Hi all,
I would like to share a proposal to extend evdev with support for
pressure sensitive "analog" buttons. It is a feature common on gaming
peripherals (arcade sticks, gamepads, wii guitar) as well now on analog
keyboards such as Wooting One / Two keyboards on which every button is
both analog and digital (so ~100 analog keys).
These devices are difficult to support using the existing evdev API. The
problem is the EV_KEY event type was meant for digital keys, whereas the
EV_ABS could be used for this purpose except that it has reached its
axes limit due to the EVIOCGABS/SABS limitation of 0x40.
The proposal is to add a new event type "EV_PSR" to evdev to describe
pressure sensitive keys. Keys reported to this mechanism can report
analog values. Often devices also report a digital value for the same
button, so EV_PSR analog keys can have a matching digital EV_KEY. For
this reason, we suggest to share key codes. (This is up for debate of
course to tie both together like this.)
Pressure sensitive keys, have similarities with regular absolute axes as
they have min/max values and probably fuzz makes sense as well. It could
be said we should extend ABS like David Herrmann proposed in his ABS2
proposal a while ago and remove the EVIOCGABS/SABS limitations.
This is an initial proposal to address limitations in evdev to improve
device support in existing drivers such as hid-sony, hid-betopff,
psxpad-spi, hid-wii and probably others as well as new devices such as
Wooting keyboards
Thanks,
Roderick Colenbrander
---
Documentation/input/event-codes.rst | 21 +++++++++++++++++++++
include/uapi/linux/input-event-codes.h | 1 +
include/uapi/linux/input.h | 14 ++++++++++++++
3 files changed, 36 insertions(+)
diff --git a/Documentation/input/event-codes.rst
b/Documentation/input/event-codes.rst
index a8c0873beb95..846562d4db4b 100644
--- a/Documentation/input/event-codes.rst
+++ b/Documentation/input/event-codes.rst
@@ -41,6 +41,11 @@ Codes section for details on valid codes for each type.
- Used to describe state changes of keyboards, buttons, or other
key-like
devices.
+* EV_PSR:
+
+ - Used to describe pressure sensitive 'analog' buttons, e.g. analog
buttons
+ on arcade sticks, gamepads or keyboards.
+
* EV_REL:
- Used to describe relative axis value changes, e.g. moving the
mouse 5 units
@@ -177,6 +182,22 @@ a value of 1 in the same synchronization frame.
This usage is deprecated.
Note: In multitouch drivers, the input_mt_report_finger_count()
function should
be used to emit these codes. Please see multi-touch-protocol.txt for
details.
+EV_PSR
+------
+
+EV_PSR events describe absolute changes in a key press-like event. It
is used
+for devices reporting pressure senstive / analog key presses. These events
+can't be described through EV_KEY as it is a digital only interface.
+
+Pressure senstive keys can be found on gaming devices, keyboards and
other devices.
+These devices often report both digital and pressure sensitive events
for a given
+key. For this reason, the KEY_<name> and BTN_<name> codes as defined
for EV_KEY
+are reused. A device supporting digital and pressure sensitive events
for the same
+key, should use the same key code across EV_KEY and EV_PSR.
+
+The value range and resolution for a pressure sensitive button can be
obtained
+through EVIOCGPRS.
+
EV_REL
------
diff --git a/include/uapi/linux/input-event-codes.h
b/include/uapi/linux/input-event-codes.h
index 53fbae27b280..d142498fc64c 100644
--- a/include/uapi/linux/input-event-codes.h
+++ b/include/uapi/linux/input-event-codes.h
@@ -41,6 +41,7 @@
#define EV_ABS 0x03
#define EV_MSC 0x04
#define EV_SW 0x05
+#define EV_PSR 0x06
#define EV_LED 0x11
#define EV_SND 0x12
#define EV_REP 0x14
diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h
index 7288a7c573cc..f5ce2abde800 100644
--- a/include/uapi/linux/input.h
+++ b/include/uapi/linux/input.h
@@ -121,6 +121,17 @@ struct input_mask {
__u64 codes_ptr;
};
+
+/**
+ * struct input_psrinfo - used by EVIOCGPRS/EVIOSPRS ioctls.
+ * @code: pressure sensitive key to query.
+ * @info: value/limits for this key.
+ */
+struct input_psrinfo {
+ __u16 code;
+ struct input_absinfo info; //should this be its own psr specfic struct??
+};
+
#define EVIOCGVERSION _IOR('E', 0x01, int) /* get driver version */
#define EVIOCGID _IOR('E', 0x02, struct input_id) /* get device ID */
#define EVIOCGREP _IOR('E', 0x03, unsigned int[2]) /* get repeat
settings */
@@ -232,6 +243,9 @@ struct input_mask {
*/
#define EVIOCSMASK _IOW('E', 0x93, struct input_mask) /* Set
event-masks */
+#define EVIOCGPSR _IOR('E', 0x94, struct input_psrinfo) /* get psr
value/limits */
+#define EVIOCSPSR _IOW('E', 0x95, struct input_psrinfo) /* set psr
value/limits */
+
#define EVIOCSCLOCKID _IOW('E', 0xa0, int) /* Set clockid to be
used for timestamps */
/*
--
2.14.3
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