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

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

On Apr 07 2017 or thereabouts, Mauro Carvalho Chehab wrote:
> 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?

Not sure. As I mentioned, I haven' t seen such device myself, but maybe
we should reserve the rest of the 0x0n range for those (0x0a-0x0f). This
would force to bump REL_MAX, but I don't think this is an issue besides
recompiling libevdev and others.

> 
> > I'll try the rest of the series on the MX Master today.
> 
> It would be great if you could test it!

I found some issues, I'll report in the other patches.

Cheers,
Benjamin

> 
> Regards,
> Mauro