Prior to commit 190d7f02ce8e ("HID: input: do not increment usages when
a duplicate is found") from the v4.18 kernel, HID used to shift the
event codes if a duplicate usage was found. This ended up in a situation
where a device would export a ton of ABS_MISC+n event codes, or a ton
of REL_MISC+n event codes.
This is now fixed, however userspace needs to detect those situation.
Fortunately, ABS_MT_SLOT-1 (ABS_MISC+6) was never assigned a code, and
so libinput can detect fake multitouch devices from genuine ones by
checking if ABS_MT_SLOT-1 is set.
Now that we have REL_WHEEL_HI_RES, libinput won't be able to differentiate
true high res mice from some other device in a pre-v4.18 kernel.
Set in stone that the ABS_MISC+6 and REL_MISC+1 are reserved and should not
be used so userspace can properly work around those old kernels.
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
---
Dmitry, I did not take your Acked-by, as I added 2 new events and wanted to
be sure you are still OK.
Jiri, this will still need to go through your tree, as the input-event-codes
changes that introduce REL_WHEEL_HI_RES are in your for-4.20/logitech-highres.
Cheers,
Benjamin
include/uapi/linux/input-event-codes.h | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/include/uapi/linux/input-event-codes.h b/include/uapi/linux/input-event-codes.h
index 29fb891ea337..b5e0e9856c47 100644
--- a/include/uapi/linux/input-event-codes.h
+++ b/include/uapi/linux/input-event-codes.h
@@ -708,7 +708,15 @@
#define REL_DIAL 0x07
#define REL_WHEEL 0x08
#define REL_MISC 0x09
-#define REL_WHEEL_HI_RES 0x0a
+/*
+ * 0x0a is reserved and should not be used in input drivers.
+ * It was used by HID as REL_MISC+1 and userspace needs to detect if
+ * the next REL_* event is correct or is just REL_MISC + n.
+ * We define here REL_RESERVED so userspace can rely on it and detect
+ * the situation described above.
+ */
+#define REL_RESERVED 0x0a
+#define REL_WHEEL_HI_RES 0x0b
#define REL_MAX 0x0f
#define REL_CNT (REL_MAX+1)
@@ -745,6 +753,15 @@
#define ABS_MISC 0x28
+/*
+ * 0x2e is reserved and should not be used in input drivers.
+ * It was used by HID as ABS_MISC+6 and userspace needs to detect if
+ * the next ABS_* event is correct or is just ABS_MISC + n.
+ * We define here ABS_RESERVED so userspace can rely on it and detect
+ * the situation described above.
+ */
+#define ABS_RESERVED 0x2e
+
#define ABS_MT_SLOT 0x2f /* MT slot being modified */
#define ABS_MT_TOUCH_MAJOR 0x30 /* Major axis of touching ellipse */
#define ABS_MT_TOUCH_MINOR 0x31 /* Minor axis (omit if circular) */
--
2.14.3
