The comment in lv_conf_template.h about LV_TICK_CUSTOM_SYS_TIME_EXPR states that this is an “expression evaluating to current system time in ms”.
In Linux though, this does not necessarily mean the current system wide real-time clock, right? It can for example be the monotonic system clock as well? So I could use clock_gettime with the clock ID being CLOCK_MONOTONIC? I prefer to use that one in Linux because it will not be affected by the user setting the current time and date, while the CLOCK_REALTIME clock will, as will the return value of gettimeofday. But gtkdrv does use gettimeofday (see here), which is why I ask.