Re: [v3,1/4] input: add an EV_REL event for high-res vertical wheel

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Fri, 7 Apr 2017 14:17:51 +0200
Benjamin Tissoires <benjamin.tissoires@redhat.com> escreveu:

> Hi Mauro,
> 
> On Apr 07 2017 or thereabouts, Mauro Carvalho Chehab wrote:
> > As some devices can produce either low-res or high-res
> > vertical wheel EV_REL events, add a new event to allow
> > userspace to distinguish between them.
> > 
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> > ---
> >  Documentation/input/event-codes.rst    | 16 +++++++++++++---
> >  include/uapi/linux/input-event-codes.h |  1 +
> >  2 files changed, 14 insertions(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/input/event-codes.rst b/Documentation/input/event-codes.rst
> > index 92db50954169..0c8591d39bc6 100644
> > --- a/Documentation/input/event-codes.rst
> > +++ b/Documentation/input/event-codes.rst
> > @@ -185,10 +185,20 @@ instead of EV_REL codes.
> >  
> >  A few EV_REL codes have special meanings:
> >  
> > -* REL_WHEEL, REL_HWHEEL:
> > +* REL_WHEEL:
> >  
> > -  - These codes are used for vertical and horizontal scroll wheels,
> > -    respectively.
> > +  - These codes are used for vertical scroll wheels.
> > +
> > +  - REL_WHEEL is for normal wheel operational mode, e. g. low-resolution
> > +    (line-based) scroll.
> > +
> > +  - REL_HIRES_WHEEL should be used when the wheel has two resolutions and it
> > +    is in high-resolution mode, e. g. the same angular movement that would
> > +    produce a single REL_WHEEL will produce multiple REL_HIRES_WHEEL events.
> > +
> > +* REL_HWHEEL:
> > +
> > +  - This code is used for horizontal scroll wheels.
> >  
> >  EV_ABS
> >  ------
> > diff --git a/include/uapi/linux/input-event-codes.h b/include/uapi/linux/input-event-codes.h
> > index 3af60ee69053..23b2d377af59 100644
> > --- a/include/uapi/linux/input-event-codes.h
> > +++ b/include/uapi/linux/input-event-codes.h
> > @@ -703,6 +703,7 @@
> >  #define REL_DIAL		0x07
> >  #define REL_WHEEL		0x08
> >  #define REL_MISC		0x09
> > +#define REL_HIRES_WHEEL		0x0a  
> 
> There is one issue here. The HID input layer has a tendency to map
> usages to REL_MISC +1, +2, +3, etc... When it doesn't know how to map an
> usage, the core layer maps it to the next one.
> 
> I am not aware of devices exposing such REL axes, but I wouldn't be
> surprised if the issue will not raise at some point.
> 
> We already had an issue with ABS events where ABS_MISC are conflicting
> with ABS_MT_SLOTS. Luckily, we have a little empty space between
> ABS_MISC and ABS_MT_SLOT, which allows userspace to detect such issues.
> 
> Could you give the define a bigger number (and maybe reserve a couple of
> REL_MISC-n) to make sure that we do not end up with joysticks exporting
> REL_HIRES_WHEEL?

Sure. How many REL_MISC-n should be reserved?

> I'll try the rest of the series on the MX Master today.

It would be great if you could test it!

Regards,
Mauro