On Wed, Feb 11, 2015 at 08:49:16AM +0000, Holmberg, Hans wrote: > > > > As far as I can tell, there is no way to specify values for ABS-"keys" > > > > in the device tree binding. > > > > > > It may not be present in device tree binding, but the driver does > > > support it, so I would rather extend the binding than have a brand new > > driver. > > > > All right, I find it a bit like whacking a round peg down a square hole, but I'll > > head down that path and see where it leads. > > > > This is what I've found: > > A digital joystick driver needs to report three states per axis: min, > max and neutral. The hardware only have two signals per axis(i.e. up > and down) however. See http://wiki.icomp.de/wiki/DB9-Joystick > > This makes gpio-keys pretty much impossible to use for joysticks - as > the driver only reports abs-events when a button/key is pressed, how > would the neutral state be reported? (as there is no signal for > "neutral") > > Even if through some hackery the driver would be modified to report a > special neutral event if all "buttons/keys" for that axis are not > pressed, what value should be reported? An average of the values for > that axis? Also, reporting such an implicit neutral event would > break the behavior of existing abs-reporting instances, right? You have 2 gpio per axis, and since you can't measure how "far" down the axis you have moved the driver should only report values -1, 0, 1 per axis. You start at neutral position, and move right. IRQ for right gpio is fired and you report EV_ABS/ABS_X/1. Then you start moving to the left, gpio IRQ fires (you want it to trigger on both edges) and you report EV_ABS/ABS_X/0. You continue moving to the left and IRQ for left gpio fires up and you report EV_ABS/ABS_X/-1. This assumes that you assign EV_ABS/ABS_X and value 1 for right gpio and EV_ABS/ABS_X and value -1 for left gpio. Thanks. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
