Hi, based on the current T264 BSP/driver exposure, we only see support for TACH0 and TACH1, and there is no official TACH2 definition or driver path at this time.
So adding a custom TEGRA264_RESET_TACH2 definition alone would not be sufficient to get system support, because this also depends on BPMP ABI, driver support, and actual HW resource exposure.
A third PWM output may still be possible, but a third tach input is not something we can recommend based on the current official software support.