hello kko-smol,
you might check pps-gpio driver which uses GPIO pin as PPS source.
$L4T_Sources/r32.4.2/Linux_for_Tegra/source/public/kernel/nvidia/drivers/nvpps/nvpps_main.c
there’s nodes to read timestamp from user-space, and use kernel function to fetch timestamp.
please also check similar discussion thread for reference, Topic 107409.
thanks