On Mon, 29 Oct 2018 at 14:12, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > So what the half-multiplier did, assuming a multiplier of 8 (which is > what my MX Anywhere 2S reports) would be: > > - remainder starts at 3 > - high-res is +1 > - now remainder is 3+1, and it triggers the >= half logic > - 4/8 is 0, but then the code added 1 because high-res was positive, > so the code decides to add 1 > - the code does a wheel update of 1, and updates remainder with -8, > so now it's -4 > > Next time around, if the high-res update is 0 or -1, it will go the > other direction. And then it will oscillate. > > Notice how tiny movements of +1/-1 in the *high-res* count can > translate into +1/-1 in the regular wheel movement. Ah, I see what you mean. So, if we move the threshold to (multiplier - 1)/multiplier (7/8) in this case, I think the equivalent scenario would be: - remainder starts at 7 - high-res is +1 - remainder is now 7+1, triggering a low-res update - 7/8 is 0, but we add one to the remainder in the check making it (7+1)/8 == 1 - we update remainder to -1 This way we're still at least 7/8ths of a notch from the threshold in either direction, so we shouldn't get the oscillation problem. Does that sound reasonable, or do you think I've missed something? > I do not believe that you actually ever *used* that code, or if you > did, you only did so with applications that were high-res aware and > ignored the regular wheel entirely because you were testing in an > environment with other changes than just the kernel. I tested these changes with 5 different Logitech mice (see the Logitech high-res support patch [0] for details), and did so mainly with applications that were *not* high-res aware, using a mix of clicky and smooth modes. Admittedly the MX Anywhere 2S was not one of my test devices; I had assumed that its behaviour would be sufficiently similar to that of the MX Anywhere 2 and the MX Master 2S. Harry Cutts Chrome OS Touch/Input team [0]: https://patchwork.kernel.org/patch/10582935/
