[systemd-devel] [PATCH] udev: input_id: tag accelerometers as ID_INPUT_ACCELEROMETER

[Benjamin Tissoires]

On Apr 03 2015 or thereabouts, Hans de Goede wrote:
> Hi,
> 
> On 03-04-15 15:51, David Herrmann wrote:
> >Hi
> >
> >On Fri, Apr 3, 2015 at 12:07 PM, Hans de Goede <hdegoede at redhat.com> wrote:
> >>input_id already (tries to) tag accelerometers as such, but this only works
> >>for absolute accelerometers. Recent kernels mark accelerometers through an
> >>input prop. Trust that prop and always tag devices with it with
> >>ID_INPUT_ACCELEROMETER.
> >>
> >>Note that detection by the prop bit works the same as the existing detection
> >>and will ensure that no other tags get set on the device.
> >>
> >>Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> >>---
> >>  src/shared/missing.h             | 4 ++++
> >>  src/udev/udev-builtin-input_id.c | 5 +++++
> >>  2 files changed, 9 insertions(+)
> >>
> >>diff --git a/src/shared/missing.h b/src/shared/missing.h
> >>index 3bdfd8f..4464e35 100644
> >>--- a/src/shared/missing.h
> >>+++ b/src/shared/missing.h
> >>@@ -944,3 +944,7 @@ static inline int kcmp(pid_t pid1, pid_t pid2, int type, unsigned long idx1, uns
> >>  #ifndef INPUT_PROP_POINTING_STICK
> >>  #define INPUT_PROP_POINTING_STICK 0x05
> >>  #endif
> >>+
> >>+#ifndef INPUT_PROP_ACCELEROMETER
> >>+#define INPUT_PROP_ACCELEROMETER  0x06
> >>+#endif
> >>diff --git a/src/udev/udev-builtin-input_id.c b/src/udev/udev-builtin-input_id.c
> >>index d4c38ca..ecfc447 100644
> >>--- a/src/udev/udev-builtin-input_id.c
> >>+++ b/src/udev/udev-builtin-input_id.c
> >>@@ -136,6 +136,11 @@ static void test_pointers (struct udev_device *dev,
> >>          int is_mouse = 0;
> >>          int is_touchpad = 0;
> >>
> >>+        if (test_bit (INPUT_PROP_ACCELEROMETER, bitmask_props)) {
> >>+                udev_builtin_add_property(dev, test, "ID_INPUT_ACCELEROMETER", "1");
> >>+                return;
> >>+        }
> >>+
> >
> >So this property is only set for accelerometer-only devices?
> 
> Hmm, good question. Currently I see only one user of it in the kernel:
> 
> drivers/hid/wacom_wac.c

Yep, this is the first and only for now.

> 
> Which most likely does not count as an accelerometer only device, so maybe
> my idea to follow the existing accelerometer detection code and short-circuit
> the other tests was not such a good idea.
> 
> Benjamin, do you have any input on this ?

See Peter's documentation patch here:
https://patchwork.kernel.org/patch/6102851/

If the property is set, "Directional axes on this device (absolute
and/or relative x, y, z) represent accelerometer data. All other axes
retain their meaning. A device must not mix regular directional axes and
accelerometer axes on the same event node."

So we can have multiple axis, multiple buttons but X,Y,Z will be accel
values.

The Cintiq 27 QHD has a builtin accelerometer and it is reported by this
property to explicitly say that the X,Y,Z are not stylus data but
accelerometers values.

For this device, there is no problem because libwacom will set
ID_INPUT_TABLET through a custom udev rule, but for others, the "return"
will be a problem IMO (note that Wacom already breaks the ID_INPUT_* tag
should be set only once per device).

Hope this helps.

Cheers,
Benjamin