Hi On Tue, Sep 2, 2014 at 4:40 PM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > On 09/02/2014 02:55 PM, David Herrmann wrote: >> Hi >> >> On Tue, Sep 2, 2014 at 2:43 PM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: >>> Hi, >>> >>> It is useful for userspace to know that they're not dealing with a regular >>> mouse but rather with a pointing stick (e.g. a trackpoint) so that userspace >>> can e.g. automatically enable middle button scrollwheel emulation. >>> >>> It is impossible to tell the difference from the evdev info without resorting >>> to putting a list of device / driver names in userspace, this is undesirable. >> >> ..so it is better to put that table into the kernel? > > No not a table, at the kernel level we actually have different drivers > for pointer sticks and for other mouse (and mouse like devices), so this is > a simple matter of adding a single line of code to all of 4 drivers. > > We could have a table in userspace matching the driver/model strings used > by those 4 drivers, but what if a 5th pops up ? Ok, for now it's pretty easy as all "pointing stick" drivers are already separate in the kernel. But imagine a new generation of "pointing stick" devices is an HID device handled by hid-input.c. What do you do? To set the INPUT_PROPERTY bit, you need to add a driver for this vid/did combination. Seems overkill, so we'd probably not set this property bit for this device and let user-space deal with it. Now we end up with two places to store such information. We already fix scancode/keycode mappings via hwdb as it would be excessive to write kernel drivers for all devices just to fix those. Imo, device properties are very similar to this. We have to draw a line between properties the kernel should detect and expose, and properties we detect in user-space. We already gave up defining ABS_ axes for everything (I mean, we report all kinds of data via ABS_X, ranging from trackpad, to pressure and accelerometer data). User-space needs to detect what devices it deals with, to know what the different axes event-bits mean. Yeah, the POINTING_STICK property turns out to be trivial, so please go ahead. I just want to remind you, that we need a user-space database, anyway. And hwdb entries can be added via simple distro updates (even users can regenerate it themselves). Kernel driver changes are way more heavy.. and slow. Thanks David -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
