[PATCH] evdev: Add support for TRACKPOINT_CONST_ACCEL udev property

[Hans de Goede]

There is quite a wide spread in the delta events generated by trackpoints,
some generate deltas of 1-2 under normal use, while others generate deltas
from 1-20.

It is desirable to normalize trackpoint deltas just like we are normalizing
mouse deltas to 1000 dpi, so as to give different model laptops aprox.
the same trackpoint cursor speed ootb.

Recent versions of udev + hwdb set a TRACKPOINT_CONST_ACCEL udev property
which can be used to adjust trackpoints which are too slow / too fast
ootb, this commit implements support for that property.

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 src/evdev.c         | 33 +++++++++++++++++++++++++++++++++
 src/evdev.h         |  7 +++++++
 src/libinput-util.c | 31 +++++++++++++++++++++++++++++++
 src/libinput-util.h |  1 +
 4 files changed, 72 insertions(+)

diff --git a/src/evdev.c b/src/evdev.c
index 2808c30..3c63d67 100644
--- a/src/evdev.c
+++ b/src/evdev.c
@@ -1319,6 +1319,31 @@ evdev_read_wheel_click_prop(struct evdev_device *device)
 
 	return angle;
 }
+
+static inline int
+evdev_get_trackpoint_dpi(struct evdev_device *device)
+{
+	struct libinput *libinput = device->base.seat->libinput;
+	const char *trackpoint_accel;
+	double accel = DEFAULT_TRACKPOINT_ACCEL;
+
+	trackpoint_accel = udev_device_get_property_value(
+				device->udev_device, "TRACKPOINT_CONST_ACCEL");
+	if (trackpoint_accel) {
+		accel = parse_trackpoint_accel_property(trackpoint_accel);
+		if (accel == 0.0) {
+			log_error(libinput, "Trackpoint accel property for "
+					    "'%s' is present but invalid, "
+					    "using %.2f instead\n",
+					    device->devname,
+					    DEFAULT_TRACKPOINT_ACCEL);
+			accel = DEFAULT_TRACKPOINT_ACCEL;
+		}
+	}
+
+	return DEFAULT_MOUSE_DPI * accel;
+}
+
 static inline int
 evdev_read_dpi_prop(struct evdev_device *device)
 {
@@ -1326,6 +1351,14 @@ evdev_read_dpi_prop(struct evdev_device *device)
 	const char *mouse_dpi;
 	int dpi = DEFAULT_MOUSE_DPI;
 
+	/*
+	 * Trackpoints do not have dpi, instead hwdb may contain a
+	 * TRACKPOINT_CONST_ACCEL value to compensate for sensitity differences
+	 * between different models, we translate this to a fake dpi.
+	 */
+	if (libevdev_has_property(device->evdev, INPUT_PROP_POINTING_STICK))
+		return evdev_get_trackpoint_dpi(device);
+
 	mouse_dpi = udev_device_get_property_value(device->udev_device,
 						   "MOUSE_DPI");
 	if (mouse_dpi) {
diff --git a/src/evdev.h b/src/evdev.h
index c7a9e75..b63ae86 100644
--- a/src/evdev.h
+++ b/src/evdev.h
@@ -36,6 +36,13 @@
 
 /* The HW DPI rate we normalize to before calculating pointer acceleration */
 #define DEFAULT_MOUSE_DPI 1000
+
+/*
+ * The constant (linear) acceleration factor we use to normalize trackpoint
+ * deltas before calculating pointer acceleration.
+ */
+#define DEFAULT_TRACKPOINT_ACCEL 1.0
+
 /* The fake resolution value for abs devices without resolution */
 #define EVDEV_FAKE_RESOLUTION 1
 
diff --git a/src/libinput-util.c b/src/libinput-util.c
index 49e297a..5891012 100644
--- a/src/libinput-util.c
+++ b/src/libinput-util.c
@@ -29,6 +29,7 @@
 #include "config.h"
 
 #include <ctype.h>
+#include <locale.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -201,3 +202,33 @@ parse_mouse_wheel_click_angle_property(const char *prop)
 
         return angle;
 }
+
+/**
+ * Helper function to parse the TRACKPOINT_CONST_ACCEL property from udev.
+ * Property is of the form:
+ * TRACKPOINT_CONST_ACCEL=<float>
+ *
+ * @param prop The value of the udev property (without the TRACKPOINT_CONST_ACCEL=)
+ * @return The acceleration, or 0.0 on error.
+ */
+double
+parse_trackpoint_accel_property(const char *prop)
+{
+	locale_t c_locale;
+	double accel;
+	char *endp;
+
+	/* Create a "C" locale to force strtod to use '.' as seperator */
+	c_locale = newlocale(LC_NUMERIC_MASK, "C", (locale_t)0);
+	if (c_locale == (locale_t)0)
+		return 0.0;
+
+	accel = strtod_l(prop, &endp, c_locale);
+
+	freelocale(c_locale);
+
+	if (*endp != '\0')
+		return 0.0;
+
+	return accel;
+}
diff --git a/src/libinput-util.h b/src/libinput-util.h
index 30f59ec..74226b9 100644
--- a/src/libinput-util.h
+++ b/src/libinput-util.h
@@ -242,5 +242,6 @@ enum ratelimit_state ratelimit_test(struct ratelimit *r);
 
 int parse_mouse_dpi_property(const char *prop);
 int parse_mouse_wheel_click_angle_property(const char *prop);
+double parse_trackpoint_accel_property(const char *prop);
 
 #endif /* LIBINPUT_UTIL_H */
-- 
2.3.4