On Fri, Sep 07, 2018 at 10:51:15AM +0200, Benjamin Tissoires wrote:

From: Benjamin Tissoires <redacted>

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_MISC+1 was never assigned a code, and so libinput
can detect fake multitouch devices from genuine ones by checking is
ABS_MISC+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+1 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 <redacted>
---

Hi,

while reviewing my local tree, I realize that we might want to be able
to differentiate older kernels from new ones that export REL_WHEEL_HI_RES.

I know Dmitry was against adding several REL_MISC, so I hope just moving
REL_WHEEL_HI_RES by one and reserving the faulty event codes would be good
this time.

This patch applies on top of the branch for-4.20/logitech-highres from
Jiri's tree. It should go through Jiri's tree as well.

Hm, this is a bit ugly, bit I guess we could spare an event code.

Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

-- 
Dmitry