Re: [PATCH 4/8] HID: input: use the Resolution Multiplier for high-resolution scrolling

[Peter Hutterer <peter.hutterer@who-t.net>]

On Thu, Nov 22, 2018 at 04:34:05PM +1000, Peter Hutterer wrote:
> Windows uses a magic number of 120 for a wheel click. High-resolution
> scroll wheels are supposed to use a fraction of 120 to signal smaller
> scroll steps. This is implemented by the Resolution Multiplier in the
> device itself.

I scooped a dirty old MS Wireless Mobile Mouse 4000 out of a mate's bin and
it breaks this assumption. The resolution multiplier is 16 which isn't an
integer fraction of 120. Real multiplier is 7.5.

The device sends hi-res values of 4, so it should end up as REL_WHEEL_HI_RES
30. We are getting 28 instead which doesn't add up to a nice 120.
Basic assumption: MS uses something other than plain 120 internally.

The choices we have now are:
- use 1200 or 12000 internally and divide by 10 before sending the
  final value
- just make the evdev API use 1200 or 12000 and let userspace deal with it.
  much simpler.

Any suggestions/comments?

Cheers,
   Peter