpreted as a truth value, ie any nonzero value means key -pressed, zero value means key released. The input code generates events only +KEY_MAX). Value is interpreted as a truth value, i.e. any non-zero value means +key pressed, zero value means key released. The input code generates events only in case the value is different from before. In addition to EV_KEY, there are two more basic event types: EV_REL and @@ -185,12 +231,12 @@ because it doesn't have any absolute coordinate system to work in. Absolute events are namely for joysticks and digitizers - devices that do work in an absolute coordinate systems. -Having the device report EV_REL buttons is as simple as with EV_KEY, simply +Having the device report EV_REL buttons is as simple as with EV_KEY; simply set the corresponding bits and call the:: input_report_rel(struct input_dev *dev, int code, int value) -function. Events are generated only for nonzero value. +function. Events are generated only for non-zero values. However EV_ABS requires a little special care. Before calling input_register_device, you have to fill additional fields in the input_dev @@ -234,7 +280,7 @@ device driver. It's a string like 'Generic button device' containing a user friendly name of the device. The id* fields contain the bus ID (PCI, USB, ...), vendor ID and device ID -of the device. The bus IDs are defined in input.h. The vendor and device ids +of the device. The bus IDs are defined in input.h. The vendor and device IDs are defined in pci_ids.h, usb_ids.h and similar include files. These fields should be set by the input device driver before registering it. |