Hi Paul, On Wed, Dec 20, 2023 at 01:38:39AM +0100, Paul Cercueil wrote: > Hi Peter, > > Le mercredi 20 décembre 2023 à 09:51 +1000, Peter Hutterer a écrit : > > On Mon, Dec 18, 2023 at 11:16:53AM -0600, Chris Morgan wrote: > > > From: Chris Morgan <macromorgan@xxxxxxxxxxx> > > > > > > Stop checking if the minimum abs value is greater than the maximum > > > abs > > > value. When the axis is inverted this condition is allowed. Without > > > relaxing this check, it is not possible to use uinput on devices in > > > userspace with an inverted axis, such as the adc-joystick found on > > > many handheld gaming devices. > > > > As mentioned in the other thread [1] a fair bit of userspace relies > > on > > that general assumption so removing it will likely cause all sorts of > > issues. > > There is some userspace that works with it though, so why restrict it > artificially? > > The fact that some other userspace code wouldn't work with it sounds a > bit irrelevant. They just never encountered that min>max usage before. > > And removing this check won't cause all sort of issues, why would it? > It's not like the current software actively probes min>max and crash > badly if it doesn't return -EINVAL... It will cause weird movements because calculations expect min be the minimum, and max the maximum, and not encode left/right or up/down. Putting this into adc joystick binding was a mistake. This is the definition of absinfo: /** * struct input_absinfo - used by EVIOCGABS/EVIOCSABS ioctls * @value: latest reported value for the axis. * @minimum: specifies minimum value for the axis. * @maximum: specifies maximum value for the axis. * @fuzz: specifies fuzz value that is used to filter noise from * the event stream. * @flat: values that are within this value will be discarded by * joydev interface and reported as 0 instead. * @resolution: specifies resolution for the values reported for * the axis. * * Note that input core does not clamp reported values to the * [minimum, maximum] limits, such task is left to userspace. ... */ (We should change wording of the last sentence to "... does not always clamp ..." since when we do inversion/swap we do clamp values.) And note that the userspace that can handle swapped min and max will work fine if the kernel provides normalized data, but other software will/may not work. Thanks. -- Dmitry
