On Linux 5.19.10, on my laptop (Dell Inspiron 15R SE 7520) with an Elan v3 touchpad, the reported size of my touchpad (1470 by 700) is half that of the actual touch range (2940 by 1400), and the upper half of my touchpad reports negative values. As a result, with the Synaptics or libinput X11 driver set to edge scrolling mode, the entire right half of my touchpad has x-values past evdev's reported maximum size, and acts as a giant scrollbar! The problem is that elantech_setup_ps2() -> elantech_set_absolute_mode() sets up absolute mode and doubles the hardware resolution (doubling the hardware's maximum reported x/y coordinates and its response to ETP_FW_ID_QUERY), *after* elantech_query_info() fetches the touchpad coordinate system size using ETP_FW_ID_QUERY, which gets cached and reported to userspace through ioctl(fd, EVIOCGABS(ABS_X/Y), ...). So the touchpad size reported to userspace (and used to subtract vertical coordinates from) is half the maximum position of actual touches. This patch series splits out a function elantech_query_range_v3() which fetches *only* ETP_FW_ID_QUERY (touchpad size), and calls it a second time if elantech_set_absolute_mode() enables double-size mode. This means the first call is redundant and wasted if a second call occurs, but this minimizes the need to restructure the driver. A possible alternative approach is to restructure the driver and set resolution before querying touchpad size. I did not attempt this myself, and don't know how the Windows Dell Touchpad ELAN driver handles double-resolution. See https://lore.kernel.org/linux-input/20221008093437.72d0f6b0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ for discussion. Changes in v2: - Fix commit summaries - Add "Fixes:" tag holding commit that introduced bug Link: https://lore.kernel.org/linux-input/CAL57YxZNutUVxBtvbVWKMw-V2kqeVB5kTQ5BFdJmN=mdPq8Q8Q@xxxxxxxxxxxxxx/ Link v1: https://lore.kernel.org/linux-input/20220929082119.22112-1-nyanpasu256@xxxxxxxxx/ Eirin Nya (3): Input: elantech - Remove redundant field elantech_data::y_max Input: elantech - Remove redundant field elantech_data::width Input: elantech - Fix incorrectly halved touchpad range on ELAN v3 touchpads drivers/input/mouse/elantech.c | 51 +++++++++++++++++++++++----------- drivers/input/mouse/elantech.h | 2 -- 2 files changed, 35 insertions(+), 18 deletions(-) base-commit: d4a596eddb90114f5f5f32a440057a175517b090 -- 2.38.0
