You can find the documentation in the i.MX 7Dual Application Processors Reference Manual (available from NXP website).
There are four instances (GPT1-4).
By default the internal clock of 24Mhz is used. There are options to also use external clocks, but they seem to be limited to 1/4 of the peripheral clock (which is 67.5MHz).
The default device tree enables the first GPT1 in the
imx7s.dtsi device tree. Linux does initialize the timer during startup:
clocksource mxc_timer1: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 637086815595 ns
However, the timer is not actually used, Linux uses the ARM architected timer, as noted by a later boot log entry:
Switched to clocksource arch_sys_counter
So you can safely disable the use of the GPT1 timer in Linux by adding
status = "disabled"; in the
gpt1 node. Or just use any of the three other timers.