Modern embedded Linux boards with touchscreens usually has a DRM/KMS backend. When bringing up such a board, either a drm and panel driver has to be ported for the target architecture or developed. The drm driver is usually shipped in the BSP offering from the SoC vendor.
Most of the touchscreens are either I2C or SPI based. If a specific touchscreen driver is not found in the Linux kernel or the BSP, it has to be developed.
The modetest utility is usually sufficient to test the LCD panel before porting any utility to test the LCD functionality.
The evtest utility can be used to test the touchscreen.
The drm_multitouch utility can be used to test the touchscreen and the LCD with a bit of fun. Each finger touch results in a colored circle on the screen. Four touch points will display four circles of red, green, blue and white color respectively. The circles can be dragged around the screen.
As this was tested on STM32MP157C-EV1 board, the stm module is used for drm. The first event interface is used for the touchscreen. Code modification will be required to suit your target platform.
Plans are there to add interactive functionality.
The code can be found here.